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Transcript
COMP 3500
Introduction to Operating Systems
Overview
Dr. Xiao Qin
Auburn University
http://www.eng.auburn.edu/~xqin
[email protected]
1
Slides adopted from Drs. Abraham Silberschatz, Peter B. Galvin, and Greg Gagne
Four Components of a Computer System
2
Exercise 1: What are operating system goals?
• A program that acts as an intermediary
between a user of a computer and the
computer hardware
• Operating system goals:
– Execute user programs and make solving
user problems easier
– Make the computer system convenient to
use
– Use the computer hardware in an efficient
manner
3
Exercise 2: What do users and
mainframes want from operating
systems, respectively?
•
•
•
•
•
•
•
4
Convenience
Resource utilization
Ease of use
Fast throughput
Short response time
Low cooling cost
Long battery life
What an operating systems does?
• Users want convenience, ease of use and good
performance
– Don’t care about resource utilization
• But shared computer such as mainframe or
minicomputer must keep all users happy
• Users of dedicate systems such as workstations have
dedicated resources but frequently use shared
resources from servers
• Handheld computers are resource poor, optimized
for usability and battery life
• Some computers have little or no user interface, such
as embedded computers in devices and automobiles
5
System View: Operating System
Definition
• OS is a resource allocator
– Manages all resources
– Decides between conflicting requests for
efficient and fair resource use
• OS is a control program
– Controls execution of programs to
prevent errors and improper use of the
computer
6
Operating System Definition (Cont.)
• No universally accepted definition
• “Everything a vendor ships when you order an
operating system” is a good approximation
– But varies wildly
• “The one program running at all times on the
computer” is the kernel.
• Everything else is either
7
– a system program (ships with the operating
system) , or
– an application program.
Computer System Organization
• One or more CPUs, device controllers connect
through common bus providing access to shared
memory
• Concurrent execution of CPUs and devices
competing for memory cycles
8
Key Interfaces
• Application programming interface (API)
• Application binary interface (ABI)
• Instruction set architecture (ISA) –
COMP4300 (e.g., add $d,$s,$t)
9
How do you startup a computer?
• bootstrap program is loaded at power-up
or reboot
– Typically stored in ROM or EPROM, generally
known as firmware
– Initializes all aspects of system
– Loads operating system kernel and starts
execution
10
Common Functions of Interrupts
• Interrupt transfers control to the interrupt
service routine through the interrupt vector
• Interrupt architecture must save the address
of the interrupted instruction
• A trap or exception is a software-generated
interrupt caused either by an error or a user
request
11
Explain the Interrupt Timeline
A single process is doing output
12
Evolution of Operating Systems
What are the reasons for an OS to evolve
over time?
 Stages include:
Time
Sharing
Multiprogrammed Systems
Batch Systems
Simple
Batch
Systems
Serial
Processing
13
Serial Processing
Earliest Computers:
Problems:
• No operating system
• Scheduling:
• programmers interacted
directly with the
computer hardware
• Computers ran from a
console with display
lights, toggle switches,
some form of input
device, and a printer
• Users have access to the
computer in “series”
14
– most installations used a
hardcopy sign-up sheet to
reserve computer time
– time allocations could run
short or long, resulting in
wasted computer time
• Setup time
– Long system setup time: A
considerable amount of time
was spent just on setting up
the program to run
Exercise 3: How to reduce the long
system setup time of a serial processing
system? (Please use one short sentence
to describe your solution.)
15
Simple Batch Systems
• Early computers were very expensive
 important to maximize processor utilization
• Monitor
 user no longer has direct access to processor
 job is submitted to computer operator who
batches them together and places them on an
input device
 program branches back to the monitor when
finished
16
Job Control Language (JCL)
Special type of programming
language used to provide
instructions to the monitor
what compiler to use
what data to use
17
Exercise 4: What are problems with
simple batch systems?
• Under utilized CPU time
• Non-interactivity of users with running
jobs
18
(a) Uniprogramming
Multiprogramming
Program A
Run
Program B
Wait Run
Wait
Run
Wait
Combined
Run Run
A
B
Wait
Run Run
A
B
Wait
Wait
Run
Wait
Time
(b) Multiprogramming with two programs
• There must be enough memory to hold the OS (resident
monitor) and one user program
Program A
Run
Run
Wait
• When one
job needsWait
to wait for I/O,
the processor
can
switch to the other job, which is likely not waiting for I/O
19
Program
B
Wait Run
Wait
Run
Wait
Time-Sharing Systems
• To handle multiple interactive jobs
• Processor time is shared among multiple users
• Multiple users simultaneously access the system
through terminals, with the OS interleaving the
execution of each user program in a short burst
or quantum of computation
20
Exercise 5: If there are n users actively requesting
service at one time, each user will only see on the
average 1/ n of the effective computer capacity,
not counting OS overhead.
Why the response time on a time-sharing system
can be similar to that on a dedicated computer?
• Relatively slow human reaction time
21
Review
• Basic organization of computer systems
• Goals of operating systems
• Evolution of Operating Systems
– Batching
– Multiprogramming
– Multiprogramming
22