Csc4320 Chapter 1

Chapter 1
Introduction to Operating System
Bernard Chen
Spring 2007
Outline
1.1 What is OS
1.2 Computer System Organization
1.3 Computer System Architecture
1.4 OS Structure
1.5 OS Operations
1.6-1.8 Process, Memory, Storage management
1.9 Protection and Security
1.10~ Systems
1.1 What is Operating System?
 An operating system is a program that
manages the computer hardware.
 It also provides a basis for application

programs and acts as an intermediary
between the computer user and
computer hardware.
What do Operating System do?
 The computer system can be divided
roughly into four components:
1. The hardware
2. The operating system
3. The application software
4. The Users
USER View of OS
 Ease to use (Home PCs)
 Efficient resource utilization

(Work stations)
SYSTEM view of OS
 OS is a resource allocator
Manages all resources (CPU time, memory
space, storage space, I/O and so on)
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
1.2 Computer System
Organization
 Basic Organization
 Storage Structure
 I/O structure
Computer Startup
Bootstrap program is loaded at power
up or reboot
 Typically stored in ROM, generally
known as firmware
 Initialize all aspects of system
 Loads operating system kernel and
starts execution
1.2.1 Computer System
Organization
1.2.1 Computer System
Organization
 I/O devices and the CPU can execute
concurrently.
 Each device controller is in charge of a
particular device type.
 Each device controller has a local
buffer.
Interrupt Timeline
1.2.2 Storage Structure
Main Memory:
 Main memory is the only large storage
media that the CPU can access directly

 Main memory is usually too small to
store all needed programs and data

 Main memory is a volatile storage
device that loses its contents when

power is off
 Therefore, most computer provide
secondary storage as extension to
store web browser, compliers, word
processors…etc
Storage Device Hierarchy
 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.
Performance of Various
Levels of Storage
Caching
 Information in use copied from slower

to faster storage temporarily
 Important principle, performed at many
levels in a computer (in hardware,
operating system, software)
Caching
 Faster storage (cache) checked first to
determine if information is there
If it is, information used directly from the cache (fast)
If not, data copied to cache and used there
 Cache is usually smaller than storage being

cached
 Cache management is an important design
problem
 Cache size and replacement policy
1.3 Computer-System
Architecture
 1.3.1 Single-Processor Systems
 1.3.2 Multiprocessor Systems
 1.3.3 Cluster Systems
1.3.1 Single-Processor Systems
 On a single processor system, there is only
one main CPU capable of executing a general
purpose instruction set.
 Some other special-purpose processors may

also included. Such as:
GPU
Disk-controller microprocessor
Keyboard microprocessor
1.3.2 Multiprocessor Systems
 Also called Parallel Systems
 Advantages:
1. Increase throughput
2. Economy of scale
3. Increase reliability (fault tolerant)
1.3.2 Multiprocessor Systems
 Two types of multiprocessor systems:
1. Asymmetric multiprocessing
(master and slave processors)
2. Symmetric multiprocessing
(Shared memory system)
1.3.3 Clustered Systems
 Clustered computers share storage and
are closely linked via Local-area
network (LAN) or a faster
interconnection.
1.4 OS Architecture
One of the most important aspect of OS is the
ability to Multiprogramming
 Single user cannot keep CPU and I/O devices

busy at all times
 One job selected and run via job scheduling
 When it has to wait (for I/O for example), OS
switches to another job
Memory Layout for
Multiprogrammed System
Multiprogramming
 Jobs are stored in “Job Pool”
 Virtual memory is the useful
technique for the limitation size of
physical memory
1.5 OS operations
 Interrupt (driven by hardware) vs.
Trap (called by software or error)
 Trap example: divide by 0; invalid memory access
 We need to make sure that an error in a user

program could cause problems only for the
one program that was running (such as infinite
loop)
Dual Mode Operation
 Dual-mode operation allows OS to protect
itself and other system components
 It contains user mode (mode bit:1) and
Kernel mode (mode bit:0)
 The operating system loaded user application starts

in user mode. Whenever a trap or interrupt occurs,
hardware switches to kernel mode.
Transition from user to kernel mode
C library handling of write()
#include<stdio.h>
Int main()
{
…
printf(“hellow world”);
…
}
User mode
Standard C library
Kernel mode
Write()
system call
Dual Mode Operation
 Privileged instructions: some
machine instructions that may cause
harm, can only be executed in kernel
mode.
 Such as instruction switch to user mode; I/O control;

timer management, and interrupt management.
Timer
To prevent the OS out of control by CPU
 Set interrupt after specific period

 Operating system decrements counter
 When counter zero generate an interrupt
 Set up before scheduling process to regain
control or terminate program that exceeds
allotted time
Process management
 A process is a program in execution. It
is a unit of work within the system.
 Process needs resources to accomplish
its task CPU, Memory, files, I/O devices
 Process termination requires reclaim of
any reusable resources
Process management
 Single-threaded process has one
program counter (PC) specifying
location of next instruction to execute
Process executes instructions sequentially, one at a
time until completion
 Multi-threaded process has one

program counter per thread
Process management
The operating system is responsible for the
following activities in connection with process
management:
 Creating and deleting both user and system processes (Ch3)

 Suspending and resuming processes (Ch5)
 Providing mechanisms for process synchronization (Ch6)
 Providing mechanisms for process communication (Ch4)
 Providing mechanisms for deadlock handling(ch7)
Memory Management
 All data in memory before and after

processing
 All instructions in memory in order to execute
 Memory management determines what is in
memory when optimizing CPU utilization and
computer response to users
Memory management
activities
 Keeping track of which parts of memory

are currently being used and by whom
 Deciding which processes and data to
move into and out of memory
 Allocating and deallocating memory
space as needed
Storage Management
OS provides uniform, logical view of
information storage
 file
 Each medium is controlled by device (i.e., disk drive,
tape drive)
Storage Management
File-System management
 Files usually organized into directories
 Access control on most systems to determine who
can access what
 OS activities include
1. Creating and deleting files and directories
2. Primitives to manipulate files and dirs
3. Mapping files onto secondary storage
4. Backup files onto stable (non-volatile) storage media
Mass Mass-Storage
Management
 Usually disks used to store data that does not fit in
main memory or data that must be kept for a “long”
period of time.
 OS activities
1. Free-space management
2. Storage allocation
3. Disk scheduling
4. Tertiary storage includes optical storage, magnetic
tape
5. Varies between WORM (write-once, read-many-
times) and RW (read-write)
Protection and Security
 Protection–any mechanism for controlling

access of processes or users to resources
defined by the OS (Ch14)
 Security–defense of the system against

internal and external attacks even when
protection is activated (Ch15)
(including denial-of-service, worms, viruses, identity
theft, theft of service)
Protection and Security
Systems generally first distinguish among users, to
determine who can do what
 User identities (user IDs, security IDs) include name

and associated number, one per user
 User ID then associated with all files, processes of
that user to determine access control
 Group identifier (group ID) allows set of users to be
defined and controls managed, then also associated
with each process, file
 Privilege escalation allows user to change to
effective ID with more rights
Computing Environments
Traditional computer
 Used to be single system, then modems

 Now firewalled, networked
Client-Server computing
 Many system now servers, responding
request to clients
Peer Peer-to to-Peer
Computing
 Another model of distributed system
 P2P does not distinguish clients and
servers
1. Instead all nodes are considered peers

2. May each act as client, server or both
3. Node must join P2P network
Web-Based computing
 Web has become ubiquitous

 More devices becoming networked to
allow web access, such as work
stations, PDA, even cell phone
Operating System Services
 User interface
 Program execution
 File-system manipulation
 Communication
 Error detection
 Resource allocation
 Accounting
 Protection and security

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Chapter 1

Introduction to Operating System

 It also provides a basis for application

 Efficient resource utilization

 Loads operating system kernel and

media that the CPU can access directly

store all needed programs and data

device that loses its contents when

 Information in use copied from slower

 Cache is usually smaller than storage being

 Some other special-purpose processors may

 Single user cannot keep CPU and I/O devices

 We need to make sure that an error in a user

 The operating system loaded user application starts

 Such as instruction switch to user mode; I/O control;

 Set interrupt after specific period

 Multi-threaded process has one

 Creating and deleting both user and system processes (Ch3)

 All data in memory before and after

 Keeping track of which parts of memory

 Protection–any mechanism for controlling

 Security–defense of the system against

 User identities (user IDs, security IDs) include name

 Used to be single system, then modems

1. Instead all nodes are considered peers

 Web has become ubiquitous

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