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Operating Systems
Certificate Program in Software Development
CSE-TC and CSIM, AIT
September -- November, 2003
1. Introduction
(Chapter 1, S&G)
 Objectives
– introduce Operating System (OS) principles
OSes: 1. Intro
1
Contents
1. What is an OS?
2. Some History
– early systems, batch systems,
multiprogramming, time-sharing,
desktop systems
3. Recent Trends
– multiprocessor systems, distributed,
clustered, real-time, handheld, etc.
OSes: 1. Intro
2
1. What is an OS?
User 1
User 2
compiler
editor
…..
…..
User N
database
Application Programs
Operating System
Computer Hardware
OSes: 1. Intro
3
Features
 An
OS is a program that acts as an
intermediary between users and hardware
– supports a high-level work environment
– makes hardware convenient to use
– makes efficient use of hardware
 OS
OSes: 1. Intro
design goals are often contradictory
continued
4
 The
OS manages resources
– e.g. CPU time, memory, files, I/O devices
– avoid bottlenecks
– keeps the hardware busy
 The
OS controls
– prevents users/programs adversely affecting the
hardware or other users
– the system should never crash
OSes: 1. Intro
5
OS Development
OSes: 1. Intro
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2. Some History
 2.1.
 2.2.
 2.3.
 2.4.
 2.5.
OSes: 1. Intro
Early Systems
Batch Systems
Multiprogramming Batch Systems
Time-Sharing
Desktop Systems
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2.1. Early Systems
 One
person at a contol panel of switches
and lights
 Load libraries/utilities from tape
 Slow set-up
 Very costly hardware
Read
Compute
Print
Read
OSes: 1. Intro
Compute
Print
8
2.2. Batch Systems
 Motivation:
highly utilise the hardware
– dedicated computer operator
– card/tapes handed to the operator
 Similar
jobs were run in sequence (batched)
– no machine/user interaction
– errors were recorded as a printed core dump
– very slow turnaround time (for users)
OSes: 1. Intro
9
Resident Monitor
 For
automatic job sequencing
Loader Job Sequencing
Control Card
Interpreter
User Program Area
monitor
OSes: 1. Intro
10
Control Cards
 User’s
cards included control cards to guide
the monitor.
$END
data cards
$RUN
program cards
$JOB
OSes: 1. Intro
11
Off-line I/O Processing
On-line:
Card Reader
CPU
Line Printer
Off-line:
CPU
Card Reader
OSes: 1. Intro
tape drives
Line Printer
tape drives
12
Spooling
 Job
pool on disk, scheduled by OS
disk
I/O
Card Reader
OSes: 1. Intro
CPU
Line Printer
13
Benefit Of Spooling
Read
OSes: 1. Intro
Compute
Print
Read
Compute
Print
Read
Compute
Print
14
2.3. Multiprogrammed Batch Systems
 Have
several jobs in memory at a time.
 Multiprogramming
allows the OS to switch to
executing another job when the current one is
suspended (e.g. waiting for user input).
 The
OS may also swap jobs to/from disk.
 Requires
OSes: 1. Intro
CPU scheduling
15
2.4. Time-Sharing
 Multiple
jobs are executed by the CPU
switching between them
– as in multiprogramming
 Difference
is speed; the switching is so fast
that users feel that their programs are
always running.
 Executing
OSes: 1. Intro
program is called a process.
continued
16
 Virtual
memory
– hides the distinction between memory and disk
 Disk
management
 Concurrent
execution requires fancy
scheduling schemes
 Job
synchronisation, communication,
deadlock avoidance
OSes: 1. Intro
17
2.5. Desktop Systems
 Personal
computers
– computer system dedicated to a single user
 I/O
devices
– keyboards, mice, display screens, small printers
 User
OSes: 1. Intro
convenience and responsiveness
continued
18
 Can
adopt technology developed for larger
operating system
– sole use means less need for protection features
 May
run several different types of operating
systems
– e.g. Windows, MacOS, UNIX, Linux
OSes: 1. Intro
19
3. Recent Trends
3.1.
3.2.
3.3.
3.4.
3.5.
3.6.
OSes: 1. Intro
Multiprocessor Systems
Distributed Systems
Clustered Systems
Real-time Systems
Handheld Systems
Computing Environments
20
3.1. Multiprocessor Systems
 A system
with more than 1 processor, but
perhaps sharing computer bus, clock,
memory and devices
– tightly coupled systems
n
OSes: 1. Intro
processes = n times speed-up
continued
21
 Benefits:
– save money on hardware
– increased reliability (graceful degradation)
 Two
main types:
– symmetric multiprocessing systems
– asymmetric multiprocessing systems
OSes: 1. Intro
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3.1.1. Symmetric Multiprocessing
 Each
processor runs an identical copy of
the OS
 Often
in a master-slave configuration
 Jobs/resources
are shared dynamically
for better load balancing
OSes: 1. Intro
23
3.1.2. Asymmetric Multiprocessing
 Have
– e.g.
OSes: 1. Intro
dedicated processors for specific tasks
remote job entry (RJE),
I/O terminal buffering
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3.2. Distributed Systems
 “The
OSes: 1. Intro
system is the network.”
continued
25
 Multiprocessors,
but not sharing memory,
clock, etc.
– may be geographically separated
– loosely coupled systems
 Benefits:
– resource sharing, speed-up, reliability
– matches modern business practise
OSes: 1. Intro
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3.3. Clustered Systems
 Clustering
allows two or more systems to
share storage.
– provides high reliability
 Asymmetric
clustering
– one host runs the application while others
standby
 Symmetric
clustering
– all hosts run the application
OSes: 1. Intro
27
3.4. Real-time Systems
 There
are time constraints placed on
operations/data flows which must be met.
 Uses:
– scientific experiments, medicine, industrial
control systems, home appliances, weapons
 Two
OSes: 1. Intro
types:
– hard real-time systems
– soft real-time systems
28
3.4.1. Hard Real-time Systems
 Critical
tasks are guaranteed to be done on
time.
 Many
useful hardware/OS features are
missing since they make the time
constraints too hard to satisfy
– e.g. no secondary storage
OSes: 1. Intro
29
3.4.2. Soft Real-time Systems
 Critical
tasks are given priority, but their
time constraints may not be met.
 Weaker,
but can be used alongside typical
OS features
 Applications: VR,
OSes: 1. Intro
multimedia
30
3.5. Handheld Systems
 Personal
Digital Assistants (PDAs)
 Cellular telephones
 Issues:
– limited memory
– slow processors
– small display screens
OSes: 1. Intro
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3.6. Computing Environments
 Changing
environments are leading to
changes in OS requirements
–
–
–
–
OSes: 1. Intro
traditional
hand-held, mobile
Web-based
embedded, dedicated processors
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