1.4 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

Requires networking infrastructure.

Local area networks (LAN) or Wide area networks (WAN) May be either client- server or peer- to- peer systems.

General Structure of Client- Server 

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.

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.

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.

Handheld Systems

Personal Digital Assistants (PDAs)  Cellular telephones Issues:

Limited memory

Slow processors

Small display screens.

Migration of Operating- System Concepts and Features

Computing Environments

Traditional computing

Web- Based Computing

Embedded Computing