1.CSE 380Introduction to Operating Systems Insup Lee Fall 00

2. What is an Operating System?

A piece of software that provides a convenient, efficient environment for the execution of user programs.

Hardware Operating systems Systems software Applications software Users 3. Resource Abstraction and Sharing

Hides the details of how the hardware operates

Provides an abstract model of the operation of hardware components

• generalize hardware behavior

• limit the flexibility in which hardware can be manipulated

Computation model: processes, threads

Resources: memory, disk, files, cpu, etc.

4. Why do we need an operating system?

User viewpoint -- provide user interface, command interpreter, directory structure, utility programs (compilers, editors, filters)

Program environment viewpoint -- enhance the bare machine higher-level I/O, structure files, notion of independent processes, improved store (size, protection)

Efficiency viewpoint -- replace a human operator scheduling jobs, storing I/O (files), invoking necessary programs such as compiler

Economic viewpoint -- allow concurrent uses and good scheduling of resources

So, the goals are to make the system convenient to use (via system calls) and to manage resources efficiently.

5. Evolution of an OS

Hardware upgrades

New types of hardware

New services

Fixes

6. Brief History of Operating Systems

1940's -- First Computers

1950's -- Batch Processing

1960's -- Multiprogramming (timesharing)

1970's -- Minicomputers & Microprocessors

Late 1970's, 1980's -- Networking, Distributed Systems, Parallel Systems

1990's and Beyond -- PCs, WWW, Mobile Systems

7. 1940's -- First Computers

Computer dedicated to one user/programmer at a time. Program loaded manuallyby programmer, using console switches. Debugging using console lights.

Advantages:

• Interactive (user gets immediate response)

Disadvantages:

• Expensive machine idle most of time, because people are slow.

• Programming & debugging are tedious.

• Each program must include code to operate peripherals -- error prone, device dependencies.

Libraries of subroutines to drive peripherals are example of typical OS service.

8. 1950's -- Batch Processing

User/programmer submits a deck of cards that describes a job to be executed.

Jobs submitted by various users are sequenced automatically by a residentmonitor.

Tape drives available for batching of input and spooling of output.

Advantages:

• Computer system is kept busier.

Disadvantages:

• No longer interactive; longer turnaround time.

• CPU is still idle for I/O-bound jobs.

OS issues -- command processor (JCL), protection of resident monitor from user programs, loading of user programs after monitor.

9. 1960's -- Multiprogramming (timesharing)

The advent of the I/O processor made simultaneous I/O and CPU processingpossible.

CPU is multiplexed (shared) among a number of jobs -- while one job waitingfor I/O, another can use CPU.

Advantages:

• Interactiveness is restored.

• CPU is kept busy.

Disadvantages:

• Hardware and O.S. required become significantly more complex.

Timesharing - switch CPU among jobs for pre-defined time interval

Most O.S. issues arise from trying to support multiprogramming -- CPU scheduling, deadlock, protection, memory management, virtual memory, etc.

CTSS (Compatible Time Sharing System), Multics

10. 1970's - Minicomputers & Microprocessors

Trend toward many small to mid-range personal computers, rather than a single mainframe.

Early minicomputers and microprocessors were small, so there was some regression to earlier OS ideas.

• e.g. DOS on PC is still essentially a batch system similar to those used in 1960, with some modern OS ideas thrown in (e.g., hierarchical file system).

This trend is changing rapidly because of powerful new microprocessors.

Also, the user interface became more important.

UNIX, DOS

11. Late 1970's, 1980's - Networking

Powerful workstations (e.g., PDP, VAX, Sunstations, etc.)

Local area networks (e.g., Ethernet, Token ring) and long-distance network (Arpanet)

Networks organized with clients and servers

Decentralization of computing requires more communication (e.g., resource sharing)

O.S. issues -- network communication protocols, data encryption, security, reliability, consistency of distributed data

Real-Time Systems timing constraints, deadlines, QoS (90s term)

12. 1990's and Beyond

Parallel Computing (tera-flops)

Powerful PCs, Multimedia computers

High-speed, long-distance communication links to send large amounts of data, including graphical, audio and video

World Wide Web

Electronic notebooks using wireless communication technologies

O.S. issues -- Large heterogeneous systems,mobile computing, etc.

13. Basic OS Concepts

Processes: programs in execution

Resources (e.g., files, memory, display)

• A process must request it from the OS

• The process is blocked until it is allocated

System calls

Shell -- command interpreter

14. Services provided by OS

Program creation

Program execution

Access to I/O devices

Controlled access to files

Error detection and response

• hardware errors (e.g., memory error, device failures)

• software errors (e.g., overflow, out of memory boundary)

Accounting

• collect usage statistics, monitor performance

15. Services Provided by OS (2)

CPU scheduling:allocate computing time among several processes

Memory management:allocate main memory among several processes

Swapping:move processes and their data between main memory and secondary storage

I/O device drivers:specialized code required to operate I/O devices

File system:organize mass storage (disk) into files and directories

Utilities:date/time, accounting, file copy, etc.

Command interpreter:allow users to enter commands interactively

System calls:allow user programs access to O.S. services

Protection:keep processes from interfering with each other and system

Communication & Resource sharing:allow users/processes to communicate (over networks) and share resources(e.g., laser printers, disks, etc.)

Security:protect machines from intruders, worms and viruses

16. Factors in OS Design

Engineering factors:

• Performance/Efficiency -- CPU utilization, resource utilization (e.g. disks), response time

• Correctness/Reliability -- error-free (no software crashes)

• Maintainability -- modular construction, clearly defined interfaces, well-documented

• Small in size-- main memory and secondary storage valuable, larger means more error-prone, larger means takes longer to write

Non-engineering factors:

• Commercial factors

• Standards and open systems

17. Operating System Structure

Monolithic Systems

Layered Systems

Virtual Machines

Client-Server Model