distributed processing terminal-host systems file server program access client server processing

Distributed Processing

Terminal-Host Systems

File Server Program Access

Client Server Processing

2Terminal-Host Systems

Created in the 1960s– Central host computer does all the processing– Terminal is dumb--only a remote screen and keyboard– Created in the 1960s, when microprocessors for

terminal intelligence did not exist

Terminals Host


Sizes

– Mainframes are the largest business hosts Optimized for business uses--file access speed is

more crucial than mathematical processing


Many Mainframe Applications Were Created in the 1960s through 1980s– Legacy systems--systems created by your predecessors

– Would not use the same platform today if built new

– But too expensive to rewrite all legacy applications at once

– Must live with many host legacy applications for now

– Older networks can be legacy systems as well; “legacy system” is not just limited to mainframe applications

5PC Networks

The Most Common Platform in Organizations– Allows PCs to share resources– Both Wintel (Windows/Intel) PCs and Macintoshes

Network

6PC Network Components

File Servers– Store files (data files and programs)– The most common type of server in PC networks– Almost all file servers are themselves PCs

File Server

7File Server Program Access

File Server Program Access is the Most Common Way to Execute Programs in PC Networks– Program files are stored on the file server before

execution

File ServerClient PC

Storedon the

FileServer


File Server Program Access– Program and data files are downloaded (copied) to the

Client PC– Executed on the client PC, not on the file server– File server merely stores programs and data files


Downloaded toClient PC,Executed There


PC Processing Power Limits FSPA Programs– Client PCs do not get very large– Only programs small enough to operate on limited

client PCs can be used


Executed on theClient PC

10Client/Server Processing

Client and Server Machines– Neither has to be a PC– Platform independent

Client Machine Server

11C/S Servers often are Workstation Servers

Workstations– Are computers more powerful (and expensive)

than PCs

– Do not use standard Intel PC microprocessors

– Usually run the UNIX operating system

– Client and server workstations

– Confusingly, Windows NT client operating system is called Windows NT Workstation, where workstation is synonymous with “client”


Two Programs– Client program on client machine– Server program on server machine– Work together to do the required processing


Client ProgramServer

Program


Division of Labor– Client program handles lighter work, such as user

interface chores and light processing chores

– Server program handles heavy work, such as database retrieval



Program


Cooperation Through Message Exchange– Client program sends Request message, such as a

database retrieval request

– Server program sends a Response message to deliver the requested information or an explanation for failure



Program

Request

Response


Widely Used on the Internet

For instance, webservice– Client program (browser) sends an HTTP request

asking for a webserver file

– Server program (webserver application program) sends an HTTP response message with the requested webpage

HTTP Request Message

HTTP Response Message


On the Internet, a Single Client Program--the Browser (also known as the client suite)--Works with Many Kinds of C/S server applications– WWW, some E-mail, etc.

Browser

Webserver

E-mailServer

17Program Functionality (Size)

High program functionality requires large program size

File Server Program Access– Poor: client PCs are small, can only execute small

programs

Client/Server Processing– Good: not limited to client PC processing power– Heavy work can be done on the server machine

Terminal-Host Systems– Good: Hosts can be very large

18Platform Independence

File Server Program Access– Poor: Only works with PC clients and PC file servers– OK for word processing, etc.– Unacceptable for large databases

Client/Server Processing– Excellent: use any server you want, also any client

Terminal-Host Systems– Poor: Hosts require terminals and only work with a few

terminal types

19Scalability

Ability to grow as demand grows

File Server Program Access– Poor: client PCs do not get very large

Client/Server Processing– Very good: Platform independence allows servers to be

larger than PCs– To grow, leave client machine the same, increase the

size of the server machine

Terminal-Host Systems– Excellent: have an enormous range of processing power

20User Interface

File Server Program Access– Very good: uses local PC processing power

Client/Server Processing– Very good: uses local PC processing power for user

interface

Terminal-Host System– Poor: Relies on distant hosts; user interface quality

limited by high long-distance transmission costs– Monochrome, text-only screen; no animation

21Response Time (When User Hits a Key)

File Server Program Access– Very good: uses local PC processing power

Client/Server Processing– Very good: local PC processing power for user interface– But retrievals from the server can cause delays

Terminal-Host System– Poor: Relies on distant hosts; long delays if overloaded

distributed processing terminal-host systems file server program access client server processing

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