System Programing Unit 1

Introduction
• What is System?
System is the collection of various
components
Ex:- College is a system
• What is Programming?
Art of designing and implementing the
programs.

What is Software ?
• Software is collection of many programs
• Two types of software
– System software
These programs assist general use application
programs
Ex:- Operation System , Assembler etc.
– Application software
These are the software developed for the specific
goal

• System Program:-
“These are programs which are required for
the effective execution of general user
programs on computer system.”
• System Programming:-
“ It is an art of designing and implementing
system programs.”

Components of System Programming
• Interpreter
• Assembler
• Compiler
• Macros and Microprocessors
• Formal systems
• Debugger
• Linkers
• Operating system

Need Of System Software

The basic need of system software is to achieve the
following goals :-

• To achieve efficient performance of the system
• To make effective execution of general user
program
• To make effective utilization of human resources
• To make available new, better facilities

Operating System
• It is the collection of system programs which
acts as an interface between user and the
computer and computer hardware.
• The purpose of an operating system is to
provide an environment in which A user can
execute programs in a convenient manner

Functions of Operating System

• File handling and management.
• Storage management (Memory management).
• Device scheduling and management.
• CPU scheduling.
• Information management.
• Process control (management).
• Error handling
• Protecting itself from user & protecting user from
other users.

Translators
• These are the system programs that converts
the source program into computer
understandable fashion
• Types of translators
– Single Pass translator
– Multi Pass translator

Translators
• Assembler:-
• These are the system programs which will
automatically translate the assembly language
program in to the machine language program

Source program Target program /
Assembly Lang. Assembler M/C Lang. Prog.
Prog.

Database

Translators
• Complier:-
• These are the system programs which will
automatically translate the High level language
program in to the machine language program

High level Lang. Compiler M/C Lang. Prog.
Prog.

Database

Translators
• Cross Assembler:-
• These are the system programs which will automatically
translate the Assembly Language program compatible with
M/C A, in to the machine language program compatible with
M/C A, but the underlying M/C is M/C B
Assembly Lang. Cross Assembler M/C Lang. Prog.
Prog. Compatible Compatible with
with M/C A M/C A

M/C B

Translators
• Cross Compiler:-
• These are the system programs which will automatically
translate the HLL program compatible with M/C A, in to the
machine language program compatible with M/C A , but the
underlying M/C is M/C B
HLL Prog. Cross Compiler M/C Lang. Prog.
Compatible with
M/C A

M/C B

Translators
• Interpreter
– It is the language translator which execute source
program line by line with out translating them into
machine language.
Types of Interpreter
– Pure Interpreter
• In this case no preprocessing is required on source
program before an interpretation starts.
• Some preprocessing is required on source program
before an interpretation starts.

Loader
• A Loader is system program that place the
object program into main memory and
prepares it for execution.
• Basic functions of loader
– Allocation
– Linking
– Relocation
– Loading

Types of Loader
• Compile-and-go Loader
• Relocating Loader
• Direct Linking Loader
• Absolute Loader
• General Loader
• Dynamic Loader

Macro & Macro processor
• Macro
– Macro is a single line abbreviation for a group of instruction.

MACRO --------Start of definition
INCR -------- Macro name
A 1,DATA
A 2,DATA Sequence of instructions to
be abbreviated.
A 3,DATA
MEND -------- End of definition

Linking and Linker
• Linking
– The Process of merging many object modules to
form a single object program is called as linking.
• Linker
• The Linker is the software program which binds
many object modules to make a single object
program.

Formal System
• A formal system is an un interpreted calculus.
It consists of
– Alphabets
– A set of words called Axioms.
– Finite set of relations called rules of inference or
production rules.
– Ex Boolean algebra.

Types of Assembly Language
statements
• Imperative statements
–An imperative statement in assembly
language indicates the action to be
performed during execution of
assembly statement
Ex:- A 1,FOUR

• Declarative Statement:-
– These statements declares the storage area or
declares the constant in program.

– EX A DS 1
ONE DC “1”

• Assembler Directives
– These are the statements used to indicate certain
thing regarding how assembly of input program is
to be performed.

– Ex START 100
USING *, 15

Types of Assembler
• Single pass Assembler

• Multi pass Assembler

Problem of Forward Reference
• When the variables are used before their
definition at that time problem of forward
reference accurse.

Problem of Forward Reference
JOHN START 0
USING *, 15
L 1, FIVE
A 1,FOUR
ST 1, TEMP
FOUR DC F’4’
FIVE DC F’5’
TEMP DS 1F
END

General Design Procedure of Two Pass
Assembler
1. Specify the problem
2. Specify data structures
3. Define format of data structures
4. Specify algorithm
5. Look for modularity [capability of one
program to be subdivided into independent
programming units.]
6. Repeat 1 through 5 on modules.

SOURCE PROGRAM FIRST PASS SECOND PASS
RAM START 0
USING *, 15
L 1, FIVE 0 L 1,_(0,15) 0 L 1, 16(0,15)
A 1,FOUR 4 A 1,_(0,15) 4 A 1, 12(0,15)
ST 1, TEMP 8 ST 1,_(0,15) 8 ST 1, 20(0,15)
FOUR DC F’4’ 12 4 12 4
FIVE DC F’5’ 16 5 16 5
TEMP DS 1F 20 -- 20 --
END

Specify the problem
Pass1: Define symbols & literals.
1) Determine length of m/c instruction [MOTGET1]
2) Keep track of Location Counter [LC]
3) Remember values of symbols [STSTO]
4) Process some pseudo ops[EQU,DS etc] [POTGET1]
5) Remember Literals [LITSTO]

Pass2: Generate object program
1) Look up value of symbols [STGET]
2) Generate instruction [MOTGET2]
3) Generate data (for DS, DC & literals)
4) Process pseudo ops[POTGET2]

Step 2. Data structure:-

Pass1: Databases
• Input source program
• “LC” location counter used to keep track of each
instructions addr.
• M/c operation table (MOT) [Symbolic mnemonic & length]
• Pseudo operation table [POT], [Symbolic mnemonic &
action]
• Symbol Table (ST) to store each lable & it’s value.
• Literal Table (LT), to store each literal (variable) & it’s
location.
• Copy of input to used later by PASS-2.

Step 2. Data structure:-

• Pass2: Databases
• Copy of source program input to Pass1.
• Location Counter (LC)
• MOT [Mnemonic, length, binary m/c op code, etc.]
• POT [Mnemonic & action to be taken in Pass2
• ST [prepared by Pass1, label & value]
• Base Table [or register table] indicates which registers
are currently specified using ‘USING’ pseudo op & what
are contents.
• Literal table prepared by Pass1. [Lit name & value].

Format of Data Structures
• Machine Operation Table
– The op-code is the key and it’s value is the binary
op code equivalent, which is used for use in
generating machine code.
– The instruction length is stored for updating the
location counter.
– Instruction format is use in forming the m/c
language equivalent

Symbol table & Literal table:-

Machine Dependent and Machine
Independent features of Assembler
• M/C Dependent Features
– A] Instruction format & addr. mode:-
– B] Program Relocation
• Machine Independent Assembler Features
– 1) Literals
– 2) Symbol defining statements
– 3) Expressions

System Programing Unit 1

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System Programing Unit 1