K.K. WAGH POLYTECHNIC, NASHIK-03 DEPARTMENT OF COMPUTER TECHNOLOGY

(Second Shift)

Chapter-01

Introduction to

System Programming

System Software consists of a variety of programs that

support the operation of a computer.

The software makes it possible for the users to focus

on an application or other problem to be solved,

without needing to know the details of how the

machine works internally.

A System program is a program which is required for

the effective execution of a general user (application)

program.

The term execution here includes all activities namely

writing program code ,editing, storage, translation,

relocation, linking and eventual execution.

System Software

System Programs

Operating

System

Hardware

Application Programs

Hierarchy of computer

components

System Software

Components of System Software

Assembler

Linker

Loader

Macro processor

Text editor

Compiler

Operating system

Debugging system

Source Code Control System

1. Assemblers:

Programmers found it difficult to write or read programs in

machine language, so for more convenience they began to use a

mnemonic for each machine instruction, which subsequently

translate into machine language.

Such a mnemonic machine language is now called as an

assembly language. Program known as assembler were written to

automate the translation of assembly language into machine

language.

The input to an assembler is an assembly language program.

Output is an object program plus information that enables the loader

to prepare the object program for information.

Evolution of System Software

Evolution of System Software

2. Loaders :

Once the assembler produces an object program, that program

must be placed into memory and executed. It is the purpose of the

loader to assure that object program are placed in memory in an

executable form.

A loader is a program that places programs into main memory

and prepares them for execution.

There are various loading schemes: absolute, compile-and-go,

relocating, ,dynamic linking and direct-linking. In general loader

must load, relocate, and link the program.

The period of execution of user’s program is called execution

time. The period of translating a user’s program is called assembly or

compile time. The period of loading and preparing an object program

for execution is called load time.

Evolution of System Software

3. Macros:

To avoid the repetition of the identical parts of code in a program

operating system provide a macro processing facility, which permits

the programmer to define an abbreviation for a part of his program

and to use the abbreviation in his program.

The macro processor treats the identical parts of the program

defined by abbreviation as a macro definition.

The macro processor substitutes the definition for all occurrences

of the abbreviation (macro call) in the program.

Evolution of System Software

4. Compilers:

A compiler is a program that accepts a program written in high

level language and produce an object program.

e.g. FORTRAN, COBOL, C etc.

Modern compilers must interact closely with the operating

system to handle statements concerning the hardware interrupts of a

computer system.

Evolution of System Software

5. Operating Systems:

An operating system is an interface between user and computer

hardware.

An OS is concerned with the allocation of resources and services,

such as memory, processors, devices and information. The OS

includes programs to manage these resources, such as bus controller,

a scheduler, memory management module, I/O programs, and a file

system.

Evolution of Operating System

Historical Review of Operating Systems:

1. Monitors-Monitors are the simplest operating systems.

-Single user systems .

-Allow user interaction.

2. Simple Batch Systems-The user prepares a job (which consists of program, data and some

control information), submits it to the computer operator and receives

the output after the program is executed.

-The job is usually punched on cards and the output is usually

printed.

-To speed up processing, jobs with similar needs can be batched

together and run as a group.

-The operating system is always in memory and its job is to transfer

control automatically from one job to the next.

card reader

CPU

I/O line printer

As the I/O devices are slower than the speed of the CPU (the

difference may be three orders of magnitude or more), the CPU is often

idle. For using the system more efficiently, cards can be read from the

card reader onto the disk. The operating system records their location on

disk in a table. When a job requests the printer, the output is copied into a

system buffer and is written to the disk. When the job is completed, the

output is printed. This form of processing is called spooling

(simultaneous peripheral operation on line).

Evolution of Operating System

Evolution of Operating System

3. Multiprogrammed Batch Systems:The operating system keeps several jobs (a subset of jobs in the

job pool) in memory at a time. During the execution of one job, if it

waits for an I/O operation to complete, the operating system switches to

and executes another job. In this way, as long as there is always some job

to execute, the CPU will never be idle.

4. Time-Sharing SystemsIn multiprogrammed batch systems, the user cannot interact with

the program during its execution. In time-sharing or multitasking

systems, multiple jobs are executed by the CPU switching between them,

but the switching occurs so frequently that the user may interact with

each program while it is running. Time-sharing operating systems:

-uses CPU scheduling and multiprogramming,

-uses time-slice mechanism,

-allows interactive I/O,

-allows many users to share the computer simultaneously.

Evolution of Operating System

5. Real time operating systems:

Used whenever a large number of external events have to be treated

in a short or limited interval of time

Support for multiprogramming/multi-tasking

Main goal:

Minimization of the response time to service the external events.

Memory management:

-Concurrent processes are loaded into the memory.

-Support for protection and inter-process communication.

I/O management:

-Critical in time

-Processes dealing with I/O are directly connected to the interrupt

vectors (or handling the interrupt requests)

File management:

It may be missing

If exists, it should comply with requirements for timesharing

systems + it should satisfy the requirements for real time systems

Evolution of Operating System

6. Distributed operating systemsDistributed systems also have more than one processor. Each

processor has its local memory. Processors communicate through

communication lines (eg. Telephone lines, high-speed bus, etc.).

Processors are referred to as sites, nodes, computers depending on the

context in which they are mentioned. Multicomputer systems are loosely

coupled. Example applications are e-mail, web server, etc.

Evolution of Operating System

Foundation of System Programming

Machine Structure

Fig. illustrates the

structure of the

CPU for a typical

von Neuman

machine , such as

the IBM

System/360.

The CPU consists of an instruction interpreter, a location counter, an

instruction register and various working registers and general registers.

Instruction Interpreter:

It is group of electrical circuits(hardware), that execute the

instructions fetched from memory.

Location Counter(LC):

It is also called as Program Counter(PC) or Instruction

Counter(IC), is a hardware memory device which denotes the location of

the current instruction being executed.

Instruction Register(IR):

A copy of current instruction is stored in the Instruction

Register.

Machine Structure

Working & General Registers:

The working registers (WR) are memory devices that serves as

“scratch pads” for the instructions interpreter, while the general

registers(GR) are used by the programmer as storage location and for

special functions.

Memory Address Register(MAR) & Memory Buffer Register(MBR)

The primary interface between the memory and CPU is via the

MAR and MBR.

The MAR contains the address of the memory location that is to

be read from or store into.

The MBR contains a copy of the designated memory location

specified by MAR after a “read” or the new contents of the memory

locations prior “write”.

Machine Structure

Memory Controller:

It is hardware that transfers data between the MBR and primary

memory locations the address of which is in the MAR.

I/O Channel

The I/O channel interpret special instructions for inputting and

outputting information from the memory.

Machine Structure

Thank You