1. Quick Introduction to OS
DEPARTMENT OF COMPUTER SCIENCE AND SOFTWARE ENGINEERING
CONCORDIA UNIVERSITY
Quick Introduction to OS
by-Istiaque Shahriar
Quick Introduction to OS
January 17, 2007

2. Quick Introduction to OS
Outline
Computers and Software
General System Software
Resource Abstraction
Resource Sharing
System Software and OS
OS Evaluation
Batch Systems
Timesharing Systems
Real Time OS
Distributed OS
Web OS
Modern OS Genesis
Basic OS Organization
Quick Introduction to OS

3. Computers and Software
Two major groups of software:
Application software: Designed to solve a specific problem (eg. MS Word)
System software: provides a general programming environment.
For application software it provides
The functions to be used
The mechanisms to share the hardware in an orderly fashion.
Sharing
Increases overall performance (by allowing different application software to use different parts or resources of the computer at the same time).
Decreases the time for execution of a collection of programs
Operating system is a subset of the system software.
Quick Introduction to OS

4. System Software: General Applications
Runtime system for a programming language (API)
Usually implemented in C libraries (Unix, Windows):
Standard input/output (I/O) library – procedures to perform buffered input/output on a stream of data;
The math library – functions to perform various mathematical computations;
Graphics libraries – functions to render images on a bitmapped display
Window system – software that provides a virtual terminal to an application program.
Database Management System (DBMS) – stores and manipulate information (data) on storage devices (e.g. disks) and retrieved at the time of need.
Operating system – interacts directly with the hardware to provide an interface to other system software and with application software whenever it wants to use system’s (computer’s) resources. An OS
is application domain independent;
provides resource abstraction and management;
provides resource sharing (through strict resource management policies).
Provides convenient environment for the Users
Quick Introduction to OS

5. Operating System Aspects
Key aspects of the OS:
Resource Abstraction
Resource Sharing
What is Resource?
The OS treats any entity as a resource if it satisfies following characteristics:
A process must request that entity from the OS.
A process must suspend its operation until the entity is allocated to it.
Anything like CPU cycle, Main memory, printer…..
Quick Introduction to OS

6. Resource Abstraction Aspects
Similar resources can be abstracted to a common abstract resource interface (i.e. system software may abstract floppy disks, hard-disks and CD-ROMs into a single abstract disk interface).
Abstraction generalizes the hardware behavior but restricts the flexibility.
With abstraction, certain operations become easier to perform, other may become impossible (such as specific hardware control).
Different hardware components that a program may use are referred to as resources. Any particular resource, such as a HDD has a generic interface that defines how the programmer can make the resource perform a desired operation.
An abstraction can be made to be much simpler than the actual resource interface.
Quick Introduction to OS

7. Resource Sharing Aspects
Abstract and physical resources may be shared among a set of concurrently executing programs.
Two kinds of resource sharing:
Space multiplexed sharing
Resource can be divided in two or more distinct units, which units units can be used independently.
Different executing programs, or processes can allocate exclusive control of different units of a resource at the same time e.g. Main memory and HDD.
Time multiplexed sharing
The resource is not spatially divisible.
A process is allocated exclusive control of the entire resource for a short period of time.
After specified time has elapsed, the resource is de-allocated from the process and allocated to another.
Quick Introduction to OS

8. Abstract View of System Components
Quick Introduction to OS

9. Quick Introduction to OS
System Software and OS
Quick Introduction to OS

10. Operating Systems Evolution
Computers with no operating system (Only Operators)
Programming in machine language.
Lack of I/O devices.
OS rudiments
Programming done in assembly.
Some basic I/O devices (may be punch card readers).
Some I/O control modules, assembler, debugger, loader, linker (limited).
Batch processing systems – serve a collection of jobs, called a batch, from a queue:
Job – predefined sequence of commands, programs and data combined into a single unit.
The user doesn’t interact with programs while they operate.
Batch – preferably of similar type of jobs
Quick Introduction to OS

11. Operating Systems Evolution
Multiprogramming OS–
the technique of loading multiple programs into space multiplexed memory while time-multiplexing the processor.
Timesharing systems.
Real time operating systems.
Distributed operating systems.
Multiprogramming systems common features
Multitasking – multiple processes sharing machine resources.
Hardware support -for memory protection and I/O devices.
Multi-user and multi-access support (through time sharing mechanisms).
Interactive user interface.
Quick Introduction to OS

12. Batch Systems’ Aspects
Processor scheduling: FIFO.
Memory management:
Memory is divided in two parts:
system memory and
program memory (for programs).
I/O management – no special problems, since a job has exclusive access to the I/O devices.
File management – a critical issue in multiprogramming batch systems.
Quick Introduction to OS

13. Timesharing Systems’ Aspects
Support for multiprogramming and multi-user.
Processor scheduling
Time slicing.
Memory management
Protection and inter-process communication support.
I/O management
Support for protection and sharing between users.
File management
Protection support and sharing support between users.
Quick Introduction to OS

14. Real Time Operating Systems’ Aspects
Used whenever a large number of external events have to be treated in a short or limited interval of time.
Main goal
Minimization of the response time to serve the external events.
Processor scheduling:
Priority based preemptive. Why??
Memory management:
Concurrent processes are loaded into memory.
Support for protection and inter-process communication.
I/O management
Critical in time.
Processes dealing with I/O are directly connected to the interrupt vectors.
Soft Real time system
Hard Real time system
Quick Introduction to OS

15. Distributed Operating Systems’ Aspects
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
App
Distributed OS
Multiple computers connected via a network
Quick Introduction to OS

16. Web Operating Systems’ Aspects
WebOS is a university project at University of California, Berkeley. WebOS provides basic operating system services needed to build applications that are:
geographically distributed;
highly available;
incrementally scalable;
dynamically reconfiguring.
WebNFS – bringing the file system to the Internet. Features:
Is based on TCP/IP.
Works through firewalls.
Read-ahead for faster data access.
Write-behind for faster data writes over internet.
Print sharing and queue management.
Centralized server administration.
Quick Introduction to OS

17. Basic Operating System Organization
Basic functions - device management, process and resource management, memory management, file management
Operating System
Process and
Resource Manager
File
Manager
Memory
Device
Computer Hardware
Processor (s)
Main Memory
Devices
Quick Introduction to OS

18. Quick Introduction to OS
References
Garry Nutt, “Operating Systems – A Modern Perspective”, Second Edition, Wesley, 2002
WebNFS, Technical Overview, Sun Microsystems,
WebOS: Operating System Services for Wide Area Applications,
Quick Introduction to OS