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CE01000-6 Operating Systems
Lecture 1Introduction to the module,
definition and historical development of operating systems
Who am I?Module Leader.
Ian Sunley, Room: K340, phone:353418, e-mail:
You will also be taught by:
Mohammad Hasan, Room: K216, phone:353466, e-mail: [email protected]
Classes 2 lectures a week –
Thursday 09:00 Lecture Theatre 2 (Blue) and for the First 2 weeks 14:00 Friday Lecture Theatre 3 (Green) and then for the rest 15:00 Thursday Lecture theatre 2 (Blue)
Typically one covering theory and the other giving a practical illustration in Windows and Unix
2 hour tutorial/practical each week – in K104 go through theory questions and do some
practical exercises on example operating systems (Windows & Linux)
Assessment
Class test – in last lecture of week 12 – worth 30% of marks
Portfolio of weekly tutorial and practical work – worth 70% of marks
Portfolio coursework
Each week you will get some tutorial/practical exercises to do.
The following week I will make available answers to selected exercises
However, some of the tutorial and/or practical exercises that you get will be used for the portfolio (and so there will be no example answers)
Portfolio (continued)
On the Friday of week 12 (23rd November) you will have to submit the exercises that are to be marked in a folder to the Faculty General office as your coursework.
I will only tell you which of the weekly exercises are the ones to be included in the portfolio, sometime after the exercises have been set – so you have a chance to do all the exercises.
Blackboard
PowerPoint of lecture slides, the tutorial & practical exercises and example answers to the selected exercises will be available on Blackboard
http://staffs.blackboard.com Login using your user id. and password Go to CE01000-6 Operating Systems and then
Module Study Space Also announcements, assessment information
and other general information
Operating Systems Reading
Operating systems theory – recommended book: Operating System Concepts, A. Silbershatz,
P. B. Galvin and G. Gagne, 8th edition, Wiley, 2008
Many tutorial questions are taken from this book
Windows – recommended book to read if you are interested: Microsoft Windows Internals, M.E.Russinovich
and D.A.Solomon, 4th edition, Microsoft Press, 2005
Linux – recommended book to read if interested: Operating Systems with Linux, J. O’Gorman,
Macmillan, 2001
Study time guide Formally a module has a total of 150 hours
allocated to it as: 48 hours lectures/tutorials/practicals
(including 1 hour for test in last lecture) leaving 102 hours left over which could be
organised by yourself as:
20 hours revision for the test
82 hours for work on tutorial/practical exercises and weekly reading = almost 6 hours of reading and independent study per week
Overview of rest of lecture
In the rest of this lecture we will be looking at:
1. What is an operating system? definition and goals of operating systems
2. How did operating systems develop historically to become what they are today? Outline of the historical development of operating systems
Operating system - definition
An operating system is a program that acts as an intermediary between a user of a computer or developer of application programs (and the application programs themselves) and the computer hardware.
Computer hardware + operating system = usable machine
Goals of an operating system
To maximise utilisation of the hardware resources
sharing the hardware resources efficiently among different user programs
To maximise the productivity of users using the system by maximising the usability of the system presenting an easy to use interface for managing data and
program execution To provide a system call interface
for software developers to use eliminating need for application programmers to write their
own software to manipulate hardware.
So operating systems are needed to make any computer usable as a tool
The question is how did people come to develop this large piece of software that we all take for granted (until something goes wrong).
So where did everything start? You need to refer to additional sheet on typical
sequence of operation of a computer at different stages in OS development
Early Systems – Bare machine (early 1950s)
Structure Large machines (filling a room) run from a single
console or panel (often using wired plugs like old fashioned telephone exchange)
Single user system - Programmer/User was the person responsible for complete operation of machine
Paper tape or punched cards provide all I/O Look at table in supplementary sheet to see
typical operation
Early Software - assemblers, compilers, linkers, loaders + device drivers
Secure – no viruses/worms, hacking, networks, etc
Inefficient use of very expensive resources (> €100- €200 million at current money values) Significant amount of setup time Low CPU utilization (< 1% of time actually running)
So need really to increase efficiency!!!!
Simple Batch Systems
Increase efficiency by: Hiring an operator to run machine User no longer had ANY direct contact with the
computer (everything done via submission of jobs to operator who actually used the computer)
Reduce setup time by loading jobs together that have similar requirements e.g. all jobs that need compiler loaded together – known as batching (set of similar jobs are a batch)
Use of resident monitor (see next slide) Typical operation – see table in supplementary sheet
Resident monitor
Automatic job sequencing – automatically transfer control from one job to another. This lead to first rudimentary operating system known as a resident monitor.
Resident monitor operation: initial control in monitor loads a job control transfers to loaded job to run when job completes control transfers back to monitor
Simple Batch Systems (Cont.)
Problems with simple batch systems:
1. How does the monitor know about the nature of the job (e.g., Fortran compilation versus Assembly) or which program to execute?
2. How does the monitor distinguish (a) one job from another job? (b) data from program?(Remember programs and
data just punched holes on cards or paper tape – so how know?)
Solution - introduce control cards
So resident monitor had to include: Control card interpreter – responsible for reading
and carrying out instructions on the cards. Loader – loads systems programs and
applications programs into memory. Device drivers – know special characteristics
and properties for each of the system’s I/O devices and input/output from/to devices e.g. card reader.
Evolution of resident monitor
Monitor Problems
Problem with resident monitors: Slow Performance – I/O and CPU could not overlap;
card reader very slow. Solution:
Off-line operation (not connected to main computer) – can speed up computation by loading jobs into memory on-line from magnetic tapes rather than directly from card readers
Card reading and line printing to/from magnetic tapes then done off-line using small (much cheaper) satellite processor/computer.
Batch with Off-Line Operation
Tape Drives
Off-Line Operation (Cont.)
Advantage of off-line operation – main computer not constrained by the speed of the card readers and line printers, but only by the speed of much faster magnetic tape units.
No changes need to be made to the application programs to change from direct to off-line I/O operation.
Real gain – possibility of using multiple reader-to-tape and tape-to-printer systems for one CPU.
Spool = Simultaneous Peripheral Operation On-Line
Spooling overlaps I/O of one job with computation of another job while connected to main computer by using a hard disk.
In spooling, the OS, while executing one job: reads next job from card reader into a storage area
on the disk (job queue/pool) using an I/O channel. outputs printout of previous job from disk (spool area
on disk) to printer via an I/O channel.
Batch with Spooling
Job pool – is a data structure that allows the OS to select which job to run next in order to increase CPU utilization.
Spooling is a significant improvement over off-line operation.
See table in supplementary sheet for typical operation
Spooling
Multiprogrammed Batch Systems
Growth in size of main memory meant that job pool and several jobs could all be held in main memory. This lead to:
Multiprogramming = Several jobs are kept in main memory at the same time, and the CPU is multiplexed (switched) between them. So that when one job is idle, rather than leaving
CPU idle, the OS can switch to running a different job
OS Features Needed for Multiprogramming
To provide multiprogramming facility OS now needs to perform:
1. I/O – I/O now performed by the OS rather than individual application program doing it directly
2. Memory management – the system must allocate the memory to several jobs and prevent one job from interfering with memory allocated to another.
3. CPU scheduling – the system must choose which among several jobs to run (from those that are ready to run)
4. Resource allocation of such things as I/O devices to jobs.
Operation of multiprogramming – see table on supplementary sheet
Time-Sharing Systems
Introduction of terminals with keyboards and simple monochrome VDU displays meant that users could now communicate directly with running computer and not just indirectly via a computer operator.
Time-Sharing Systems (Cont.) 2 features of Time-sharing systems:
1.The CPU is multiprogrammed/multiplexed among several jobs that are kept in memory and on disk - jobs may be swapped to/from main memory and disk (as before)
2. On-line communication between the user and the system is provided (Interactive computing)
when the operating system finishes the execution of one command, it seeks the next “control statement” not from a card reader, but rather from the user’s keyboard.
Low turnaround time (quick response to user) is desirable
Jobs (user programs and data) now need to be on-line for user to be able to submit to system to run i.e. there must now be an on-line file system held on the disk.
Time-Sharing Systems (Cont.)
Personal-Computer Systems
Come full circle in development -> personal computers – computer system dedicated to a single user (as were first computers)
I/O devices – keyboards, mice, display screens, small printers, others (game controllers, etc.).
User convenience and responsiveness is primary goal, not efficient utilisation of hardware
Sequence of operation of a computer at different periods in OS
evolutionBare machine
setup Load program Input – process – output(cards) (printer)
Tear down
Simple batch
setup Load program Input – process – output(cards) (printer)
Input – process – output(cards) (printer)
Input – process – output(cards) (printer)
Tear down
Batch with Off-Line satellite processors
setup Load program(Mag. Tape)
Input – process – output(Mag. Tape) (Mag Tape)
Input – process – output(Mag. Tape) (Mag Tape)
Input – process – output(Mag. Tape) (Mag Tape)
Tear down
Satellite processor
Input from cards to Mag tape
Output from Mag tape to printer
Batch with Spooling – Simultaneous Peripheral Operation On-Line
Bootup – from disk
Standard programs permanently resident on disk.Jobs for programs to do submitted to system from cards to form job pool
Job 1 – Input – process– (disk) Job 2 - Input – (disk) Job 3
output(disk)process – output (disk)Input – process – output(disk) (disk)
I/O Channel Input from cards to Disk
Output from Disk to printer
Mutli-programmed
“ Several jobs from job pool on disk held in main memory at the same time
Processor switches between jobs when current job needs to wait for I/O from disk
I/O channel as above
Time-sharing (Interactive and multi-programmed)
Programs but also much data held permamently on disk (in file system on disk). Jobs submitted to system from terminal.
Several jobs from job pool on disk held in main memory at the same time.
Processor switches between jobs when current job needs to wait for I/O from disk or current job gets interupted after a fixed time quantum has expired – to give interactive users speedier response
Input from terminals as well as cards, etc,
Output to VDU screens as well as printers
I/O Channel as before
Computer operation and OS evolution (continued)
References
Operating System Concepts. Chapter 23. Also see supplementary sheet summarizing
typical sequence of operation of computer at different periods of operating systems development
