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Unit 13: Library Software

it is provided an essential software that makes it ready to use. An operating system is software,
which makes the computer ready to use by a process called booting. Notes

Types of Operating Systems
Many operating systems are available for computers which can be divided into the two types : (i)
Single-user operating systems, and (ii) Multi-user operating systems.
(i) Single-user Operating Systems. These operating systems are used for mainly computers having
only one terminal (stand-alone PCs). MS DOS (Microsoft Disk Operating System) and PC DOS
(Personal Computer Disk Operating System) are the two important single-user operating systems.
Both systems are almost identical and are simply called DOS.
(ii) Multi-user Operating Systems. These operating systems are used for those computers (micro to
mainframe) which have many terminals (multi-user systems). The popular operating systems used
for multi-user systems are UNIX, NETWARE, MVS, OS/400, VMS and Linux. OS/2 and Windows
NT are other popular multi-user, multi-tasking operating systems for microcomputers.

13.3 Language Translators

We give instructions to computer using a language. A set of instructions is called a Program and the
language using which we give the instructions is called the Programming Language or Computer
Language or simply Language. There are many types of computer languages such as Machine
Language, High Level Languages, etc. Although we can give instructions to computer using any
language, internally it understands only the machine language. The machine language consists of
two numbers only i.e., 0s and 1s. Regardless of the programming language used (except machine
language), the symbolic instructions have to be translated into a form, that can be executed by
computer. The software, which converts the codes of other languages into machine code, are
collectively called Language Translators.
Language Translators are categorised into the following three types :
(a) Interpreters
(b) Compilers
(c) Assemblers
Interpreters
Instructions of a high-level language are coded in many statements. At the time of their execution,
they are converted statement by statement into machine code, by using system software, called
Interpreters. For example, programs written in BASIC language are executed by using BASICA or
GWBASIC interpreters. Programs written in some fourth generation languages, like dBASE III plus
are also executed using dBASE interpreter. There are certain disadvantages of interpreters. As
instructions are translated and executed simultaneously using interpreters, interpreters are very
slow for executing large programs. Hence, they are not suitable for the most of applications
development.

Compilers
As contrast to interpreters, compilers provide faster execution speed. Compilers do not translate
and execute the instructions at the same time. They translate the entire program (source code) into
machine code (object code). Using linker, the object code is converted into executable code. Compilers
are widely used in translating codes of high level languages (e.g., COBOL, FORTRAN, Pascal, Turbo/
Quick BASIC, Turbo/ Microsoft C etc.) and fourth generation languages (dBASE IV, Foxpro, etc.).
As compared to interpreters or assemblers, compilers are preferred in development of application
software.

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