CSE 3-2 : OS Assignment

What are the Functions of an Operating System?

An operating system (OS) is an interface between hardware and user which is responsible for the management and coordination of activities and the sharing of the resources of a computer, that acts as a host for computing applications run on the machine. As a host, one of the purposes of an operating system is to handle the resource allocation and access protection of the hardware. This relieves the application programmers from having to manage these details.

The different functions of an OS are:

1.Memory Management :

When an operating system manages the computer's memory, there are two broad tasks to be accomplished
:

1. Each process must have enough memory in which to execute, and it can neither run into the memory space of another process nor be run into by another process.
2. The different types of memory in the system must be used properly so that each process can run most effectively.

The first task requires the operating system to set up memory boundaries for types of software and for individual applications. When applications begin to be loaded into memory, they are loaded in block sizes determined by the operating system. If the block size is 2 kilobytes, then every process that's loaded will be given a chunk of memory that's a multiple of 2 kilobytes in size. Applications will be loaded in these fixed block sizes, with the blocks starting and ending on boundaries established by words of 4 or 8 bytes. These blocks and boundaries help to ensure that applications won't be loaded on top of one another's space by a poorly calculated bit or two. With that ensured, the larger question is what to do when the 500-kilobyte application space is filled.
A processor can only access memory one location at a time, so the vast majority of RAM is unused at any moment. Since disk space is cheap compared to RAM, then moving information in RAM to hard disk can greatly expand RAM space at no cost. This technique is called virtual memory management
The operating system must balance the needs of the various processes with the availability of the different types of memory, moving data in blocks (called pages) between available memory as the schedule of processes dictates.

2 Process Management :

The heart of managing the processor comes down to two related issues:

• Ensuring that each process and application receives enough of the processor's time to function properly
• Using as many processor cycles as possible for real work

The basic unit of software that the operating system deals with in scheduling the work done by the processor is either a process or a thread, depending on the operating system.
It's tempting to think of a process as an application, but that gives an incomplete picture of how processes relate to the operating system and hardware. The application you see (word processor, spreadsheet or game) is, indeed, a process, but that application may cause several other processes to begin, for tasks like communications with other devices or other computers. There are also numerous processes that run without giving you direct evidence that they ever exist. For example, Windows XP and UNIX can have dozens of background processes running to handle the network, memory management, disk management, virus checks and so on.
A process, then, is software that performs some action and can be controlled -- by a user, by other applications or by the operating system.
The operating system allows the application to begin running, suspending the execution only long enough to deal with interrupts and user input.Interrupts are special signals sent by hardware or software to the CPU. It's as if some part of the computer suddenly raised its hand to ask for the CPU's attention in a lively meeting.
Here’s how a process management is done

• A process occupies a certain amount of RAM. It also makes use of registers, stacks and queues within the CPU and operating-system memory space.
• When two processes are multi-tasking, the operating system allots a certain number of CPU execution cycles to one program.
• After that number of cycles, the operating system makes copies of all the registers, stacks and queues used by the processes, and notes the point at which the process paused in its execution.
• It then loads all the registers, stacks and queues used by the second process and allows it a certain number of CPU cycles.
• When those are complete, it makes copies of all the registers, stacks and queues used by the second program, and loads the first program.

3.File Management:

A file is a collected of related information defined by its creator. Computer can store files on the disk (secondary storage), which provide long term storage. Some examples of storage media are magnetic tape, magnetic disk and optical disk. Each of these media has its own properties like speed, capacity, data transfer rate and access methods.
A file systems normally organized into directories to ease their use. These directories may contain files and other directions.
The five main major activities of an operating system in regard to file management are

1. The creation and deletion of files.
2. The creation and deletion of directions.
3. The support of primitives for manipulating files and directions.
4. The mapping of files onto secondary storage.
5. The back up of files on stable storage media.

4.I/O Organisation:

The I/O system consists of:

• A buffer caching system
• A general device-driver interface
• Drivers for specific hardware devices

5.Security:

The operating system must be capable of distinguishing between requests which should be allowed to be processed, and others which should not be processed. While some systems may simply distinguish between "privileged" and "non-privileged", systems commonly have a form of requester identity, such as a user name. To establish identity there may be a process of authentication. Often a username must be quoted, and each username may have a password. Other methods of authentication, such as magnetic cards or biometric data, might be used instead. In some cases, especially connections from the network, resources may be accessed with no authentication at all (such as reading files over a network share). Also covered by the concept of requester identity is authorization; the particular services and resources accessible by the requester once logged into a system are tied to either the requester's user account or to the variously configured groups of users to which the requester belongs.