• Operating system software
• Utility programs
• Library programs
• Translator software (Compiler,
assembler, interpreter).
 System
software (or systems software) is
computer software designed to operate and
control the computer hardware and to
provide a platform for running application
software.[
 The
operating system (prominent examples
being z/OS, Microsoft Windows, Mac OS X
and Linux), allows the parts of a computer to
work together by performing tasks like
transferring data between memory and disks
or rendering output onto a display device. It
also provides a platform to run high-level
system software and application software.
An Operating System is special software that enables
users to communicate with the computer system.
Tasks of an operating system are:
 1. controlling the operation of the input, output and
backing storage devices
 2. supervising the loading, running and storage of
application programs
 3. dealing with errors that occur in applications
programs
 4. maintaining security of the whole computer system
 5. maintaining a computer log, which contains details
of computer usage
 6. allowing communication between user and the
computer system (user interface )
There are two main types of user interface:
 1.
Command line interface (CLI)
 2. Graphical User Interface (GUI) e.g.
WINDOWS (WIMP – Windows Icons Menus
Pointing device)
 Utility
software helps to analyze, configure,
optimize and maintain the computer.
Utility software categories
 Anti-virus utilities scan for computer viruses.
 Archive utilities output a stream or a single file when
provided with a directory or a set of files. Archive
utilities, unlike archive suites, usually do not include
compression or encryption capabilities. Some archive
utilities may even have a separate un-archive utility
for the reverse operation.
 Backup utilities can make a copy of all information
stored on a disk, and restore either the entire disk
(e.g. in an event of disk failure) or selected files
(e.g. in an event of accidental deletion).
 Cryptographic utilities encrypt and decrypt streams
and files.
 Data compression utilities output a shorter stream or
a smaller file when provided with a stream or file.
Utility software categories
 Data synchronization utilities establish consistency among data from a
source to a target data storage and vice versa. There are several
branches of this type of utility:


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File synchronization utilities maintain consistency between two sources. They
may be used to create redundancy or backup copies but are also used to help
users carry their digital music, photos and video in their mobile devices.
Revision control utilities are intended to deal with situations where more than
one user attempts to simultaneously modify the same file.
Disk checkers can scan operating hard drive.
Disk cleaners can find files that are unnecessary to computer operation,
or take up considerable amounts of space. Disk cleaner helps the user to
decide what to delete when their hard disk is full.
Disk compression utilities can transparently compress/uncompress the
contents of a disk, increasing the capacity of the disk.
Disk defragmenters can detect computer files whose contents are
broken across several locations on the hard disk, and move the fragments
to one location to increase efficiency.
Utility software categories
 Disk partitions can divide an individual drive into multiple
logical drives, each with its own file system which can be
mounted by the operating system and treated as an
individual drive.
 Disk space analyzers for the visualization of disk space
usage by getting the size for each folder (including sub
folders) & files in folder or drive. showing the distribution
of the used space.
 Disk storage utilities
 File managers provide a convenient method of performing
routine data management tasks, such as deleting,
renaming, cataloging, uncataloging, moving, copying,
merging, generating and modifying data sets.
 Hex editors directly modify the text or data of a file.
These files could be data or an actual program.
Utility software categories
 Memory testers check for memory failures.
 Network utilities analyze the computer's network
connectivity, configure network settings, check data
transfer or log events.
 Registry cleaners clean and optimize the Windows registry
by removing old registry keys that are no longer in use.
 Screensavers were desired to prevent phosphor burn-in on
CRT and plasma computer monitors by blanking the screen
or filling it with moving images or patterns when the
computer is not in use. Contemporary screensavers are
used primarily for entertainment or security.
 System monitors for monitoring resources and
performance in a computer system.
 System profilers provide detailed information about the
software installed and hardware attached to the computer.
Library Programs
 In
computer science, a library is a collection
of nonvolatile resources used by programs on
a computer, often to develop software.
These may include configuration data,
documentation, help data, message
templates, pre-written code and subroutines,
classes, values or type specifications.
Library Programs
Most compiled languages have a standard
library although programmers can also
create their own custom libraries. Most
modern software systems provide libraries
that implement the majority of system
services
Library Programs
Most compiled languages have a standard
library although programmers can also create
their own custom libraries. Most modern
software systems provide libraries that
implement the majority of system services
Translator software (Compiler, assembler, interpreter).

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A compiler is a computer program (or set of programs) that transforms
source code written in a programming language (the source language)
into another computer language (the target language, often having a
binary form known as object code). The most common reason for wanting
to transform source code is to create an executable program.
The name "compiler" is primarily used for programs that translate source
code from a high-level programming language to a lower level language
(e.g., assembly language or machine code). If the compiled program can
run on a computer whose CPU or operating system is different from the
one on which the compiler runs, the compiler is known as a crosscompiler. A program that translates from a low level language to a higher
level one is a decompiler. A program that translates between high-level
languages is usually called a language translator, source to source
translator, or language converter. A language rewriter is usually a
program that translates the form of expressions without a change of
language.
A compiler is likely to perform many or all of the following operations:
lexical analysis, preprocessing, parsing, semantic analysis (Syntaxdirected translation), code generation, and code optimization.
An assembly language is a low-level programming language for
a computer, microcontroller, or other programmable device, in
which each statement corresponds to a single machine code
instruction. Each assembly language is specific to a particular
computer architecture, in contrast to most high-level
programming languages, which are generally portable across
multiple systems.
Assembly language is converted into executable machine code
by a utility program referred to as an assembler; the conversion
process is referred to as assembly, or assembling the code.
Assembly language uses a mnemonic to represent each low-level
machine operation or opcode. Some opcodes require one or
more operands as part of the instruction, and most assemblers
can take labels and symbols as operands to represent addresses
and constants, instead of hard coding them into the program.
Macro assemblers include a macroinstruction facility so that
assembly language text can be pre-assigned to a name, and that
name can be used to insert the text into other code. Many
assemblers offer additional mechanisms to facilitate program
development, to control the assembly process, and to aid
debugging.
Assembly Language
Example
Interpreter
A program that executes instructions written in a high-level language. There
are two ways to run programs written in a high-level language. The most
common is to compile the program; the other method is to pass the program
through an interpreter.
An interpreter translates high-level instructions into an intermediate form,
which it then executes. In contrast, a compiler translates high-level
instructions directly into machine language. Compiled programs generally run
faster than interpreted programs. The advantage of an interpreter, however, is
that it does not need to go through the compilation stage during which
machine instructions are generated. This process can be time-consuming if the
program is long. The interpreter, on the other hand, can immediately execute
high-level programs. For this reason, interpreters are sometimes used during
the development of a program, when a programmer wants to add small
sections at a time and test them quickly. In addition, interpreters are often
used in education because they allow students to program interactively.
Both interpreters and compilers are available for most high-level languages.
However, BASIC and LISP are especially designed to be executed by an
interpreter. In addition, page description languages, such as PostScript, use an
interpreter. Every PostScript printer, for example, has a built-in interpreter
that executes PostScript instructions.
A compiler translates code from a source
language (e.g. C, C++, Java) to a target
language, which can then be executed by a
(virtual or physical) machine.
An interpreter reads code in an interpreted
language (e.g. PHP, Perl, JavaScript) and
directly executes the contained
instructions.
Compiler characteristics:
•spends a lot of time analyzing and processing
the program
•the resulting executable is some form of
machine- specific binary code
•the computer hardware interprets (executes)
the resulting code
•program execution is fast
Interpreter characteristics:
•relatively little time is spent analyzing and
processing the program
•the resulting code is some sort of intermediate
code
•the resulting code is interpreted by another
program
•program execution is relatively slow