In 1990’s, a distributed processing system having the functions of networking with other computer systems has been a technical trend, particularly in GIS. This is often called "Client Server Architecture" or "Computing Network". Networks can be linked with LAN (Local Area Network) using optical fiber or coaxial cables, WAN (Wide Area Netrwork) or Internet.
Users can select an optimal combination of computers such as personal computers and UNIX workstations which can be connected to each other even at different locations.
There should be a rather powerful computer (usually UNIX workstation) as so called "client server" with big memory and disk capacity, that can be shared with many other computers connected in the network. LAN can be also connected with input and output machines as well as with public telephone lines, mobile telephones, microwave and private telephone lines.
Although personal computers (PCs) had a lot of limitation in memory capacity, processing speed and functions , PCs have become powerful with 32 - bit microprocessor, bigger memory size (64 MB) and bigger hard disk (1 GB) available at very reasonable costs (about 2,000 US dollars depending on the configuration). PCs are useful to control printers, digitizers and color plotters.
UNIX workstations with the function of multi-processing are of course more powerful than PCs in memory size, processing speed and other functions.
A UNIX workstation as a client server can be connected with PCs or X terminals as a controller of input and output devices in GIS.
Figure 5.1 shows a typical GIS computer system.