IT-213

rem

2009-11-22T18:08:00.000-08:00

import java.io.*;
public class LabExer3 {

public static void main (String[]args)

{

BufferedReader dataIn= new BufferedReader ( new InputStreamReader( System.in));

String name = " ";
System.out.print(" Enter word1: ");

try
{
name=dataIn.readLine();
}catch(IOException e)

{
System.out.println("Error");

}

String name1 = " ";
System.out.print(" Enter word2: ");

try
{
name1=dataIn.readLine();
}catch(IOException e)

{
System.out.print("Error");

}

String name2 = " ";
System.out.print(" Enter word3: ");

try
{
name2=dataIn.readLine();
}catch(IOException e)

{
System.out.print("Error");

}

String name3 = " ";
System.out.print(" Enter word4: ");

try
{
name3=dataIn.readLine();
}catch(IOException e)

{
System.out.println("Error");

}

System.out.println(" " +" "+ name + " "+ name1 +" "+ name2 + " "+ name3 +"!");

}

}

Installation process of Red Hat LINUX

2009-09-21T22:39:00.000-07:00

1.4 LINUX

1) Red Hat Linux Boot screen:

After configuring the system for booting from a CD, the Red Hat Linux Boot screen appears.

At this point, press Enter for the graphical Setup.

2) Welcome to Red Hat:

The "Welcome to Red Hat" screen appears with the option of Hiding the help pane (left side) or viewing the Release Notes.

Select Next when ready.

3) Language Selection:

The Language Selection screen
displays all of the languages available to install Red Hat with.

I chose English here, then Next.

4) Keyboard Configuration:

Keyboard Configuration is next.

Highlight the best match for your particular system. Usually, the default works best.

Select Next when complete.

5) Mouse Configuration:

Mouse Configuration is next.

Again, highlight the best match for your particular system.

Select Next when finished.

6) Installation type:

Selection of a standard installation type is now available.

The options include Personal Desktop, Workstation, Server, or Custom.

For this particular guide, I selected Personal Desktop and then Next.

7) Partitioning your system:

You are now faced with the option of automatically partitioning your system with the default values or selecting a more expert approach of choosing exactly what values each partition will be.

I chose Automatic, then selected Next.

8) Warning dialog box:

If this is a new hard drive or a hard drive that no partitions currently exist, a warning dialog box will appear.

Select Yes to continue.

9) Automatic Partitioning:

Here are the options of deleting all Linux partitions, deleting all partitions, or keep the disk structure as it already is.

If this is a new drive, any options work just fine, but, if you already have partitions defined, as in a Multi-Boot environment, be careful as to which selection and drive volume you choose.

Also, check the Review and modify box at the bottom to retain control over what happens to the hard drive and view the recommended configuration.

10) New hard drive structure:

If you checked the Review and modify box, the new hard drive structure is displayed.

This fits my purposes, so I chose Next to continue.

11) Boot loader options:

Boot Loader options are displayed.

If this is the only OS to be installed, I recommend to install a boot loader, such as Grub (the default).

If this is part of a Multi-Boot System, I recommend to not install a boot loader and use a boot floppy, created later on in the install process, instead.

Important: If you chose to NOT install a boot loader and NOT make a boot floppy, your Red Hat installation will NOT work.

12) Install a boot loader:

Please view my Multi-Boot Guide for more information about Boot Floppies.

13) Network setup:

Network setup options are next.

Enter in the required information for your particular setup, here.

I chose the default, DHCP setup, then selected Next.

14) Firewall setup:

Firewall setup is very important!

If this system will be connected directly to the internet, choose High to start out with.

If this system is already behind a hardware firewall or router, choose Medium as a good starting point.

15) Language Selection:

Additional Language options are also available.

Since I understand no other language besides English, the default was fine.

16) Time Zone Selection:

Configure your Time Zone with this display.

Being on the West Coast, Pacific Time was selected here.

Choose what is right for your location and then select Next to continue.

17) Create a root or administrator password:

Another important part of the installation process is to create a root or administrator password and a "normal" user account for everyday tasks.

DO NOT leave your root password as blank or easily guessable.

18) Add users:

After acceptance of your root password, select the Add button to create an additional account for everyday tasks. Do not worry. If at anytime you need to use the root account to change system settings, you can. You will be prompted for the password even if you are logged in as a regular user.

After creating a new account and selecting a "good" password, select the OK button.

19) Add as many users as you wish:

Your display could look something like this.

Add as many users as you wish, then select Next to continue.

20) Default package configuration:

Here, you have the option of accepting the default package configuration, or selecting exactly what applications and services you desire.

If you wish, you can skip this step and select Next as the default option and your system will be configured accordingly.

However, if you desire to add or subtract particular applications, choose the Customize packages to be installed button and select Next.

21) Selecting exactly what packages:

Here you will have the option of selecting exactly what packages and applications you wish to install.

Detailed descriptions about each are also available, after selecting the check box on the left of the category, by selecting the details button.

Upon completing your options, select Next to continue.

22) Installation will now start:

Installation will now start after selecting the Next button.

23) Formatting of the hard drive:

Formatting of the hard drive or partitions will begin.

Depending on the size of the hard drive, this may take much time.

24) Transfer of the install image:

Transfer of the install image to the hard drive now takes place.

Again, if you selected many packages, this could take some time.

25) Installation of all selected packages:

Installation of all selected packages and applications are now underway.

Depending on what was selected and system configuration, this could take 15 minutes to over an hour.

26) Insert the next CD soon:

Do not go far, though, as you may be required to insert the next CD soon.

27) Boot floppy creation:

If this is the only OS to be installed, I recommend to install a boot loader previously, such as Grub (the default). This does NOT mean that you should forget about creating a boot floppy, also.

If this is part of a Multi-Boot System, I recommend a boot floppy, created here, and not to use a boot loader.

Important: If you chose to NOT install a boot loader and NOT make a boot floppy, your Red Hat installation will NOT work.

Please view my Multi-Boot Guide for more information about boot floppies.

28) Graphics card setup:

Select your graphics card setup and memory configuration here.

Chose Next after highlighting your selection.

29) Monitor Setup:

Enter the proper values or highlight the model of your display here.

After selecting the configuration for your system, chose Next.

30) Desktop resolution:

Choose your desktop resolution and bit-depth.

Capabilities beyond your card should not be displayed.

31) Install complete:

Installation is completed and the system will reboot after selecting Next.

32) Grub boot loader:

Upon reboot, the Grub (if selected previously in the install process) is displayed with the option of booting your Linux installation.

If you opted for a boot floppy, ensure that your system is configured to boot from "A:" first, then your hard drive, otherwise, your system may skip to your previous OS by default.

33) Boot Red Hat:

Keep in mind, while the OS is loading, Linux is famous for allowing the USER to choose exactly what, how and why everything happens.

This is not Windows.

You will see all kinds of information about the internal workings of your system.

Do not be alarmed. You will come to enjoy that information in due time. :)

34) Logon:

If you opted for a graphical install screen, the user name prompt is displayed.

35) Gnome Desktop:

The Red Hat 8.0 default desktop is now displayed. If you selected KDE and not Gnome, your view will be slightly different.

Remember, anything that you wish to do, you can, including messing with system files.

When in doubt, think twice. :)

36) BlackViper.com in Mozilla:

I had to fire up Mozilla 1.0.1 to ensure my internet connectivity functioned, and it worked great!

Thank you for viewing my install guide and I hope it has helped you gain an insight to what may be required before taking the Red Hat plunge.

Installation process of Windows VISTA

2009-09-21T22:38:00.000-07:00

1.2 VISTA

1) Shall we begin?

After configuring the system for booting from a CD/DVD, the Windows Setup screen appears.

At this point, Setup is loading the driver files it needs to continue with installation.

2) Progress Bar:

The next screen is a more graphical progress bar indicating Windows Vista is still working in the background.

3) Option Selections:

The first options you will come across are selections for Language, Time and currency format, and Keyboard layout.

Make your selections by using the pull down menus and press the Next button.

4) Install Now:

Here we have the option of repairing a previous installation or "Install Now."

Highlight the "Install Now" button to continue to the next screen.

5) Please Wait:

Windows Vista is working in the background. This may take several minutes depending on the system.

7) License Agreement:

Here we see the License Agreement you must accept before continuing.

After reading the agreement, check the box next to "I accept the license terms".

8) Option Selections:

Here we would be able to choose an "Upgrade" install (if running setup from a previous version of Windows, such as XP) or a "Custom" (clean) install.

Select the whole box containing "Custom (advanced)" to continue to the next screen.

9) Hard Drives:

This is where you can select which hard drive/partition to install Vista on. Since this system only has one hard drive, only one place Vista can go. Advanced options are shown in the next screen shot.

This is also where you would install drivers for your RAID/ACPI controller by using the "Load Driver" option. After the installation of the RAID/ACPI drivers, your hard drives should appear as shown on the right.

If no additional drivers are needed, select the Next button.

Image 2.5: (40KB .gif)

10) Advanced Options:

The advanced options allow creation of multiple partitions and the option of formatting existing partitions.

After finishing your particular partition configuration that you desire, select the Next button.

6) Product Key:

This screen is where you enter your product key or "CD Key" as it is sometimes called.

An option also exists to automatically activate Vista upon first coming online. I uncheck this box to ensure everything is running smoothly before activating and having issues later on. 30 days is the standard amount of time before activation is required, though some products (such as MSDN subscriptions) have 60 days or more.

After entering your product key, press the Next button.

11) Installing...:

Here is where Vista installs major components of the OS. This process can take 10 to 60 minutes depending on the system.

12) Reboot:

Here we see the system needing to reboot to continue installation tasks.
You can hit the Restart Now button or just allow the reboot to happen automatically after several seconds.

13) First Time:

Here we see a "..." progress as Vista tries to start for the first time. This process may take several minutes before going to the next screen.

14) Completing Installation:

Vista continues to install at this screen. Depending on system, another reboot or two may happen before the next screen is displayed.

15) Account Creation:

Here is where we create the first user account for the system and select an icon to be displayed on the login screen. Ensure you password your account.
After finishing entering your information and icon selection, select the Next button.

16) PC Name:

Here is where we can name the system for networking purposes. By default, it uses the account name entered in the previous step and adds "-PC" to it. We can also select a background for the desktop.
After making your selection, select the Next button.

17) Updates:

Here we can configure Windows Update with several options. I suggest "Use recommended options" or the top option for most PC users.

18) Time Settings:

Here is where you can set the time and daylight savings time options.
After configuring your time zone, clock settings and date, select the Next button.

19) Network Configuration:

Vista now asks our network configuration by asking "Home, Work or Public Place."
Descriptions are expanded on screen so I will no go into them here.
Make your selection to continue to the next screen.

20) Thanks!:

On this screen, we are thanked by Bill G. for installing Windows Vista.
After you are done being thanked, select the Next button.

21) PC Performance:

Vista now checks the system performance to automaticlly configure a few options. This may take several minutes while the system does this and it will only do it this one time.

22) Login:

We are finally greeted with the login screen, however, there is still more configuration to come.
Enter in your password that you used previously during the install process and hit ENTER or the little blue arrow to login.

23) Desktop Setup:

Your account profile starts being created here starting with your personal desktop configuration. More happens on the next screen. This process will also take several minutes, but only happen once.

24) Account Profile:

Vista now sets up profile configurations for Internet Explorer, Windows Media Player as well as a few more Windows applications. This could take several more minutes but we are almost there!

25) Welcome Screen:

Vista is installed!

Installation Process of Windows XP

2009-09-21T22:37:00.000-07:00

1.3 2000

1) Windows Setup Screen:

Shall we begin?

After configuring the system for booting from a CD, the Windows Setup screen appears.

At this point, Setup is loading the driver files it needs to continue with installation.

2) Welcome to Setup:

The Welcome to Setup screen appears with the option of Continuing Setup, Repair a previous installation, or Quitting.

Press ENTER to Continue Setup, R to Repair, or F3 to Quit and reboot the system.

3) Windows 2000 Licensing Agreement:

The Windows 2000 Licensing Agreement screen, otherwise known as EULA,
displays the legal in's and out's of this particular software package.

You may press F8 to signify that you agree with the terms, hit ESC if you do not agree and PAGE UP or PAGE DOWN to scroll
through each screen. Note: If you do not agree to the terms, setup will quit and reboot the system.

4) Hard drive partition information:

Hard drive partition information is now displayed. This varies with each systems hardware
configuration.

This example already has a partition defined. I will choose not to use this and create a new one by pressing D.
You may skip this and the next few steps if you do not have any partitions defined.

At this point, the options include pressing ENTER to Install on the selected partition, D to Delete the selected partition,
or F3 to Quit and reboot the system.

5) Warning screen:

After pressing D to delete the selected partition, a warning screen appears explaining
the pitfalls of deleting it. This particular screen only appears when the partition selected to be deleted is formatted as
a bootable system partition. Other partitions will display the next screen.

I want this to happen, so I press ENTER to continue.

The options include pressing ENTER to continue, or ESC to Cancel.

6) Confirmation screen:

A confirmation screen that displays the logical drive, what file system the partition is
currently using, the size in MB and controller information.

Options include L to Delete the partition and ESC to Cancel the action.

7) No partitions have been previously defined:

If no partitions have been previously defined, this screen will be displayed. You may section
your hard drive in as many partitions as you wish by selecting C to Create a Partition and then entering in a value less then
the total available. Here, I will Create a Partition in the highlighted, unused portion.

Select the partition you wish to install to using the UP ARROW and DOWN ARROW keys.

Press ENTER to use the highlighted partition and Install, C to Create a Partition, or F3 to Quit and reboot the system.

8) Enter in the partition size:

Enter in the partition size in MB within the displayed minimum and maximum. I chose the default
or maximum available here.

You may choose ENTER to Create the new partition or ESC to Cancel the action.

9) Continue to create partitions:

Continue to create partitions until all space is used or the configuration meets your requirements.
Note: a small portion will be unavailable to partition. This is normal. In this example, it is 4 MB.

I chose drive C: to install the Operating system.

You may choose ENTER to Install to the selected partition, D to Delete the highlighted Partition, or F3 to Quit and reboot
the system.

10) Format the partition:

Since this OS supports NTFS, format the partition with it. If you do not, many folder and
file security features will be unavailable. Note: If you are dual booting your system, a previous OS will not be able to read
the local information. This is a fact with Windows 9x and Me. If you have a requirement to view this partition from another
OS installed on the system, do not format it as NTFS. Also, the boot partition must be formatted with FAT32 if you wish to
dual boot. I have found no problems accessing a NTFS partition mapped as a network drive from an older OS.

Select what format you wish to use by pressing the UP ARROW and DOWN ARROW keys.

Press ENTER to confirm your selection and Continue or ESC to Cancel.

11) Setup formats the partition:

Watch the progress bar as Setup formats the partition, or get up and get a soda. It may take
awhile.

12) Creating File List:

Setup is now figuring out what files to copy over to the hard drive.

13) Setup copies various files:

After the partition is finished formatting, Setup copies various files to support booting
from the hard drive and continue on.

14) Creating various information files:

Setup then creates various information files required to continue on with setup.

15) Press `ENTER` to Restart

The first reboot and the end of the blue background has arrived. If you are impatient, press
ENTER to Restart before the 15 seconds expire.

ENTER to Restart the Computer is the only option available.

16) Windows 2000 boot screen:

The new Windows 2000 boot screen is displayed.

17) Windows 2000:

Sit back. It may be awhile.

18) Setup Wizard:

The Setup Wizard will be displayed. SelectNext to continue on.

19) Installing Devices:

Windows 2000 will begin installing devices, such as "mouse and keyboard," even though you have already been using them. :)

20) Region and Input Languages: (Image 2.5)

A little while later, you will be prompted with options of configuring your Region and Input
Languages. The default was fine for me, so I selected Next.

Options include Customize buttons plus the standard Back and Next.

21) Enter in your name:

Enter in your name and optional Organization information, then select the Next button.

22) 25 digit Product Key:

Thought you could get away from it? Think again.

Enter your unique 25 digit Product Key that came with your CD, then select the Next button.

23) Enter a Computer name and an Administrator Password: (Image 2.8)

The "suggested" name for the computer is always really whacked out. Choose one
that meets your needs.

Enter an Administrator Password now. It is very important that you keep this information safe and remember what it is!

"01Pa$$word" is not a good choice. Think of something secure and never lose or forget it.

24) Date, Time and Time Zone:

Configure the proper information for the Date, Time and Time Zone here.

25) Network Setup:

Networking information is now setting up.

26) Network Settings Dialog: (Image 3.1)

The Network Settings Dialog is next. Under usual circumstances, the Typical settings are fine, but I never choose them so I can poke around under the hood. I selected Custom here.

Choose your method and select the Next button.

27) Custom settings:

TCP/IP Properties contains the standard options. Adjust them for your particular needs as
required. For now, I kept the default settings. Basically, it is using DHCP to configure TCP/IP.

Select the Advanced button to further configure your TCP/IP options.

In the custom settings, many options are abound. I cannot go into all of them here, so I will leave everything as default.

28) Workgroup or Computer Domain?

Workgroup or Computer Domain, that is the question. I am not going to set up this system
to connect to a domain controller, so I will place it as a member of a workgroup.

Please, change "WORKGROUP" to something else. I hate defaults. :)

Select the Next button after making your choice and entering your configuration.

29) Copying files:

Installation of all files and components may take awhile. Sit back and watch the pretty bar wander across the screen. :)

30) Final Tasks:

After the files finish the transfer, setup performs final tasks. including setting up the start menu and cleaning up temporary directories.

31) Setup Finished:

The system will reboot after selecting the Finish button on this dialog.

32) Windows 2000 is starting up: (Image 4.1)

The moment we have all been waiting for, Windows 2000 Professional is starting up "for
the first time." Remember that quoted statement with Windows 95 setup?

33) Network Wizard:

Windows 2000 Network ID Wizard is displayed with the option of canceling or selecting Next.

I chose Next here.

34) Click Back:

At this point, an initial option was not offered.

Click the Back button to see it.

35) Choose your option:

Here, I choose to select the second option of The computer is part of a home network and not part of a business network.

Does it make any difference? Not sure, but it makes me feel better.

After choosing your option, select Next to continue.

36) Auto Login:

Windows 2000 offers the ability for you, right now, to create a user account, password it, and "always login" as this person.

This is what I "usually" do as I have no worries about anyone in the house cracking the system, but if your circumstances warrant it, I would not have auto login enabled. However, you should still create a "normal" user account and not always use the Administrator account for daily activities.

NEVER leave an account unpassworded.

37) Windows 2000 Desktop:

Since I chose to auto login, I did not get the pop up dialog asking for password.

The desktop is now displayed!

I hope this gave you some insight as how "easy" it really is to install Windows 2000.

Graphs

2009-08-27T03:11:00.000-07:00

Unsafe State in Resource-
allocation Graph

-

Resource-Allocation Graph For
Deadlock Avoidance

-

Resource Allocation Grap with a
cycle but no deadlock

Example of research Allocation
graph w/ a deadlock

Example of research Allocation
graph

Resource Allocation Graph

2009-08-27T02:01:00.000-07:00

Resource allocation graph & Wait-for graph

A set of vertices V and a set of edges E.

* V is partitioned into two types:

>FP = {P1, P2, …, Pn}, the set consisting of all the processes in the system.

>FR = {R1, R2, …, Rm}, the set consisting of all resource types in the system.

* request edge – directed edge P1 ---> Rj
* assignment edge – directed edge Rj ---> Pi

How could you know if theres a deadlock based w/ the Resouce Allocation table?

*If graph contains no cycles Þ no deadlock.

*If graph contains a cycle Þ
-if only one instance per resource type, then deadlock.
-if several instances per resource type, possibility of deadlock.

Methods For Handling Deadlocks

2009-08-20T04:00:00.000-07:00

*Deadlock Prevention

- Disallow one of the four necessary conditions

for dealock.

*Deadlock Avoidance

-Do not grant a resource request if this allocation

have potential to lead to a deadlock

*Deadlock Detection

- Always grant resource request when possible.

Periodically check for deadlock. If deadlock exists,

recover from it.

*Ignore the problem

- Makes sense if the likelihood is very low.

Deadlock Recovery

2009-08-20T03:54:00.000-07:00

*Abort all deadlock processes and release resource - too drastic - will lead to loss of work

*Abort one process at a time - releasing resources until no deadlock
How do we determine which process to abort first ? - priority ordering, process which has done least work

*Selectively restart processes from a previous checkpoint i.e. before it claimed any resources difficult to achieve - sometimes impossible

*Successively withdraw resources from a process and give to another process until deadlock is broken. How to choose which processes and which resources ?

1)Complex decisions due to the large number of processes present within a system

2)fficult to automate

3) Operator to resolve conflicts - BUT this requires the operator to have skill and understanding of what processes are actually doing

Deadlock Characterization

2009-08-20T03:50:00.000-07:00

A deadlock can occur if the following four conditions hold
simultaneously:

1. Mutual exclusion: at least one resource must be held in a
nonsharable mode.

2. Hold and wait: a process must be holding at least one
resource and waiting to acquire additional resources held by
other processes.

3. No preemption: resources can’t be preempted.

4. Circular wait: there exists a set {P0, P1, …, Pn} of waiting
processes such that P0
is waiting for a resource that is held by

P1, P1 is waiting for a resource that is held by P2, …, Pn–1 is
waiting for a resource that is held by Pn, and Pn is waiting for a
resource that is held by P0.

Deadlock Detection

2009-08-20T03:48:00.000-07:00

• Allow system to enter deadlock state

• Detection algorithm

•Recovery scheme

Deadlock Prevention

2009-08-20T03:42:00.000-07:00

• At least 1 necessary condition does not hold– Mutual Exclusion: not required for sharable resources; must hold for non-sharable resources.– Hold-and-Wait: can not request new when
holding resources.
• Protocol 1: request all resources before it begins execution
• Protocol 2: request resources only when the process has none.
• Low resource utilization; starvation possible.– No Preemption: preempt resources from processes
• Protocol 1: If a request can not be satisfied then preempt all resources held and block
• Protocol 2: Preempt only if resources are needed by another running process
• Requires resource state to be easily restored– Circular Wait: Block any request that results in a cycle.
• Impose a total ordering of all resource types, and require that each process requests resources in an increasing order

REAL-TIME SCHEDULING

2009-08-17T22:43:00.000-07:00

Hard real-time systems – required to complete a critical task within a guaranteed amount of time
Soft real-time computing – requires that critical processes receive priority over less fortunate ones

Thread Scheduling

2009-08-13T04:17:00.000-07:00

Across platforms, thread scheduling1 tends to be based on at least the following criteria:

*a priority, or in fact usually multiple "priority" settings that we'll discuss below;

*a quantum, or number of allocated timeslices of CPU, which essentially determines the amount of CPU time a thread is allotted before it is forced to yield the CPU to another thread of the same or lower priority (the system will keep track of the remaining quantum at any given time, plus its default quantum, which could depend on thread type and/or system configuration);

*a state, notably "runnable" vs "waiting";

*metrics about the behaviour of threads, such as recent CPU usage or the time since it last ran (i.e. had a share of CPU), or the fact that it has "just received an event it was waiting for".

Most systems use what we might dub priority-based round-robin scheduling to some extent. The general principles are:

*a thread of higher priority (which is a function of base and local priorities) will preempt a thread of lower priority;

*otherwise, threads of equal priority will essentially take turns at getting an allocated slice or quantum of CPU;

*there are a few extra "tweaks" to make things work.

Multiprocessor Scheduling

2009-08-13T04:08:00.000-07:00

In computer science, multiprocessor scheduling is an NP-Complete optimization problem. The problem statement is: "Given a set J of jobs where job ji has length li and a number of processors mi, what is the minimum possible time required to schedule all jobs in J on m processors such that none overlap?" The applications of this problem are numerous, but are, as suggested by the name of the problem, most strongly associated with the scheduling of computational tasks in a multiprocessor environment.

Scheduling Algorithms

2009-08-10T22:42:00.000-07:00

1.First-come, first-served (FCFS) scheduling
2.Shortest-job first (SJF) scheduling
3.Priority scheduling
4.Round-robin scheduling
5.Multilevel queue scheduling
6.Multilevel feedback queue scheduling

- First-come, First-served (FCFS) scheduling is the simplest scheduling algorithm, but it can cause short processes to wait for very long processes.

- Shortest-job-first (SJF) scheduling is provably optimal, providing the shortest average waiting time. Implementing SJF scheduling is difficult because predicting the length of the next CPU burst is difficult. The SJF algorithm is a special case of the general priority-scheduling algorithm, which simply allocates the CPU to the highest-priority process. Both priority and SJF scheduling may suffer from starvation. Aging is a technique to prevent starvation.

- Round-robin (RR) scheduling is more appropriate for a time-shared (interactive) system. RR scheduling allocates the CPU to the first process in the ready queue for q time units, where q is the time quantum. After q time units, if the process has not relinquished the CPU, it is preempted and the process is put at the tail of the ready queue. The major problem is the selection of the time quantum. If the quantum is too large, RR scheduling degenerates to FCFS scheduling; if the quantum is too small, scheduling overhead in the form of context-switch time becomes excessive.

The FCFS algorithm is nonpreemptive, the RR algorithm is preemptive. The SJF and priority algorithms may be either preemptive or nonpreemptive.
Multilevel queue algorithms allow different algorithms to be used for various classes of processes. The most common is a foreground interactive queue which uses RR scheduling, and a background batch queue, which uses FCFS scheduling. Multilevel feedback queues allow processes to move from one queue to another.
Because such a wide variety of scheduling algorithms are available, we need methods to select among them. Analytic methods use mathematical analysis to determine the performance of an algorithm. Simulation methods determine performance by imitating the scheduling algorithm on a “representative” sample of processes, and computing the resulting performance.
Operating Systems supporting threads at the kernel level must schedule threads - not processes
- for execution. This is the case with Solaris 2 and Windows 2000 where both systems schedule threads using preemptive priority based on scheduling algorithm including support for real-time threads.

The Linux process scheduler also uses a priority-based algorithm with real-time supports as well. The scheduling algorithms for these three operating systems typically favor interactive over batch and CPU-bound processes.systems typically favor interactive over batch and CPU-bound processes.

Multithreading Models

2009-07-30T03:45:00.001-07:00

Many-to-one

In this model, the library maps all threads to a single lightweight process Advantages: totally portable easy to do with few systems dependencies Disadvantages: cannot take advantage of parallelism may have to block for synchronous I/O there is a clever technique for avoiding it Mainly used in language systems, portable libraries

One-to-one

In this model, the library maps each thread to a different lightweight process Advantages: can exploit parallelism, blocking system calls Disadvantages: thread creation involves LWP creation each thread takes up kernel resources limiting the number of total threads Used in LinuxThreads and other systems where LWP creation is not too expensive.

Many-to-many

n this model, the library has two kinds of threads: bound and unbound bound threads are mapped each to a single lightweight process unbound threads may be mapped to the same LWP Probably the best of both worlds Used in the Solaris implementation of Pthreads (and several other Unix implementations) .

Thead Library

2009-07-30T03:42:00.000-07:00

The Thread Library (TL) is a software feature that enables the computer to run programs written to use POSIX Threads fairly efficiently and conscies.

Kernel mode

2009-07-30T03:38:00.000-07:00

kernel directly supports multiple threads of control in a process

Benefits:scheduling/synchronization coordination, less overheadthan process, suitable for parallel application

Drawbacks:more expensive than user-level threads, generalityleads to greater overhead

User Thread

2009-07-30T03:33:00.000-07:00

user libraries implementation

Benefits:no kernel modifications, flexible and low cost

Drawbacks:thread may block entire process, no parallelism

Benifits of Multi-threaded Programming

2009-07-30T03:32:00.000-07:00

Responsiveness

Resource Sharing

Economy

Utilization of MP Architectures

Theard

2009-07-30T03:11:00.000-07:00

Single-threaded process

- Single threaded process have one path of execution, and multi-threaded programs have two or more paths of execution. Single threaded programs can perform only one task at a time, and have to finish each task in sequence before they can start another. For most programs, one thread of execution is all you need, but sometimes it makes sense to use multiple threads in a program to accomplish multiple simultaneous tasks.

Multi-threaded process

Each process can include many threads.

All threads of a process share:

–memory (program code and global data)

–open file/socket descriptors

–signal handlers and signal dispositions

–working environment (current directory, user ID, etc.)

Producer

2009-07-30T02:27:00.000-07:00

*Producer :
»get a message block from mayproduce

»put data item in block

»send message to mayconsume

*consumer :

»get a message from mayconsume

»consume data in block

»return empty message block to mayproduce mailbox

Buffering

2009-07-30T02:26:00.000-07:00

•Buffering - the number of messages that can reside in a link temporarily

–Zero capacity - queue length 0

»sender must wait until receiver ready to take the message

–Bounded capacity - finite length queue
»messages can be queued as long as queue not full

»otherwise sender will have to wait

–Unbounded capacity

»any number of messages can be queued - in virtual space?

»sender never delayed

Interprocess Communication

2009-07-30T02:10:00.000-07:00

Direct Communication

–each process wanting to communicate must explicitly name the recipient or sender of the communication

–send and receive primitives defined:
send ( P, message ) : send a message to process P
receive ( Q, message ) : receive a message from process Q

–a link established automatically between every pair of processes that want to communicate
»processes only need to know each other’s identity

–link is associated with exactly two processes

–link is usually bidirectional but can be unidirectional

– Process A Process Bwhile (TRUE) { while (TRUE) { produce an item receive ( A, item ) send ( B, item ) consume item} }

Indirect Communication

•messages sent to and received from mailboxes (or ports)

–mailboxes can be viewed as objects into which messages placed by processes and from which messages can be removed by other processes

–each mailbox has a unique ID

–two processes can communicate only if they have a shared mailbox

send ( A, message ) : send a message to mailbox Areceive ( A, message ) :

receive a message from mailbox A

Synchronization

- Message passing may be either blocking or non-blocking.

• Blocking is considered synchronous

• Non-blocking is considered asynchronous

- Send and receive primitives may be either blocking or non-blocking.

Inter-process communication

2009-07-16T03:26:00.000-07:00

Inter-process communication (IPC) is a set of techniques for the exchange of data among multiple threads in one or more processes. Processes may be running on one or more computers connected by a network. IPC techniques are divided into methods for message passing, synchronization, shared memory, and remote procedure calls (RPC).

The method of IPC used may vary based on the bandwidth and latency of communication between the threads, and the type of data being communicated.

There are several reasons for providing an environment that allows process cooperation:
Information sharing Computation speedup Modularity Convenience IPC may also be referred to as inter-thread communication and inter-application communication.
IPC, on par with the address space concept, is the foundation for address space independence/isolation.[1]

Cooperating processes

2009-07-16T03:23:00.000-07:00

Once we have multiple processes or threads, it islikely that two or more of them will want tocommunicate with each other

• Process cooperation (i.e., interprocesscommunication) deals with three main issues

– Passing information between processes/threads

– Making sure that processes/threads do not interfere witheach other

– Ensuring proper sequencing of dependent operations

• These issues apply to both processes and theads– Initially we concentrate on shared memory mechanismswe have multilple

Operating in Process

2009-07-16T02:55:00.000-07:00

Process Creation

Parent process creates children processes, which, in turn create other processes, forming a tree
of processes.Resource sharing:

>Parent and children share all resources.

>Children share subset of parent’s resources.

>Parent and child share no resources.

Execution:

>Parent and children execute concurrently.

>Parent waits until children terminate.

Process termination

>Process executes last statement and asks the operating system to delete it (exit).

>Output data from child to parent (via wait).

>Process’ resources are deallocated by operating system.>Parent may terminate execution of children processes (abort).

>Child has exceeded allocated resources.

>Task assigned to child is no longer required.

>Parent is exiting.

>Operating system does not allow child to continue if its parent terminates.

>Cascading termination.

Process Scheduling

2009-07-16T02:51:00.000-07:00

Scheduling Queues

>Job queue – set of all processes in the system.

>Ready queue – set of all processes residing in main memory, ready and waiting to execute

device

>Device queues – set of processes waiting for an I/O device.

>Processes migrate between the various queues.

Schedules

>Long-term scheduler (or job scheduler) – selects which processes should be brought into the ready queue.

>Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU.

Control Switch

>When CPU switches to another process, the system must save the state of the old process and load the saved state for the new process.

>Context-switch time is overhead; the system does no useful work while switching.

>Time dependent on hardware support.

Process

2009-07-16T01:43:00.000-07:00

Process State

In a multitasking computer system, processes may occupy a variety of states. These distinct states may not actually be recognized as such by the operating system kernel, however they are a useful abstraction for the understanding of processes.

Process Control Block

-Information associated with each process.

>Process ID

>Process state

>Program countern CPU registers

>CPU scheduling information

>Memory-management information

>Accounting information

>I/O status information

Threads

In computer science, a thread of execution results from a fork of a computer program into two or more concurrently running tasks. The implementation of threads and processes differs from one operating system to another, but in most cases, a thread is contained inside a process. Multiple threads can exist within the same process and share resources such as memory, while different processes do not share these resources.

On a single processor, multithreading generally occurs by time-division multiplexing (as in multitasking): the processor switches between different threads. This context switching generally happens frequently enough that the user perceives the threads or tasks as running at the same time. On a multiprocessor or multi-core system, the threads or tasks will generally run at the same time, with each processor or core running a particular thread or task. Support for threads in programming languages varies: a number of languages simply do not support having more than one execution context inside the same program executing at the same time.

Examples of such languages include Python, and OCaml, because the parallel support of their runtime support is limited by the use of a central lock, called "Global Interpreter Lock" in Python, "master lock" in Ocaml. Other languages may be limited because they use threads that are user threads, which are not visible to the kernel, and thus cannot be scheduled to run concurrently. On the other hand, kernel threads, which are visible to the kernel, can run concurrently.

System Boot

2009-07-07T03:52:00.000-07:00

Operating system must be made available to hardware so hardware can start it

-Small piece of code – bootstrap loader, locates the kernel, loads it into memory, and starts it

-Sometimes two-step process where boot block at fixed location loads bootstrap loader

-When power initialized on system, execution starts at a fixed memory location

Firmware used to hold initial boot code

System Generation

2009-07-07T03:50:00.000-07:00

- Operating systems are designed to run on any of a class of machines; the system must be configured for each specific computer site

- SYSGEN program obtains information concerning the specific configuration of the hardware system- Booting

– starting a computer by loading the kernel- Bootstrap program

– code stored in ROM that is able to locate the kernel, load it into memory, and start its execution

Virtual Machine

2009-07-07T03:49:00.000-07:00

A virtual machine was originally defined by Popek and Goldberg as "an efficient, isolated duplicate of a real machine". Current use includes virtual machines which have no direct correspondence to any real hardware.[1]
Virtual machines are separated into two major categories, based on their use and degree of correspondence to any real machine. A system virtual machine provides a complete system platform which supports the execution of a complete operating system (OS). In contrast, a process virtual machine is designed to run a single program, which means that it supports a single process. An essential characteristic of a virtual machine is that the software running inside is limited to the resources and abstractions provided by the virtual machine -- it cannot break out of its virtual world.
Example: A program written in Java receives services from the Java Runtime Environment (JRE) software by issuing commands to, and receiving the expected results from, the Java software. By providing these services to the program, the Java software is acting as a "virtual machine", taking the place of the operating system or hardware for which the program would ordinarily be tailored.

System virtual machines
See also: Virtualization and Comparison of virtual machinesSystem virtual machines (sometimes called hardware virtual machines) allow the sharing of the underlying physical machine resources between different virtual machines, each running its own operating system. The software layer providing the virtualization is called a virtual machine monitor or hypervisor. A hypervisor can run on bare hardware (Type 1 or native VM) or on top of an operating system (Type 2 or hosted VM).
The main advantages of system VMs are:
multiple OS environments can co-exist on the same computer, in strong isolation from each other the virtual machine can provide an instruction set architecture (ISA) that is somewhat different from that of the real machine application provisioning, maintenance, high availability and disaster recovery[2] Multiple VMs each running their own operating system (called guest operating system) are frequently used in server consolidation, where different services that used to run on individual machines in order to avoid interference are instead run in separate VMs on the same physical machine. This use is frequently called quality-of-service isolation (QoS isolation).
The desire to run multiple operating systems was the original motivation for virtual machines, as it allowed time-sharing a single computer between several single-tasking OSes. This technique requires a process to share the CPU resources between guest operating systems and memory virtualization to share the memory on the host.
The guest OSes do not have to be all the same, making it possible to run different OSes on the same computer (e.g., Microsoft Windows and Linux, or older versions of an OS in order to support software that has not yet been ported to the latest version). The use of virtual machines to support different guest OSes is becoming popular in embedded systems; a typical use is to support a real-time operating system at the same time as a high-level OS such as Linux or Windows.

System Structure

2009-07-02T04:08:00.000-07:00

Simple Structure

-->View the OS as a series of levels

-->Each level performs a related subset of functions

-->Each level relies on the next lower level to perform more primitive functions

-->This decomposes a problem into a number of more manageable subproblems

Layred Approach

The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.
With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers.
A process is a program in execution. A process needs certain resources: CPU time, memory (address space), files, and I/O devices, to accomplish its task.

System Calls

2009-07-02T04:00:00.000-07:00

Process control

Process control is a statistics and engineering discipline that deals with architectures, mechanisms, and algorithms for controlling the output of a specific process. See also control theory.

For example, heating up the temperature in a room is a process that has the specific, desired outcome to reach and maintain a defined temperature (e.g. 20°C), kept constant over time. Here, the temperature is the controlled variable. At the same time, it is the input variable since it is measured by a thermometer and used to decide whether to heat or not to heat. The desired temperature (20°C) is the setpoint. The state of the heater (e.g. the setting of the valve allowing hot water to flow through it) is called the manipulated variable since it is subject to control actions.

File Management

Also referred to as simply a file system or filesystem. The system that an operating system or program uses to organize and keep track of files. For example, a hierarchical file system is one that uses directories to organize files into a tree structure. Although the operating system provides its own file management system, you can buy separate file management systems. These systems interact smoothly with the operating system but provide more features, such as improved backup procedures and stricter file protection.

Device management

Device Management is a set of technologies, protocols and standards used to allow the remote management of mobile devices, often involving updates of firmware over the air (FOTA). The network operator, handset OEM or in some cases even the end-user (usually via a web portal) can use Device Management, also known as Mobile Device Management, or MDM, to update the handset firmware/OS, install applications and fix bugs, all over the air. Thus, large numbers of devices can be managed with single commands and the end-user is freed from the requirement to take the phone to a shop or service center to refresh or update.

Information Maintainance

Information management (IM) is the collection and management of information from one or more sources and the distribution of that information to one or more audiences. This sometimes involves those who have a stake in, or a right to that information. Management means the organization of and control over the structure, processing and delivery of information.

Throughout the 1970s this was largely limited to files, file maintenance, and the life cycle management of paper-based files, other media and records. With the proliferation of information technology starting in the 1970s, the job of information management took on a new light, and also began to include the field of Data maintenance. No longer was information management a simple job that could be performed by almost anyone. An understanding of the technology involved, and the theory behind it became necessary. As information storage shifted to electronic means, this became more and more difficult. By the late 1990s when information was regularly disseminated across computer networks and by other electronic means, network managers, in a sense, became information managers. Those individuals found themselves tasked with increasingly complex tasks, hardware and software. With the latest tools available, information management has become a powerful resource and a large expense for many organizations.

Operating System Service

2009-07-02T03:38:00.000-07:00

Operating systems are responsible for providing essential services within a computer system:
* Initial loading of programs and transfer of programs between secondary storage and main memory
*Supervision of the input/output devices
*File management
*Protection facilities

System Components

2009-07-02T03:14:00.000-07:00

Operating systems Process Management

The operating system is responsible for the following activities in connection with process management.

-->Process creation and deletion.

-->Process suspension and resumption.

-->Provision of mechanisms for:

-->Process synchronization

->Process communication

Main memory management
Memory management is the act of managing computer memory. In its simpler forms, this involves providing ways to allocate portions of memory to programs at their request, and freeing it for reuse when no longer needed. The management of main memory is critical to the computer system.
Virtual memory systems separate the memory addresses used by a process from actual physical addresses, allowing separation of processes and increasing the effectively available amount of RAM using disk swapping. The quality of the virtual memory manager can have a big impact on overall system performance.
Garbage collection is the automated allocation, and deallocation of computer memory resources for a program. This is generally implemented at the programming language level and is in opposition to manual memory management, the explicit allocation and deallocation of computer memory resources.

File management Also referred to as simply a file system or filesystem. The system that an operating system or program uses to organize and keep track of files. For example, a hierarchical file system is one that uses directories to organize files into a tree structure. Although the operating system provides its own file management system, you can buy separate file management systems. These systems interact smoothly with the operating system but provide more features, such as improved backup procedures and stricter file protection.

I/O System management

The I/O system consists of:

-->A buffer-caching system

-->A general device-driver interface

-->Drivers for specific hardware devices

Secondary Storage System
Secondary storage management is a classical feature of database management systems. It is usually supported through a set of mechanisms. These include index management, data clustering, data buffering, access path selection and query optimization.
None of these is visible to the user: they are simply performance features. However, they are so critical in terms of performance that their absence will keep the system from performing some tasks (simply because they take too much time). The important point is that they be invisible. The application programmer should not have to write code to maintain indices, to allocate disk storage, or to move data between disk and main memory. Thus, there should be a clear independence between the logical and the physical level of the system.
Protection System

Protection refers to a mechanism for controlling access by programs, processes, or users to both system and user resources.
The protection mechanism must:

-->Distinguish between authorized and unauthorized usage.

-->Specify the controls to be imposed.

-->Provide a means of enforcement.

Command-Interpreter System
A command-line interpreter (also command line shell, command language interpreter) is a computer program that reads lines of text entered by a user and interprets them in the context of a given operating system or programming language.

Hardware Protection

2009-06-25T03:28:00.001-07:00

•Dual -Mode Operation-sharing system resources requires operating system to ensure that an incorrect program connot cause other programs to execute incorrectly.

-provides hardware support to differenciate atleast up to two modes of operation.

1. User mode-execution done on behalf of a user.

2. Monitor mode-execution done on behalf of a operating system.

•I/O Protection-All i/o instructions are priveleged instructions.

-must ensure that a user program could never gain control

of the computer in monitor mode.

•Memory Protection-Memory protection is a way to control memory access rights on a computer, and is a part of nearly every modern operating system. The main purpose of memory protection is to prevent a process from accessing memory that has not been allocated to it. This prevents a bug within a process from affecting other processes, or the operating system itself. Memory protection also makes a Rootkit more difficult to implement. Memory protection is a behavior that is distinct from ASLR and the NX bit.
•CPU protection-to prevent a user programs gets stuck in infinite loop and never returning back to the os

Storage Hierarchy

2009-06-25T02:51:00.000-07:00

* Caching-In computer science, a cache (pronounced /kæʃ/) is a collection of data duplicating original values stored elsewhere or computed earlier, where the original data is expensive to fetch (owing to longer access time) or to compute, compared to the cost of reading the cache. In other words, a cache is a temporary storage area where frequently accessed data can be stored for rapid access. Once the data is stored in the cache, it can be used in the future by accessing the cached copy rather than re-fetching or recomputing the original data.
A cache has proven to be extremely effective in many areas of computing because access patterns in typical computer applications have locality of reference. There are several kinds of locality, but this article primarily deals with data that are accessed close together in time (temporal locality). The data might or might not be located physically close to each other (spatial locality).

*Coherency-In computing, cache coherence (also cache coherency) refers to the integrity of data stored in local caches of a shared resource. Cache coherence is a special case of memory coherence.
When clients in a system maintain caches of a common memory resource, problems may arise with inconsistent data. This is particularly true of CPUs in a multiprocessing system. Referring to the "Multiple Caches of Shared Resource" figure, if the top client has a copy of a memory block from a previous read and the bottom client changes that memory block, the top client could be left with an invalid cache of memory without any notification of the change. Cache coherence is intended to manage such conflicts and maintain consistency between cache and memory.

*Consistency- in theory is one that does not contain a contradiction. The lack of contradiction can be defined in either semantic or syntactic terms. The semantic definition states that a theory is consistent if it has a model; this is the sense used in traditional Aristotelian logic, although in contemporary mathematical logic the term satisfiable is used instead. The syntactic definition states that a theory is consistent if there is no formula P such that both P and its negation are provable from the axioms of the theory under its associated deductive system.
If these semantic and syntactic definitions are equivalent for a particular logic, the logic is complete. The completeness of sentential calculus was proved by Paul Bernays in 1918 and Emil Post in 1921, while the completeness of predicate calculus was proved by Kurt Gödel in 1930. Stronger logics, such as second-order logic, are not complete.

Storage Structure

2009-06-25T02:50:00.000-07:00

•Main Memory--Computer data storage, often called storage or memory, refers to computer components, devices, and recording media that retain digital data used for computing for some interval of time. Computer data storage provides one of the core functions of the modern computer, that of information retention. It is one of the fundamental components of all modern computers, and coupled with a central processing unit (CPU, a processor), implements the basic computer model used since the 1940s.In contemporary usage, memory usually refers to a form of semiconductor storage known as random access memory (RAM) and sometimes other forms of fast but temporary storage. Similarly, storage today more commonly refers to mass storage - optical discs, forms of magnetic storage like hard disks, and other types slower than RAM, but of a more permanent nature. Historically, memory and storage were respectively called primary storage and secondary storage.

•Magnetic Disk-Magnetic Disk-Magnetic storage and magnetic recording are terms from engineering referring to the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetization in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads. As of 2009, magnetic storage media, primarily hard disks, are widely used to store computer data as well as audio and video signals. In the field of computing, the term magnetic storage is preferred and in the field of audio and video production, the term magnetic recording is more commonly used. The distinction is less technical and more a matter of preference10.Storage Hierarchy-The hierarchical arrangement of storage in current computer architectures is called the memory hierarchy. It is designed to take advantage of memory locality in computer programs. Each level of the hierarchy has the properties of higher bandwidth, smaller size, and lower latency than lower levels

•Moving Head Disk Mechanism-

•Magnetic Tapes-Magnetic tape is a medium for magnetic recording generally consisting of a thin magnetizable coating on a long and narrow strip of plastic. Nearly all recording tape is of this type, whether used for recording audio or video or for computer data storage. It was originally developed in Germany, based on the concept of magnetic wire recording. Devices that record and playback audio and video using magnetic tape are generally called tape recorders and video tape recorders respectively. A device that stores computer data on magnetic tape can be called a tape drive, a tape unit, or a streamer.

1) Bootstrap program

2009-06-23T04:20:00.000-07:00

In computing, bootstrapping (from an old expression "to pull oneself up by one's bootstraps") is a technique by which a simple computer program activates a more complicated system of programs. In the start up process of a computer system, a small program such as BIOS, initializes and tests that hardware, peripherals and external memory devices are connected, then loads a program from one of them and passes control to it, thus allowing loading of larger programs, such as an operating system.

A different use of the term bootstrapping is to use a compiler to compile itself, by first writing a small part of a compiler of a new programming language in an existing language to compile more programs of the new compiler written in the new language. This solves the "chicken and egg" causality dilemma.

2) Difference of interrupt and trap and there use.

2009-06-23T04:18:00.000-07:00

The difference between interrupt and trap is that in computing and operating systems, a trap is a type of synchronous interrupt typically caused by an exceptional condition (e.g. division by zero or invalid memory access) in a user process. A trap usually results in a switch to kernel mode, wherein the operating system performs some action before returning control to the originating process. In some usages, the term trap refers specifically to an interrupt intended to initiate a context switch to a monitor program or debugger.[1]

In SNMP, a trap is a type of PDU used to report an alert or other asynchronous event about a managed subsystem. While interrupt is an asynchronous signal indicating the need for attention or a synchronous event in software indicating the need for a change in execution. A hardware interrupt causes the processor to save its state of execution via a context switch, and begin execution of an interrupt handler.
Software interrupts are usually implemented as instructions in the instruction set, which cause a context switch to an interrupt handler similar to a hardware interrupt.
Interrupts are a commonly used technique for computer multitasking, especially in real-time computing. Such a system is said to be interrupt-driven.[1]
An act of interrupting is referred to as an interrupt request (IRQ).

3)monitor mode

2009-06-23T04:17:00.001-07:00

Monitor mode, or RFMON (Radio Frequency Monitor) mode, allows a computer with a wireless network interface card (NIC) to monitor all traffic received from the wireless network. Unlike promiscuous mode, which is also used for packet sniffing, monitor mode allows packets to be captured without having to associate with an access point or ad-hoc network first. Monitor mode only applies to wireless networks, while promiscuous mode can be used on both wired and wireless networks. Monitor mode is one of the six modes that 802.11 wireless cards can operate in: Master (acting as an access point), Managed (client, also known as station), Ad-hoc, Mesh, Repeater, and Monitor mode.

4)User mode

2009-06-23T04:08:00.001-07:00

It is a non-privileged mode in which each process (i.e., a running instance of a program) starts out. It is non-privileged in that it is forbidden for processes in this mode to access those portions of memory (i.e., RAM) that have been allocated to the kernel or to other programs. The kernel is not a process, but rather a controller of processes, and it alone has access to all resources on the system.
When a user mode process (i.e., a process currently in user mode) wants to use a service that is provided by the kernel (i.e., access system resources other than the limited memory space that is allocated to the user program), it must switch temporarily into kernel mode, which has root (i.e., administrative) privileges, including root access permissions (i.e., permission to access any memory space or other resources on the system). When the kernel has satisfied the process's request, it restores the process to user mode.
This change in mode is termed a mode switch, which should not be confused with a context switch (i.e., the switching of the CPU from one process to another). The standard procedure to switch from user mode to kernel mode is to call the 0x80 software interrupt.
An interrupt is a signal to the operating system that an event has occurred, and it results in changes in the sequence of instructions that is executed by the CPU. In the case of a hardware interrupt, the signal originates from a hardware device such as a keyboard (e.g., when a user presses a key), mouse or system clock (a circuit that generates pulses at precise intervals that are used to coordinate the computer's activities). A software interrupt is an interrupt that originates in software, usually by a program in user mode.

5)Device status table

2009-06-23T04:07:00.002-07:00

6)Direct memory access

2009-06-23T04:06:00.000-07:00

Direct memory access (DMA) is a feature of modern computers and microprocessors that allows certain hardware subsystems within the computer to access system memory for reading and/or writing independently of the central processing unit. Many hardware systems use DMA including disk drive controllers, graphics cards, network cards and sound cards. DMA is also used for intra-chip data transfer in multi-core processors, especially in multiprocessor system-on-chips, where its processing element is equipped with a local memory (often called scratchpad memory) and DMA is used for transferring data between the local memory and the main memory. Computers that have DMA channels can transfer data to and from devices with much less CPU overhead than computers without a DMA channel. Similarly a processing element inside a multi-core processor can transfer data to and from its local memory without occupying its processor time and allowing computation and data transfer concurrency.

Without DMA, using programmed input/output (PIO) mode for communication with peripheral devices, or load/store instructions in the case of multicore chips, the CPU is typically fully occupied for the entire duration of the read or write operation, and is thus unavailable to perform other work. With DMA, the CPU would initiate the transfer, do other operations while the transfer is in progress, and receive an interrupt from the DMA controller once the operation has been done. This is especially useful in real-time computing applications where not stalling behind concurrent operations is critical. Another and related application area is various forms of stream processing where it is essential to have data processing and transfer in parallel, in order to achieve sufficient throughput.

7)Difference of ram and dram

2009-06-23T04:05:00.001-07:00

Random-access memory (usually known by its acronym, RAM) is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order (i.e., at random). The word random thus refers to the fact that any piece of data can be returned in a constant time, regardless of its physical location and whether or not it is related to the previous piece of data.[1]

By contrast, storage devices such as tapes, magnetic discs and optical discs rely on the physical movement of the recording medium or a reading head. In these devices, the movement takes longer than data transfer, and the retrieval time varies based on the physical location of the next item.

The word RAM is often associated with volatile types of memory (such as DRAM memory modules), where the information is lost after the power is switched off. Many other types of memory are RAM, too, including most types of ROM and flash memory called NOR-Flash.

while the dram is a feature of modern computers and microprocessors that allows certain hardware subsystems within the computer to access system memory for reading and/or writing independently of the central processing unit. Many hardware systems use DMA including disk drive controllers, graphics cards, network cards and sound cards. DMA is also used for intra-chip data transfer in multi-core processors, especially in multiprocessor system-on-chips, where its processing element is equipped with a local memory (often called scratchpad memory) and DMA is used for transferring data between the local memory and the main memory. Computers that have DMA channels can transfer data to and from devices with much less CPU overhead than computers without a DMA channel. Similarly a processing element inside a multi-core processor can transfer data to and from its local memory without occupying its processor time and allowing computation and data transfer concurrency.

Without DMA, using programmed input/output (PIO) mode for communication with peripheral devices, or load/store instructions in the case of multicore chips, the CPU is typically fully occupied for the entire duration of the read or write operation, and is thus unavailable to perform other work. With DMA, the CPU would initiate the transfer, do other operations while the transfer is in progress, and receive an interrupt from the DMA controller once the operation has been done. This is especially useful in real-time computing applications where not stalling behind concurrent operations is critical. Another and related application area is various forms of stream processing where it is essential to have data processing and transfer in parallel, in order to achieve sufficient throughput.

8)Main Memory

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Refers to physical memory that is internal to the computer. The word main is used to distinguish it from external mass storage devices such as disk drives. Another term for main memory is RAM.

9)Magnetic Disk

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Are terms from engineering referring to the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetization in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads. As of 2009, magnetic storage media, primarily hard disks, are widely used to store computer data as well as audio and video signals. In the field of computing, the term magnetic storage is preferred and in the field of audio and video production, the term magnetic recording is more commonly used. The distinction is less technical and more a matter of preference.

10)Storage Hierarchy

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The range of memory and storage devices within the computer system. The following list starts with the slowest devices and ends with the fastest. See storage and memory.

1) What’s the difference of OS in terms of users view and the system view?

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The difference between of OS in terms of the users view and systems view is that in the users view is that how an os makes a computer convenient to use. the Effeciency : An os allows the computer system resource to be used in a effecient manner and lastly abilty to evolve: An OS should be constructed in such a way to permit the effective development,testing,and introduction of new system function without interfering with service.
While the operating system interms of the systems view is that a operating system manages the sharig resources among competing entites, provides a number of common services that make application easier to wrtie and serves as the interface between application and programs

2) Explain the goals of OS.

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The various roles or goals of and operating system generally revolve around the idea of “sharing nicely”.
An Operating system manages resources, and these resources are often shared in one way or another among programs that want to use them

3) What’s the difference bet. batch system ,multiprogrammed systems, and time-sharing systems?

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The difference bet. batch system ,multiprogrammed systems, and time-sharing systems is that batch system is one in which jobs are bundled together with the instructions necessary to allow them to be processed without intervention. Often jobs of a similar nature can be bundled together to further increase economy, then the multiprogrammed systems is a method by which multiple tasks, also known to processes , share common processing resources such as CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for that task while time-sharing is were you have a primary computer or shall we say the sever and there you would connect the other computers and the server will serve as the main PC.

4) Advantages of Parallel system.

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The advantage of having a Parallel system is that the certain PC having this system has a higher performance rate, has a higher response time, efficient to use of a faster interconnection network essential for good performance and can perform tasks that a non-parallel system operating system could not do. It could also use two hardware platforms with different performance characteristics to validate some conclusion or data processed.

5) Differentiate Symmetric multiprocessing and Asymmetric multiprocessing.

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Asymmetric multiprocessing or ASMP is a type of multiprocessing supported in DEC's VMS V.3 as well as a number of older systems including TOPS-10 and OS-360. It varies greatly from the standard processing model that we see in personal computers today. Due to the complexity and unique nature of this architecture, it was not adopted by many vendors or programmers during its brief stint between 1970 - 1980.
Where as a symmetric multiprocessor or SMP treats all of the processing elements in the system identically, an ASMP system assigns certain tasks only to certain processors. In particular, only one processor may be responsible for fielding all of the interrupts in the system or perhaps even performing all of the I/O in the system. This makes the design of the I/O system much simpler, although it tends to limit the ultimate performance of the system. Graphics cards, physics cards and cryptographic accelerators which are subordinate to a CPU in modern computers can be considered a form of asymmetric multiprocessing. SMP is extremely common in the modern computing world, when people refer to "multi core" or "multi processing" they are most commonly referring to SMP.

6) Differentiate client-server system and peer-to-peer system.

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The difference between client-server and peer-to-peer system is that the client to server is a computing system composed of two logical parts: a server, which provides information or services, and a client, which requests them. On a network, for example, users can access server resources from their personal computers using client software while the peer-to-peer system is a networking method of delivering computer network services in which the participants share a portion of their own resources, such as processing power, disk storage, network bandwidth, printing facilities. Such resources are provided directly to other participants without intermediary network hosts or servers

7) Differentiate the design issues of OS between stand alone PC and a workstation connected to a network.

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-The Stand alone PC is just like your own PC, it doesn't connect with the other PC's, while the Workstation connected PC is compose of one or two PC's but attached by two or more monitors.

8) Define the following types of OS: Batch, Time sharing, Real Time, Network, Distributed,Handheld

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a. Batch- are set up so they can be run to completion without human interaction, so all input data is preselected through scripts or command-line parameters. This is in contrast to "online" or interactive programs which prompt the user for such input. A program takes a set of data files as input, process the data, and produces a set of output data files. This operating environment is termed as "batch processing" because the input data are collected into batches on files and are processed in batches by the program. b. Time Sharing- is sharing a computing resource among many users by multitasking. Its introduction in the 1960s, and emergence as the prominent model of computing in the 1970s, represents a major historical shift in the history of computing. By allowing a large number of users to interact simultaneously on a single computer, time-sharing dramatically lowered the cost of providing computing, while at the same time making the computing experience much more interactive c. Real Time-In computer science, real-time computing (RTC) is the study of hardware and software systems that are subject to a "real-time constraint"—i.e., operational deadlines from event to system response. By contrast, a non-real-time system is one for which there is no deadline, even if fast response or high performance is desired or preferred. The needs of real-time software are often addressed in the context of real-time operating systems, and synchronous programming languages, which provide frameworks on which to build real-time application software d. Network- networked systems consist of multiple computers that are networked together, usually with a common operating system and shared resources. Users, however, are aware of the different computers that make up the system. e. Distributed-Distributed computing deals with hardware and software systems containing more than one processing element or storage element, concurrent processes, or multiple programs, running under a loosely or tightly controlled regime. f. Handheld-Handheld is common names for mobile devices such as Hand-held camera, Hand-held computer, Handheld computing ,Handheld (gaming),Handheld electronic game