Distributed Processing

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Distributed Processing

• Terminal-Host Systems
• File Server Program Access
• Client Server Processing

2
Terminal-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
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Terminal-Host Systems

• Sizes
• Mainframes are the largest business hosts
• Optimized for business uses--file access speed is
  more crucial than mathematical processing

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Terminal-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

5
PC Networks

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

Network
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PC 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
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File 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

Stored on the File Server
Client PC
File Server
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File 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

Downloaded to Client PC, Executed There
Client PC
File Server
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File 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

Executed on the Client PC
Client PC
File Server
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Client/Server Processing

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

Client Machine
Server
11
C/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

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Client/Server Processing

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

Server Program
Client Program
Client Machine
Server
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Client/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

Server Program
Client Program
Client Machine
Server
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Client/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

Server Program
Client Program
Request
Response
Client Machine
Server
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Client/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
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Client/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.

E-mail Server
Browser
Webserver
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Program 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

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Platform 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

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Scalability

• 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

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User 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

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Response 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