System software:What is system software?

What is system software?

When we apply a computer to the task of writing a letter or keeping records, we use application software. That applica­tion software resides in the computer's memory alongside a more basic level of software called system software. The application software does not have to tell the computer exactly how to access a disk or keyboard or control the screen display, as the system software looks after this. System software is fundamental to the computer- when you buy the computer, you also buy this software- for without it the computer can't do anything.

System software is made up of the operating system, a number of additional utilities, and, on many computers, software which provides a user-friendly operating environment.

• The operating system controls the disk-drives and other hardware devices and, in the case of networked com­puters, the network operations. It also allows you to carry out computer housekeeping tasks such as loading, copying, and deleting files.

• The operating environment provides an easy-to-use way of carrying out housekeeping tasks as well as providing friendly environment within which computer applica­tions can be run.

• Utilities provide additional facilities and routines.

In this chapter we'll look at each of these three types of systems software. The next chapter introduces application software.

Operating systems

A computer's operating system enables it to carry out its disk filing and other operational tasks. We can put these tasks under five headings:

• Basic input/output operations, such as controlling the screen display. This is governed by the part of the operating system often known as the BIOS (Basic Input/ Output System).

• Disk operations, which are to do with storing programs and data on disk. This is governed by the part of the operating system which on PCs is called DOS (Disk Operating System).

• Network operations, which enable a number of micros to be linked to each other and to share facilities such as hard disks and printers.

• Multi-tasking, which enable the computer to handle several tasks at the same time, such as running a record­ keeping application, a spreadsheet, and a word processing program.

• Multiuser operations, which allow a number of people to use a computer and its software at the same time, by connecting to it other PCs or workstations.

Some operating systems on microcomputers are only able to handle the first two of these groups of tasks. As I've said, computers based on the Intel 80x86 family of microproces­sors (i.e. PCs) use an operating system called DOS, short for 'disk operating system'. In the case of the IBM PC, its full name is PC-DOS, short for 'Personal computer disk operating system'; in the case of the compatible PCs from other manufacturers, its full name is MS-DOS, the MS being short for 'Microsoft', the software house that wrote DOS. In spite of the differences in name, the two products are, for all practical purposes, identical. DOS was developed from the earlier CP/M operating system used on Z80-based microcomputers.

Over the years, DOS has grown steadily more powerful, and has passed through several versions or 'levels'. Each version has added features which support new hardware developments, such as the ability to handle hard disks, 3.5

inch disks, and so on. The current version is level 4. The version designed for the IBM PS/2 microcomputers is called OS/2, and this supports multitasking.

Digital Research Corporation, which is Microsoft's main competitor, sells a competing operating system for PCs called Concurrent DOS. This offers the following features:

• Multitasking with up to four 'windows' visible at any time on the screen, each running a different program.

• Multiuser facilities for up to three users, using PCs or workstations linked to an IBM-AT or compatible.

• Compatibility with DOS, so that programs written for that operating system will run without difficulty.

A more powerful operating system, which runs on larger computers and also on more powerful PCs (i.e. those based on the 80386 chip and above), is Unix. This is designed with multitasking and multiuser applications in mind, and is steadily increasing in popularity as microcomputers become more powerful and more capable of operating in these modes. It is worth noting that the 'Helios' operating system being developed for the new generation of transputer-based computers is based upon Unix.

Other types of computer use different operating systems. For example, the 680x0 based Atari ST uses the TOS operating system.

How the operating system organizes the disk

Storing, organizing, and retrieving files are central tasks for all operating systems. To understand these systems, it is therefore necessary to know something of the principles of disk filing. This is covered in the sections below.

First, note that each file, whether it is a program file supplied by a software house or a data or text file that you have produced, is given a name. That name, together with the location of the file on the disk, is stored in the index, a special area on the disk's surface. When you type the filename, the operating system looks it up in the index, locates the file, and loads it into RAM.