As you
know, system software acts as an interface for the underlying hardware system.
Here we will discuss some important system software in detail.
Operating System
Operating system (OS) is the lifeline of computer. You connect all
the basic devices like CPU, monitor, keyboard and mouse; plug in the power
supply and switch it on thinking you have everything in place. But the computer
will not start or come to life unless it has an operating system installed in
it because OS −
- Keeps all
hardware parts in a state of readiness to follow user instructions
- Co-ordinates
between different devices
- Schedules
multiple tasks as per priority
- Allocates
resource to each task
- Enables
computer to access network
- Enables users
to access and use application software
Besides
initial booting, these are some of the functions of an operating system −
- Managing
computer resources like hardware, software, shared resources, etc.
- Allocating
resources
- Prevent error
during software use
- Control
improper use of computer
One of
the earliest operating systems was MS-DOS, developed by Microsoft for
IBM PC. It was a Command Line Interface (CLI) OS that revolutionized
the PC market. DOS was difficult to use because of its interface. The users
needed to remember instructions to do their tasks. To make computers more
accessible and user-friendly, Microsoft developed Graphical User Interface
(GUI) based OS called Windows, which transformed the way people used
computers.
Assembler
Assembler
is a system software that converts assembly level programs to machine level
code.
These
are the advantages provided by assembly level programming −
- Increases
efficiency of the programmer as remembering mnemonics is easier
- Productivity
increases as number of errors decreases and hence debugging time
- Programmer has
access to hardware resources and hence has flexibility in writing programs
customized to the specific computer
Interpreter
The
major advantage of assembly level language was its ability to optimize memory
usage and hardware utilization. However, with technological advancements
computers had more memory and better hardware components. So ease of writing
programs became more important than optimizing memory and other hardware
resources.
In
addition, a need was felt to take programming out of a handful of trained
scientists and computer programmers, so that computers could be used in more
areas. This led to development of high level languages that were easy to
understand due to resemblance of commands to English language.
The
system software used to translate high level language source code into machine
level language object code line by line is called an interpreter. An
interpreter takes each line of code and converts it into machine code and
stores it into the object file.
The advantage of
using an interpreter is that they are very easy to write and they do not
require a large memory space. However, there is a major disadvantage in using
interpreters, i.e., interpreted programs take a long time in executing. To
overcome this disadvantage, especially for large programs, compilers were
developed.
Compiler
System
software that store the complete program, scan it, translate the complete
program into object code and then creates an executable code is called a
compiler. On the face of it compilers compare unfavorably with interpreters
because they −
- are more
complex than interpreters
- need more
memory space
- take more time
in compiling source code
However,
compiled programs execute very fast on computers. The following image shows the
step-by-step process of how a source code is transformed into an executable
code −
These
are the steps in compiling source code into executable code −
·
Pre-processing − In this stage pre-processor instructions,
typically used by languages like C and C++ are interpreted, i.e. converted to
assembly level language.
·
Lexical
analysis − Here all instructions are
converted to lexical units like constants, variables, arithmetic
symbols, etc.
·
Parsing − Here all instructions are checked to see if
they conform to grammar rules of the language. If there are errors,
compiler will ask you to fix them before you can proceed.
·
Compiling − At this stage the source code is converted
into object code.
·
Linking − If there are any links to external files or
libraries, addresses of their executable will be added to the program. Also, if
the code needs to be rearranged for actual execution, they will be rearranged.
The final output is the executable code that is ready to be executed.
