1. Operating Systemand Utility Programs Chapter 2 B.M.H

2. Computer System

Hardware

• Input device

• Processor (CPU)

• Output device

• Storage (secondary storage)

Software

• System SW

• Application SW

People

MIU 3. Learning Objectives

OS for large computer systems

• The method of resource allocation

Utility Programs

MIU 4. Mainframes

Large, fast and fairly expensive computers

Used by business or governmentto provide centralized storage

EX) IBM 4381, 9300, 3090, Cyber 180

MIU 5. MIU 6. OS for large computers

Large computer - mainframes

• Around about twice as long as PCs

• Owned by businesses and universities

• Used by many people at once

• Present special (sharing) problems

• • Program, CPU, memory, storage, printer

OS : take care of these things behind the scenes

• So that User can share the computer s resources

MIU 7. Resource Allocation

Allocated?

• Shared resources

• (Allocate : give something to somebody for special purpose)

Resources allocation

• : the process of assigning computer resources to certain programs

MIU 8. Resource Allocation

Sharinga CPU

Sharinga Memory

SharingStorage Resources

SharingPrinting Resources

MIU 9. Sharing the CPU

Most computers have a single CPU.

• All programs must share it.

The sharing process

• Controlled by the OS

• Two approaches to sharing

• • Multiprogramming

• • Time-sharing

• • Multiprocessing

MIU (Resource allocation) 10. Multiprocessing

The use of a powerful computer withmultiple CPUs

Multiple programs can runsimultaneously , each using its own processor

MIU (Resource allocation) 11. Multiprogramming

Onlyone Central Processing Unit

Two or more programs are executed in the same time frame,concurrently

• But not exactly at the same instant

• Taking turns ; one program runs for a while, and then another one runs

Event-driven

• Programs share resources based on events that take place in the programs.

MIU (Resource allocation) 12. Multiprogramming

Implemented by OS through a system of interrupts

• Interrupts

• • A signal that causes normal program processing to be suspended temporarily.

MIU 13. Time-Sharing

A special case of multiprogramming

Time-driven

• To give each user a time slice

• The OS doesn t wait for completion of an event

• • At the end of the time slice, the resources are taken away from the user and given to someone else

MIU (Resource allocation) 14. Sharing Memory

Memory management

• The process of

• • allocating memory to programs and

• • keeping the programs in memory separate from one another

• Methods

• • Partitions (or regions)

• • Foreground and background

• • Virtual storage

MIU (Resource allocation) 15. Partitions

Some systems simply divide memory into separate areas (partitions or regions)

• Each of which can hold a program

MIU Sharing Memory 16. Foreground and Background

Large all-purposed computers divide the memory into foreground and background

In a time-sharing environment

• Foreground

• • For programs that havehigher priority

• • : Interactive program (with the user at a terminal awaiting response)

• • Receive more CPU time

• Background

• • For programs with less pressing schedules

• • lower prioritiesand less CPU time

MIU Sharing Memory 17. Virtual Storage (1)

Many computer systems uses this technique

Calledvirtual memory

• Virtual : made to appear to exist by the use of computer SW

The programs currently being executed are stored ondisk ,

portions of these programs

• are brought intomemoryas needed.

• Memory : real storage

• Secondary storage : virtual storage

MIU Sharing Memory 18. Virtual Storage (2)

Paging

• one way of virtual storage

• the process of

• • dividing a program into equal-size pieces

• • ; calledpages

• • storing them in equal-size memory spaces

• • ; calledpage frames

• All pages and page frames

• • : the same fixed size (ex. 2 or 4 KB)

MIU Sharing Memory Refer to Fig 2-11 19. Sharing Storage Resources

More than user want to read or write a record

• from the same disk pack at the same time

OS

• Keeps track of which file is where

• Responds to commands to manipulate files

• Keeps track of the Input and output requests

• Processes them

• • In the order in which they were received

• Routes any program instruction to read or write a record

MIU Resource allocation 20. Sharing Printing Resources

Spooling

• A process for sharing a printer

• • Moving data and store it for a short time on adiskbefore it is printed

• • • Each program writes onto a disk each line that is to be printed

• • The disk file is placed into aqueue

• • It is printed when the printer becomes available

MIU Resource allocation 21. Utility Programs File Manager Back up and Restore File Compression Defragmenter Device Drivers 22. Utility Programs (1)

Most of the resource allocation tasks

• : done by the OS without user involvement

Utility Programs

• : perform explicit servicesat the user s request

• Utility : a piece of computer SW that performs a particular task

• Part of the system software, not part of the OS.

• Some utilities are packaged with OSs

• Others can be purchased separately

MIU 23. Utility Programs (2)

To avoid duplication of effort

• Backing up

• Restoring files

• Compressing files and entire hard disks

• Locating files

• Searching computer viruses

MIU 24. File manager (1)

Organize and manage files in a hierarchical directory structure

• organized in a way that makes sense to you

• Directory

• • : a named area in storage that can contain files and other directories

• • The newer versions of Windows