Overview of Unix

Last revision August 2, 2004

The hardware of the computer is made up of four basic parts, the Central Processing Unit (CPU), the memory, secondary storage (disks) and input/output (I/O) devices (terminals, printers, tapes).

These can do nothing without some software or instructions that can be executed by the CPU and tell it how to access other devices and process information received from them. The "operating system" is the basic software that is always accessible to the CPU (either always in memory or in a known location that can be loaded into memory as needed) that tells it how to access and control the resources of the computer.

Functions of the operating system:

• Manages the physical resources of the computer - knows how to get data from the disk or talk to a terminal.
• Arbitrates between processes and users - decides which process (program) gets the CPU or the use of peripherals, for how long, in what order.
• Creates an environment to support user programs: provides a set of basic utilities so that programs can run without needing to know the detailed characteristics of the particular hardware. For example, the operating system provides routines to open a file and read it without having to know the specific geometry of the disk.

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