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Chapter 5 System Softwares. Hardware. Introduction. User interface: Virtual machine:. System softwares. System softwares: A collection of computer programs that manage the resources of a computer and facilitate access to those resources. User. Virtual machine interface. Virtual machine.

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introduction

Hardware

Introduction
  • User interface:
  • Virtual machine:
system softwares
System softwares
  • System softwares:
    • A collection of computer programs that manage the resources of a computer and facilitate access to those resources

User

Virtual machine interface

Virtual

machine

System softwares

Actual machine interface

Hardware

system softwares1
System 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

Memory

managers

Info.

managers

Scheduler

utility

database systems

text editor

file systems

assembler

compilers

loaders

linkers

...

types of system software
Types 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 mass 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
assembler and assembly language
Assembler and assembly language
  • Machine language:
    • use binary
    • allow only numeric memory addresses
    • difficult to change
    • difficult to create data
  • Assembly language:

assembly

language

program

machine

language

program

assembler

Loader

loaded into

memory

results

Hardware

assembly language
Assembly 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

assembly language1
Assembly language
  • Sample assembly language instruction set:

op-code mnemonic meaning

0000 load X con(X) -> R

0001 store X R -> con(X)

0010 clear X 0 -> con(X)

0011 add X R + con(X) -> R

0100 increment X con(X) + 1 -> con(X)

0101 subtract X R - con(X) -> R

0110 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 = ON

1000 jump X transfer to location X

1001 jumpgt X transfer to location X if GT = ON

1010 jumpeq X transfer to location X if EQ = ON

1011 jumplt X transfer to location X if LT = ON

1100 jumpneq X transfer to location X if EQ=OFF

1101 in X input an integer from standard input

device and store in location X

1110 out X output the value in location X

1111 halt stop program execution

example
Example

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
assembler
Assembler
  • 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
operating system
Operating system

user

user

Input-

Output

storage

Operating system

Hardware

operating system1
Operating 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
events in execution
Events in execution

User

User

User

command center

Scheduler

Resource allocator

Dispatcher

Hardware

Execution

time sharing
Time sharing
  • Multiuser systems

User

User

Machine

User

User

time cycle

A

C

B

A

C

B

scheduling
Scheduling
  • 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