Chapter 1: Introduction

Operating System Concepts

What

is an Operating System?
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.

Operating System Concepts

Computer System Components
1. Hardware – provides basic computing resources
(CPU, memory, I/O devices).
2.Operating system – controls and coordinates the use
of the hardware among the various application
programs for the various users.
3. Applications programs – define the ways in which the
system resources are used to solve the computing
problems of the users (compilers, database systems,
video games, business programs).
4.Users (people, machines, other computers).
Operating System Concepts
Operating System Concepts
Operating System Definitions
Resource allocator – manages and allocates
resources.
Control program – controls the execution of
user programs and operations of I/O devices .
Kernel – the one program running at all
times.

Operating System Concepts

Operating System Concepts
Several jobs are kept in main memory at the same time, and the
CPU is multiplexed among them.

Operating System Concepts

OS Features Needed for Multiprogramming
I/O routine supplied by the system.
Memory management – the system must
allocate the memory to several jobs.
CPU scheduling – the system must choose
among several jobs ready to run.
Allocation of devices.

Operating System Concepts

Time-Sharing Systems–Interactive Computing

The CPU is multiplexed among several jobs that

are kept in memory and on disk (the CPU is
allocated to a job only if the job is in memory).
A job swapped in and out of memory to the disk.
On-line communication between the user and
the system is provided; when the operating
system finishes the execution of one command, it
seeks the next “control statement” from the user’s
keyboard.

Operating System Concepts

Desktop Systems
Personal computers – computer system dedicated
to a single user.
I/O devices – keyboards, mice, display screens,
small printers.
User convenience and responsiveness.
Can adopt technology developed for larger
operating system’ often individuals have sole use
of computer and do not need advanced CPU
utilization of protection features.
May run several different types of operating
systems (Windows, MacOS, UNIX, Linux)

Operating System Concepts

Parallel Systems
Multiprocessor systems with more than on CPU in
close communication.
Tightly coupled system – processors share memory
and a clock; communication usually takes place
through the shared memory.
Advantages of parallel system:
Increased throughput
Economical
Increased reliability
 graceful degradation
 fail-soft systems

Operating System Concepts

Parallel Systems (Cont.)
Symmetric multiprocessing (SMP)
 Each processor runs and identical copy of the
operating system.
 Many processes can run at once without
performance deterioration.
 Most modern operating systems support SMP
Asymmetric multiprocessing
 Each processor is assigned a specific task; master
processor schedules and allocated work to slave
processors.
 More common in extremely large systems

Operating System Concepts

Operating System Concepts
Distributed Systems
Distribute the computation among several
physical processors.
Loosely coupled system – each processor has its
own local memory; processors communicate with
one another through various communications
lines, such as high-speed buses or telephone lines.
Advantages of distributed systems.
 Resources Sharing
 Computation speed up – load sharing
 Reliability
 Communications

Operating System Concepts

Distributed Systems (cont)
Requires networking infrastructure.
Local area networks (LAN) or Wide area
networks (WAN)
May be either client-server or peer-to-peer
systems.

Operating System Concepts

Operating System Concepts
Clustered Systems
Clustering allows two or more systems to share
storage.
Provides high reliability.
Asymmetric clustering: one server runs the
application while other servers standby.
Symmetric clustering: all N hosts are running the
application.

Operating System Concepts

Real-Time Systems
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.
Well-defined fixed-time constraints.
Real-Time systems may be either hard or soft
real-time.

Operating System Concepts

Real-Time Systems (Cont.)
Hard real-time:
 Secondary storage limited or absent, data stored in
short term memory, or read-only memory (ROM)
 Conflicts with time-sharing systems, not supported
by general-purpose operating systems.

Soft real-time
 Limited utility in industrial control of robotics
 Useful in applications (multimedia, virtual reality)
requiring advanced operating-system features.

Operating System Concepts

Handheld Systems
Personal Digital Assistants (PDAs)
Cellular telephones
Issues:
Limited memory
Slow processors
Small display screens.

Operating System Concepts

Computing Environments
Traditional computing
Web-Based Computing
Embedded Computing

Operating System Concepts