Computer Science/Ch. 5 System Softwares5-1

Chapter 5Chapter 5

System SoftwaresSystem Softwares

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IntroductionIntroduction

• User interface:

• Virtual machine:

Hardware

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System softwaresSystem softwares

• System softwares:– A collection of computer programs that manage the resource

s of a computer and facilitate access to those resources

Hardware

System softwares

User

Actual machine interface

Virtual machine interface

Virtualmachine

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System softwaresSystem softwares

• Role of System softwares:– Hide from user details of the internal structure of machine

– Present important information in a way that is easy to understand

– Allow the user to access computing resources in a simple and efficient way

– Provide a secure and safe environment in which to operate

• Types of system softwares:

Operating systems

Language translator

Memorymanagers

Info.managers

Scheduler

utilit

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Types of system softwareTypes of system software

• Language translator:– assembler

– compiler

• Memory managers:– allocate memory space for programs and date and load

programs into memory prior to execution

• File system:– handle the storage and retrieval of information on mas

s storage devices such as disks, CD-ROMs, and tapes

• Scheduler:– Keeps a list of programs ready to run on the processor

and selects the one that will execute next

• Utilities:– library routines that provide useful services to either a

user or other system routines

– text editor

– debugging tools

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Assembler and assembly Assembler and assembly languagelanguage

• Machine language:– use binary

– allow only numeric memory addresses

– difficult to change

– difficult to create data

• Assembly language:

assemblylanguageprogram

assemblermachinelanguageprogram

Loader

loaded intomemory

Hardwareresults

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Assembly languageAssembly language

• Advantages of using assembly language:– Use of symbolic operation codes rather than numeric ones

– Use of symbolic names rather than numeric memory addresses

– Pseudo-operations that provide useful user-oriented services such as data generation

• Sample assembly language:– format:

• Example:

jump loop

.

.

.

loop: load X

• Data generation:

five: data 5

negseven: data -7

lable: op-code mnemonic address field

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Assembly languageAssembly language

• Sample assembly language instruction set:

op-code mnemonic meaning

0000 load X con(X) -> R0001 store X R -> con(X)0010 clear X 0 -> con(X)0011 add X R + con(X) -> R0100 increment X con(X) + 1 -> con(X)0101 subtract X R - con(X) -> R0110 decrement X con(X) - 1 -> con(X)0111 compare X if con(X) > R then GT= ON if con(X) = R then EQ = ON if con(X) < R then LT = ON1000 jump X transfer to location X1001 jumpgt X transfer to location X if GT = ON1010 jumpeq X transfer to location X if EQ = ON1011 jumplt X transfer to location X if LT = ON1100 jumpneq X transfer to location X if EQ=OFF1101 in X input an integer from standard input device and store in location X1110 out X output the value in location X1111 halt stop program execution

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ExampleExample

load B

add C

subtract SEVEN

store A

.

.

.

A: data 0

B: data 0

C: data 0

SEVEN:data 7

• Exercise:– write an assmbly program to compute the sum of

1+3+5+...+99

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AssemblerAssembler

• Assembler's jobs:– convert symbolic op codes to binary

– convert symbolic addresses to binary

– put the translated instructions into a file for future use

• Two-pass assembler:– first pass:

» symbol table

– second pass:

» translate source program into machine language

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Operating systemOperating system

Hardware

Operating system

user user

storageInput-Output

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Operating systemOperating system

• Functions of OS:– user interface

– program scheduling and activation

– system and file access control

– efficient resource allocation

– deadlock detectionand error detection

• deadlock:– Example:

» Program A Program B

» get tape driver get laser printer

» get laser printer get tape driver

» print the file print the file

– deadlock prevention

» if a program cannot get all resources it needs, it must give up all resources it currently owns and issue a completely new request

– deadlock recovery

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Events in executionEvents in execution

User

User Usercommand center

Scheduler

Resource allocator

Dispatcher

Hardware Execution

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Time sharingTime sharing

• Multiuser systems

User

User

User

User

Machine

A B C A B C

time cycle

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SchedulingScheduling

• CPU burst time:– Actual CPU time for a job in its time period

• Scheduling algorithms– First-In-FIrst-Out (FIFO): FCFS

– Shortest Job First (SJF)

– Round Robin (RR)

• Classes of scheduling algorithms:– Nonpreemptive

» do nor allow a job to be stopped once its CPU burst starts

– Preemptive