Computers4 Ch2

• 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