Transcript 5-1 Chapter 5 System Softwares

Chapter 5
System Softwares
Computer Science/Ch. 5 System Softwares
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Introduction
• User interface:
Hardware
• Virtual machine:
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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
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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
Memory
managers
...
text editor
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database systems
file systems
linkers
loaders
compilers
assembler
Computer Science/Ch. 5 System Softwares
Info.
Scheduler
managers
utility
Language
translator
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
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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
assembler
machine
language
program
Loader
loaded into
memory
results
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Hardware
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:
lable: op-code mnemonic address field
• Example:
loop:
jump
loop
.
.
.
load X
• Data generation:
five:
data
5
negseven: data
-7
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Assembly language
• Sample assembly language instruction
set:
op-code mnemonic
meaning
0000
0001
0010
0011
0100
0101
0110
0111
load X
store X
clear X
add X
increment X
subtract X
decrement X
compare X
1000
1001
1010
1011
1100
1101
jump X
jumpgt X
jumpeq X
jumplt X
jumpneq X
in X
1110
1111
out X
halt
con(X) -> R
R -> con(X)
0 -> con(X)
R + con(X) -> R
con(X) + 1 -> con(X)
R - con(X) -> R
con(X) - 1 -> con(X)
if con(X) > R then GT= ON
if con(X) = R then EQ = ON
if con(X) < R then LT = ON
transfer to location X
transfer to location X if GT = ON
transfer to location X if EQ = ON
transfer to location X if LT = ON
transfer to location X if EQ=OFF
input an integer from standard input
device and store in location X
output the value in location X
stop program execution
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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
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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
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Operating system
user
user
InputOutput
storage
Operating system
Hardware
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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
» get tape driver
» get laser printer
» print the file
Program B
get laser printer
get tape driver
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 execution
User
User
command center
Scheduler
Resource allocator
Dispatcher
Hardware
Execution
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User
Time sharing
• Multiuser systems
User
User
Machine
User
User
time cycle
A
B
C
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B
C
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
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