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Operating Systems
Lecture 1
BCS-III
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Computer System1. Hardware
2. Operating system
3. Applications programs
4. Users
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Computer System HardwareComputer System Hardware
Keyboard Mouse
PrinterRAM/ROM
HD
MemBus
System Bus
Monitor
CD
Processor
Floating Point
Unit
Integer
Unit
Cache
Control
Unit
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History of Computer Systems First generation 1945 - 1955
Technology: vacuum tubes, plug boards
Sign up for time, exclusive use of the machine Languages: none
OS: no operating system
Second generation 1955 - 1965 Technology: transistors, punch cards
Mainframes
Languages: FORTRAN, COBOL,
Jobs
OS: batch systems, libraries
Third generation 1965 1980 Technology: Integrated Circuits
Large mainframes and smaller machines (IBM 360 family)
Minicomputers (DEC)
OS: multiprogramming, large systems (multipart), batch and timesharing, emergenceof Unix
Fourth generation 1980 present Technology: Mass production of integrated circuits (chips and boards)
Personal computers/servers/Internet
OS: embedded -> supercomputer, CP/M -> Windows, PARC->Macintosh, Unix -> Linux/Solaris
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What is an Operating System?What is an Operating System?
Sits between programs & hardware
Sits between different programs
Sits betweens different users
But what does
it do?to provide an orderly and controlled allocation of
the processors, memories and I/O devices
among the various programs competing for them
Real Lif
e Example:Government
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Operating system interface
Hardware
OperatingSystem
Software
ComputerUser
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Operating System Goals
Accept input from input devices
Sends output from input devices
Execute user programs and make solvinguser problems easier.
Make the computer system convenient to
use. Use the computer hardware in an efficient
manner.
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Components of Operating System
Process management
Memory management
Secondary management I/O System
File System
Protection System Command interpreter system
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Operating system types
Single user
Multi user
Batch processing
Multiprogramming Time sharing
Real time system
Distributed system
Client server system Handheld
Embedded
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Single User Systems
Personal computers computer system dedicated to asingle user.
Interactive
User convenience and responsiveness.
Can adopt technology developed for larger operatingsystemsmulti-process, multi-user
Individuals usually have sole use of computer and do notneed advanced protection features.
They are popularly associated with Desk Top operatingsystem which run on standalone systems where no useraccounts are required.
Example: DOS
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Multi-User Systems:
Provides regulated access for a number of users bymaintaining a database of known users.
Refers to computer systems that support two ormore simultaneous users.
Another term formulti-useris time sharing.
Ex: All mainframes and are multi-user systems.
Example: Unix
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Batch Processing: In Batch processing same type of jobs batch (BATCH- a set of
jobs with similar needs) together and execute at a time.
First rudimentary system.
User{ operator
R
educe setup time by batching similar jobs Automatic job sequencing automatically transferscontrol from one job to another.
Resident monitor :
initial control in monitor
control transfers to job
when job completes
control transfers back to monitor
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Batch Processing (Contd):
The OS was simple, its major task was to transfer controlfrom one job to the next.
The job was submitted to the computer operator in formof punch cards. At some later time the output appeared.
The OS was always resident in memory. (Ref. Fig. )
Common Input devices were card readers and tapedrives.
Common output devices were line printers, tape drives,and card punches.
Users did not interact directly with the computer systems,but he prepared a job (comprising of the program, thedata, & some control information).
Advantage: Computer operator load data only oneoperation
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Examples
Payroll Systems
Tax systems
Production of electricity Bills National Insurance contributions
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Multiprogramming:
Multiprogramming is a technique to execute number ofprograms simultaneously by a single processor.
In Multiprogramming, number of processes reside in mainmemory at a time.
The OS picks and begins to executes one of the jobs in themain memory.
If any I/O wait happened in a process, then CPU switchesfrom that job to another job.
Hence CPU in not idle at any time.
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Multiprogramming (Contd):
OS
Job 1
Job 2
Job 3
Job 4
Job 5
Figure dipicts the layout of
multiprogramming system.
The main memory consists of 5
jobs at a time, the CP
U executesone by one.
Advantages:
Efficient memory utilization
Throughput increases
CPU is never idle, so
performance increases.
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OS Features Needed
for Multiprogramming SPOOLing (Simultaneous Peripheral
Operation On-Line)
Memory management
CPU scheduling
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Time Sharing Systems:
Time sharing, or multitasking, is alogical extension of multiprogramming.
Multiple jobs are executed by switchingthe CPU between them.
In this, the CPU time is shared bydifferent processes, so it is called asTime sharing Systems.
Time slice is defined by the OS, forsharing CPU time between processes.
Using multiprogramming to handlemultiple interactive jobs
Multiple users simultaneously accessthe system through terminals.
A job is swapped in and out of memoryto the disk if needed.
Examples Airline booking Systems
Process 1 Process 2 Process 3
OS
CPU
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Real-time Systems Well-defined fixed-time constraints. Often used as a control device in a dedicated application such as
controlling scientific experiments, medical imaging systems,industrial control systems, and some display systems.
System is automatically updated when a change is made due totransaction occur.
The terminals must be connected to the computers. Must be an online system.
Medical imaging systems
Industrial control systems
Traffic Lights
Robots
Flight Simulations
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Real-time Systems types
Hard real-timesystems: Secondary storage limited or
absent, data stored in shortterm memory, or read-onlymemory (ROM)
No virtual memorytimecannot be wasted ontranslation of logical to physicaladdresses
OS code structured for
efficiency Plane landing systems, proces
control in nuclear power plants,respirators, etc.
Soft real-timesystems Output should be produced
within the given time
constraints but if it is not,the result is not lifethreatening
Useful in applications(multimedia, virtual reality)requiring advancedoperating-system features.
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Distributed Systems
Distribute the computation amongseveral physical processors.
Loosely coupled system (clusters?)each processor has its own localmemory; processors communicate withone another through various
communications lines, such as high-speed buses , cross-bar switches,LANS, or telephone lines.
Advantages of distributed systems. Resources Sharing
Computation speed up load sharing
Reliability
Communications Disadvantages: control and OS
functions complicated, anddistributing an algorithm over thenodes is difficult.
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Client Server Systems
In which cooperation and intercommunication
between the various elements of a network is
conducted.
In a client server system, application programsresides in server connected to the LAN.
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Handheld Systems
Personal Digital Assistants (PDAs)
Cellular telephones
Issues:
Limited memory
Slow processors
Small display screens.
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Embedded system
Different electronic devices are controlled
Permanently store on Rom chip
Uses Mobile phone Microwave
TV sets
Examples Palm OS
Window CE