System Boot

• 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

- 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

• 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

• 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

• 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

• 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

• 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.