Operating Systems

An operating system is a collection of integrated computer programs that provide recurring services to other programs or to the user of a computer. These services consist of disk and file management, memory management, and device management. In other words, it manages CPU operations, input/output activities, storage resources, diverse support services, and controls various devices.
Operating system is the most important program for computer system. Without an operating system, every computer program would have to contain instructions telling the hardware each step the hardware should take to do its job, such as storing a file on a disk. Because the operating system contains these instructions, any program can call on the operating system when a service is needed.

Need to Study Operating System?

There are many different computer systems and several available operating systems. Thus, users must know what each operating system can do and cannot do to meet their necessity. Today, many operating systems are used for general use or sometimes for specific use. Then, which one is best for a specific purpose? The reason that users need to study operating system is here.
The predominant microcomputer operating system for IBM and IBM-compatibles so far was DOS (Disk Operating System). It has different versions including MS-DOS, PC-DOS and others. DOS is very popular and wide spread, but it has some limitations. Users need to learn DOS although it may fade out in a few years and has some weakness, because it will be used for the next several years. The other popular operating system was the Apple Macintosh operating system.
As more powerful microcomputers become commonplace, more advanced operating systems are needed. Microcomputer users are beginning to demand more powerful operating system that can run powerful microcomputers more efficiently. Today's very powerful microcomputers are demanding more complex and refined operating system that can do multifunctions. They also ask an easier user interface than old operating systems did. Now, there are more than six popular operating systems, leading to the lack of a standard. The other reason that operating system should be learned is here.

How the Operating System Uses Memory

Here explains in case of DOS. When a personal computer is turned on, it searches specific locations on the disk drives for operating system files. If the PC finds the files, it loads the first of them into memory. A set of operating system files then takes over, loading the rest of the main files into memory in a specific order. Because the operating system is in a sense, loading itself or lifting itself by its own bootstraps, this operation is called the boot-up.
At the lowest part of memory, the operating system loads a table of interrupt vectors. When the operating system receives special codes called interrupts, it uses the table to detect where in memory it can find matching instructions. DOS also uses a small area just above the interruption table to hold the BIOS data called 'flags' that record the state of various system conditions. The same area also acts as a buffer to store keystrokes that come in faster than the system can process them.
A large expanse of memory just above the BIOS flags and keyboard buffer is used for device drivers, utility programs, and application programs. When DOS reads the CONFIG.SYS and AUTOEXEC.BAT files, it looks for command lines to load drivers or memory-resident programs. Memory- resident programs are those that continue to be active even when application programs are running. When it finds such a command line, DOS normally puts the driver or program at the start of this large memory area. Device drivers usually remain loaded until the PC is turned off. Memory- resident programs can be unloaded if no other programs are loaded after them.

Operating System Functions

An operating system executes many functions to operate computer system efficiently. Among them, four essential functions are the followings.

• Resource Management: An operating system manages a collection of computer hardware resources by using a variety of programs. It manages computer system resources, including its CPU, primary memory, virtual memory, secondary storage devices, input/output peripherals, and other devices.

• Task Management: The function of the operating system that controls the running of many tasks. It manages one program or many programs within a computer system simultaneously. That is, this function of operating system manages the completion of users' tasks. A task management program in an operating system provides each task and interrupts the CPU operations to manage tasks efficiently. Task management may involve a multitasking capability.

• File management: This is a function that manages data files. An operating system contains file management programs that provide the ability to create, delete, enter, change, ask, and access of files of data. They also produce reports on a file.

• User Interface: It is a function of an operating system that allows users to interact with a computer. A user interface program may include a combination of menus, screen design, keyboard commands. A well-designed user interface is essential for an operating system to be popular. Because of the function, users can load programs, access files, and accomplish other tasks.

Virtual Memory

This is a technique for an operating system to manage memory. An operating system simulates significantly larger memory capability than the real memory capacity of its actual primary storage unit. It allows computers to process larger programs than the physical memory circuit would allow.

Multitasking

This refers the capability of operating systems that runs several computing tasks in one computer at the same time. This is controlled by the task management program in an operating system. It's also called multiprogramming and multithreading.