SYSTEM PROGRAMMING

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SYSTEM PROGRAMMING SYSTEM ADMINISTRATION

• UNIT-1

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What Is System Program

• System Programs were developed to make computers
  better adapted to the needs of their users.
• Some examples of system program are
• Compliers
• Loaders
• Macro processors
• Operating systems

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Brief Introduction

• Complier- They are systems programs that accept
  people-like languages translate them into
  machine language.
• Loaders- They prepare machine language program
  for execution.
• Macro processors- They allow programmers to use
  abbreviations.
• Operating Systems file system-They allow
  flexible storing retrieval of information.

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ASSEMBLERS

• It is difficult for programmers to write or read
  programs in machine language.
• So they began to use a mnemonic (symbol) for each
  machine instruction ,which they would
  subsequently translate into machine language.
• Such a mnemonic language is known as ASSEMBLY
  LANGUAGE.

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ASSEMBLERS cont.

• Assemblers are programs written to automate the
  translation of assembly language in to machine
  language.
• The input to an assembler program is called the
  source program.
• The output is a machine translation (object
  program).

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ASSEMBLERS cont.

• An assembly language is a machine dependent, low
  level programming language which is specific to a
  certain computer system . Three basic features
  which simplify programming
• Mnemonic operation codes
• Symbolic operands
• Data declarations

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Execution of program written in a language L
involves the following steps

1. Translation of the program- by translator
2. Linking of the program with other programs needed
   for its execution-by linker
3. Relocation of the program to execute from the
   specific memory area allocated to it
4. Loading of the program in the memory for the
   purpose of execution-by loader

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Program Execution
Data
Binary Program
Translator
Linker
Loader
Results
Source Program
Binary Programs
Objects Modules
Data flow
Control flow
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LOADERS

• A loader is a program that places programs into
  memory prepares them for execution.
• In a simple loading scheme, the assembler outputs
  the machine language translation of a program on
  a secondary device a loader is placed in core
  (memory).
• Subroutines- It is a body of computer
  instruction designed to be used by others
  routines to accomplish a task.

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LOADERS cont.

• Two types of subroutines are
• Closed subroutines It can be stored outside the
  main routine control transfers to the
  subroutine.
• Open subroutines It is one whose code is
  inserted into main program.

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MACROS

• Macro processing facility which permits the
  programmer to define an abbreviation for a part
  of his program to use the abbreviation in his
  program.
• The macro processor treats the identical parts of
  program defined by the abbreviation as a macro
  definition saves the definition.

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COMPLIERS

• A complier is a program that accepts a program
  written in a high level language produces an
  object program.
• Example of high-level language are
• FORTRAN
• COBOL
• ALCOL
• Interpreter It is a program that appears to
  execute a source program as if it were machine
  language.

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SOFTWARE TOOLS

• Program that help in developing using other
  programs. These programs, called software tools.
• Definition- A software tool is a system program
  which
• Interfaces a program with the entity generating
  its input data.
• Interfaces the results of a program with the
  entity consuming them.

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A Software tool
Originator
Software
Consumer
Raw Program or Data
Transformed Program or Data
A Software tool
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Software Tools For Program Development

1. Program design, coding, documentation
2. Preparation of programs in machine readable form
3. Program translation, linkage loading
4. Program testing debugging
5. Performance tuning
6. Reforming the data and/or results of a program to
   suit other programs.

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1. Program Design Coding

• Two categories of tools used in program design
  coding are
• Program generators- It generates a program which
  performs a set of functions described in its
  specification
• Programming environments-It supports program
  coding by incorporating awareness of the
  programming language syntax semantics in the
  lang. editor

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2. Program Entry Editing

• These are text editors or more sophisticated
  programs with text editors as front ends.
• The editor functions in 2 modes-
• Command mode
• Data mode

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Program Testing Debugging

• Main steps in this are selection of test data for
  the program, analysis of test results to detect
  errors, debugging i.e. localization removal of
  errors.
• Software tools to assist the programmer in these
  steps are-
• Test data generators
• Automated test drivers
• Debug monitors
• Source code control systems

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EDITORS

• Forms of Editors
• Line Editors
• Steam Editors
• Screen Editors
• Word Processors
• Structure Editors

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EDITORS cont

• Line Editors- The scope of edit operations in a
  line editor is limited to a line of text. The
  line is designed positionally,e.g. by specifying
  its serial number in the text, or contextually,
  e.g. by specifying a context which uniquely
  identifies it.

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EDITORS cont

• Stream Editors- A stream editor views the entire
  text as a stream of characters. They typically
  supports characters, line, context oriented
  commands based on the current editing context
  indicated by the position of a text pointer.

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EDITORS cont

• Screen Editors - A line or stream editors does
  not display the text in the manner it would
  appear if printed. A screen editor uses the
  what-you see-is-what-you-get principle in editor
  design. This is very useful while formatting the
  text to produce printed documents.

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EDITORS cont

• Word processors- They are document editors with
  additional features to produce well formatted
  hard copy output. Essentials features are
  commands for moving sections of text from one
  place to another, merging of text, searching
  replacement of words. Many word processor support
  a spell-check option.

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EDITORS cont

• Structures Editors- A structure editor
  incorporates an awareness of the structure of a
  document. This is useful in browsing through a
  document ,e.g. if a programmer wishes to edit a
  specific function in a file.

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DEBUG MONITORS

• It provide the following facilities for dynamic
  debugging
• Setting breakpoints in the program
• Initiating a debug conversation when control
  reaches a breakpoint
• Display values of variables
• Assigning new values to variables
• Testing user defined assertions predicates
  involving program variables.

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DEBUG MONITORS

• The sequence of steps involved in dynamic
  debugging of a program is as follows
• The user complies the program under the debug
  option. The compiler produces two files- the
  compiled code file the debug information file.
• The user activates the debug monitor indicates
  the name if the program to be debugged .

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DEBUG MONITORS cont

• The debug monitor opens the compiled code debug
  information files for the program.
• The user specifies his debug requirements a
  list of breakpoints actions to be performed at
  breakpoints. The debug monitor instruments the
  program, builds a debug table containing the
  pairs .

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DEBUG MONITORS cont

1. The instrumented program gets control executes
   up to a breakpoints.
2. A software interrupt is generated when the
   ltSI_instrngt is executed. Control is given to the
   debug monitor which consults the debug table
   performs the debug actions specified for the
   breakpoints .

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DEBUG MONITORS cont

• A debug conversation is now opened during
  which the user may issue some debug commands or
  modify breakpoints debug actions associated
  with breakpoints.
• Steps 4 5 are repeated until the end if the
  debug session.

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PROGRAMMING ENVIRONMETS

• A programming environment is a software system
  that provides integrated facilities for program
  creation, editing, execution , testing,
  debugging. It consists of the following
  components
• A syntax directed editor (which is a structure
  editor)
• A language processor a complier, interpreter, or
  both
• A debug monitor
• A dialog monitor