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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
3Terminal-Host Systems
Sizes
– Mainframes are the largest business hosts Optimized for business uses--file access speed is
more crucial than mathematical processing
4Terminal-Host Systems
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
8File Server Program Access
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
File ServerClient PC
Downloaded toClient PC,Executed There
9File Server Program Access
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
File ServerClient PC
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”
12Client/Server Processing
Two Programs– Client program on client machine– Server program on server machine– Work together to do the required processing
Client Machine Server
Client ProgramServer
Program
13Client/Server Processing
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
Client Machine Server
Client ProgramServer
Program
14Client/Server Processing
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
Client Machine Server
Client ProgramServer
Program
Request
Response
15Client/Server Processing
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
16Client/Server Processing
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