Technology - Software Systems
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16. Software Systems The information used with computers is known assoftware and includes programs and data.Programs are sets of instructions telling the computer what operations have to be carried out and in what order they should be done. Specialised programs, which enable the computer to be used for particular purposes, are calledapplications programs. A collection of these programs kept in backing store, form what is known as aprogram library. There are two different types of applications programs; namely custom programs and applications packages. Custom programs are designed to suit a particular situation and are usually written by the user himself.Applications packages, however, are more general and are purchased complete with extensive documentation explaining how to use them for particular purposes. Common applications packages includepayroll programs for calculating employees´ wages,database programs for information retrieval,word processor programs for text manipulation andspreadsheet programs for financial planning. Integrated packages have a number of programs combined in one package so that the same data can be shared by them all. Applications programs are usually stored on disc and loaded into the main memory when required. However, they can also be put onto ROM chips to make them immediately available to the user. The programs, which control the basic functions of a computer system, are known as systems programs. They include the operating system, utility (or service) programs, language translators and database management systems. Theoperating system is the most important type of systems software. It consists of a group of programs designed to manage and co-ordinate all the hardware and software of a computer system as efficiently as possible and to provide communications between the computer and the user. It is a very complex piece of software which performs many different functions such as controlling the operation of the disc drives, displaying prompts and cursors, keeping the system running if an error occurs in a program, checking the input of identification numbers and passwords and keeping a log of terminals used in a multi-user system. The operating system must be compatible with the central processor and is usually supplied by the computer manufacturer. If it is stored on ROM chips, in comes into operation as soon as the computer is switched on. Often, however, it is stored on a disc and must be loaded into the main memory before any other operations can be carried out. Utility programs are small systems programs, which perform one simple task. Some utilities perform common tasks known as housekeeping routines. These include copying files from tape to disc, sorting data into alphabetical or numerical order, merging or combining two or more files to make one larger file, cataloguing a disc by displaying the names of the stored files on a VDU screen and performing screen dumps i.e. copying VDU screen displays to a printer. An important utility is theeditor. It allows the user to make changes to programs and data. This would include adding new information, deleting unwanted information and correcting existing information. Language translators form a third type of systems program. Their function is to translate programs written in various computer languages into machine code. They also perform functions such as giving error messages if syntax errors occur in a program and displaying listings of programs on a VDU screen when requested. Language translators include assemblers, compilers and interpreters. Adatabase management system (DBMS) is a set of systems programs, which allow the data from a database to be used by a number of different applications programs. It includes facilities for ensuring the independence, integrity and security of data.