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CS212: OPERATING SYSTEM
Lecture 1: Introduction
Chapter 1: Introduction
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
What Operating Systems Do

Computer-System Organization

Computer-System Architecture

Operating-System Structure

Operating-System Operations

Distributed Systems

Computing Environments
Objectives
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
To provide a grand tour of the major operating systems components

To provide coverage of basic computer system organization
What is an Operating System?
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

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
Computer System Structure
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
Computer system can be divided into four components

Hardware – provides basic computing resources
 CPU, memory, I/O devices

Operating system
 Controls and coordinates use of hardware among various
applications and users

Application programs – define the ways in which the system resources
are used to solve the computing problems of the users
 Word processors, compilers, web browsers, database systems, video
games

Users
 People, machines, other computers
Four Components of a Computer System
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The operating system’s Role
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
User View:

Single User (personal computer)
 OS designed for ease of use , with some attention paid to performance.

Multiple User’s (mainframe or minicomputer)
 OS designed to maximize resource utilization.

Workstations users connected to networks of other workstations and servers
 OS designed to compromise between individual usability and resource
utilization.
The operating system’s Role (cont.)
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
System View:


OS is a resource allocator
 Manages all resources
 Decides between conflicting requests for efficient and fair resource
use
 It is important when many users access the same mainframe or
minicomputer
OS is a control program
 Controls execution of programs to prevent errors and improper use
of the computer
 It is especially concerned with the operation and control of I/O
devices.
Operating System Definition
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

No universally accepted definition
“The one program running at all times on the computer” is the kernel. Everything
else is either a system program (ships with the operating system) or an application
program.
An operating system is a software that manages
the computer hardware, as well as providing an
environment for application programs to run.
Computer-System Organization
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


Computer-System Operation
Storage Structure
I/O Structure
Computer System operation
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
Computer-system operation

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
Computer System Operation (cont.)
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Computer Startup:

bootstrap program is loaded at power-up or reboot

Typically stored in ROM or EEPROM, generally known as firmware

Initializes all aspects of system

Loads operating system kernel and starts execution
Computer System Operation (cont.)
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Interrupt:

The occurrence of an event is usually signaled by an interrupt from either
the hardware or the software.

Hardware interrupts by sending a signal to the CPU through system bus.

Software interrupts by executing a special operation called a system call.
The interrupt is signal that gets the attention of the CPU and is usually
generated when I/O is required.
For example,
hardware interrupts are generated when a key is pressed or when the
mouse is moved.
Software interrupts are generated by a program requiring disk input or
output.
Storage Hierarchy
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

Storage systems organized in hierarchy

Speed

Cost

Volatility
Caching – copying information into faster storage system; main memory can be
viewed as a last cache for secondary storage
Storage-Device Hierarchy
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I/O Structure
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


each device controller is in charge of a specific type of device.
A device controller maintains some local buffer storage and a set of
special-purpose registers.
OS have a device driver for each device controller. This device driver
understands the device controller and presents a uniform interface to
device to the rest of the operating system.
Computer-System Architecture
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
Multiprocessors systems growing in use and importance

Also known as parallel systems, tightly-coupled systems

Advantages include
1. Increased throughput
2. Economy of scale
3. Increased reliability – fault tolerance

Two types
1. Asymmetric Multiprocessing (master-slave relationship)
2. Symmetric Multiprocessing (all processors are peers)
Symmetric Multiprocessing Architecture
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A Dual-Core Design
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• Processors were originally developed with only one core.
• The core is the part of the processor that actually performs the reading
and executing of the instruction. Single-core processors can only
process one instruction at a time
• Dual-core processor contains two cores (Such as Intel Core Duo).
Operating System Structure
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
Multiprogramming needed for efficiency




Multiprogramming organizes jobs (code and data) so CPU always has
one to execute. (Increase CPU Utilization.)
A subset of total jobs in system is kept in memory
One job selected and run via job scheduling
When it has to wait (for I/O for example), OS switches to another job
Multiprogramming systems provide an environment in
which the various system resources are utilized effectively,
Not for user interaction with the computer system
Memory Layout for Multiprogrammed System
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Uniprogramming

Processor must wait for I/O instruction to
complete before preceding
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Multiprogramming

When one job needs to wait for I/O, the
processor can switch to the other job
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Multiprogramming
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Utilization Histograms
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Example
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Operating System Structure (cont.)
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
Timesharing (multitasking) is logical extension of multiprogramming in
which CPU switches jobs so frequently that users can interact with each job
while it is running, creating interactive computing
 Response time should be < 1 second
 Each user has at least one program executing in memory process
 If several jobs ready to run at the same time  CPU scheduling
 If processes don’t fit in memory, swapping moves them in and out to run
 Virtual memory allows execution of processes not completely in memory
Time Sharing



Using multiprogramming to handle multiple
interactive jobs
Processor’s time is shared among multiple users
Multiple users simultaneously access the system
through terminals
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Operating-System Operations
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
Dual-mode operation allows OS to protect itself and other system components
 User mode and kernel mode
 Mode bit provided by hardware
 Provides ability to distinguish when system is running user code or kernel code
 Some instructions designated as privileged, only executable in kernel mode
 System call changes mode to kernel, return from call resets it to user
Transition from User to Kernel Mode
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Distributed Systems
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


Distributed systems allow users to share resources on geographically dispersed
hosts connected via a computer network.
The basic types of networks are:

Local-area Network (LAN) connects computers within a room, a floor, or a
building.

Wide-area Network (WAN) links building, cities or countries.
A network operating system

provides features such as file sharing across the network

and includes a communication scheme that allows different processes on
different computers to exchange messages
Computing Environments
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
Traditional computing (Centralized computing)

Office environment
 PCs connected to a network, terminals attached to mainframe or
minicomputers providing batch and timesharing
 Now portals allowing networked and remote systems access to same
resources

Home networks
 Used to be single system, then modems
 Now firewalled, networked
Centralized computing is computing done at a central
location, using terminals that are attached to a central
computer.
Computing Environments (Cont)
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 Client-Server Computing

Many systems now servers, responding to requests generated
by clients
 Compute-server provides an interface to client to request
services (i.e. database)
 File-server provides interface for clients to store and
retrieve files
Peer-to-Peer Computing
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
Another model of distributed system

P2P does not distinguish clients and servers

Instead all nodes are considered peers

May each act as client, server or both

To participate in a P2P system, a node must join P2P network by:
 Registers its service with centralized lookup service on network,
or
 Broadcast request for service and respond to requests for service via
discovery protocol
End of Chapter 1
Operating System Concepts – 8th Edition,
Silberschatz, Galvin and Gagne ©2009