Dumb and Dumber Computing
The best way to understand what client/server computing is all about is to look at the extremes of what can be called dumb computing – computer applications in which either the client or the server plays dumb, unable to do any share of the work. Dumb computing was the norm for most mainframe/PC computing systems before client/server computing was developed.
In an old-fashioned mainframe computer system, the client is a "dumb" terminal that has minimal processing power, and the server is the mainframe computer itself. As Figure 1-1 illustrates, the server computer does nearly all the work in this type of arrangement. That's why mainframe computers are so grumpy.
This type of computer processing is sometimes called host processing because the host computer – that is, the mainframe – does all the processing work. The client – that is, the terminal – is just along for the ride.
Keep the following points about host processing in mind:
More than one client terminal can access a single host computer. For host processing to work satisfactorily, the host computer itself must be powerful enough to service as many client terminals as the application calls for. In a nationwide airline reservation system, that might mean tens of thousands of client terminals. That's why mainframe computers are so powerful and expensive. The dumb terminal doesn't have to be an old-fashioned mainframe computer terminal.
It may well be a high-powered PC that's pretending to be a dumb terminal. This setup has become very common as companies have replaced old IBM 3270-type terminals with PCs. Workers can use their PCs for PC chores such as word processing and spreadsheets, or they can flip the PC into dumb terminal mode to access their mainframe applications. Once flipped into dumb terminal mode, the PC takes a nap while the host computer does all the work.
The alternative to a dumb terminal is a dumb server, which is how most applications that run on local area networks are set up. The entire work of the application is performed on a client computer – a PC – at the user's desk. The server computer is called upon whenever a file is needed or something needs to be printed, but the server doesn't do any real work. Figure 1-2 shows the balance of power in this type of arrangement.
A dumb server can have one or both of two functions. It can be
- A file server, which means that its disk drive houses all the files used by the application
- A print server, which means that it has a printer attached to it
In a small network, the same computer may be both the file server and the print server. In a larger network, the file and print servers are likely to be separate computers.
Dumb server systems quickly become inefficient as more users are added to the system. To see why, suppose five users access a large customer database file that lives on a file server. If one of the users decides to display a list of all customers whose year-to-date sales exceed $1,000, the entire customer file must be sent over the network from the server computer to the user's client computer. That can tie up the network, slowing down the other four users.
However, the situation is probably tolerable. But suppose the system has 500 users instead of 5, and 100 of the users want the list of customers whose sales exceed $1,000. Now the entire file must be sent over the network simultaneously to 100 different client computers. The entire network will slow to a crawl.
The solution to this problem is client/server computing.
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