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

2 Terminal-Host Systems n 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 TerminalsHost

3 Terminal-Host Systems n Sizes – Mainframes are the largest business hosts n Optimized for business uses--file access speed is more crucial than mathematical processing

4 Terminal-Host Systems n 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 n The Most Common Platform in Organizations – Allows PCs to share resources – Both Wintel (Windows/Intel) PCs and Macintoshes Network

6 PC Network Components n 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

7 File Server Program Access n 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 Server Client PC Stored on the File Server

8 File Server Program Access n 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 Server Client PC Downloaded to Client PC, Executed There

9 File Server Program Access n 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 Server Client PC Executed on the Client PC

10 Client/Server Processing n Client and Server Machines – Neither has to be a PC – Platform independent Client MachineServer

11 C/S Servers often are Workstation Servers n 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”

12 Client/Server Processing n Two Programs – Client program on client machine – Server program on server machine – Work together to do the required processing Client MachineServer Client Program Server Program

13 Client/Server Processing n 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 MachineServer Client Program Server Program

14 Client/Server Processing n 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 MachineServer Client Program Server Program Request Response

15 Client/Server Processing n Widely Used on the Internet n 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

16 Client/Server Processing n 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 , etc. Browser Webserver Server

17 Program Functionality (Size) n High program functionality requires large program size n File Server Program Access – Poor: client PCs are small, can only execute small programs n Client/Server Processing – Good: not limited to client PC processing power – Heavy work can be done on the server machine n Terminal-Host Systems – Good: Hosts can be very large

18 Platform Independence n File Server Program Access – Poor: Only works with PC clients and PC file servers – OK for word processing, etc. – Unacceptable for large databases n Client/Server Processing – Excellent: use any server you want, also any client n Terminal-Host Systems – Poor: Hosts require terminals and only work with a few terminal types

19 Scalability n Ability to grow as demand grows n File Server Program Access – Poor: client PCs do not get very large n 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 n Terminal-Host Systems – Excellent: have an enormous range of processing power

20 User Interface n File Server Program Access – Very good: uses local PC processing power n Client/Server Processing – Very good: uses local PC processing power for user interface n Terminal-Host System – Poor: Relies on distant hosts; user interface quality limited by high long-distance transmission costs – Monochrome, text-only screen; no animation

21 Response Time (When User Hits a Key) n File Server Program Access – Very good: uses local PC processing power n Client/Server Processing – Very good: local PC processing power for user interface – But retrievals from the server can cause delays n Terminal-Host System – Poor: Relies on distant hosts; long delays if overloaded