A Computer system is mainly composed of hardware and software.
a. Hardware system
A hardware system is supported by several hardware components.
Central processing unit (CPU)
CPU executes the programs and controls the operation of all components.
Usually a personal computer (PC) or a work station is selected for the required CPU or as a server computer.
Memory
Main memory :essential for the operation of the computer because all data and program must be in main memory for fastest access. More than 64 M bytes are at least necessary for PC based GIS.
Auxiliary memory : is used for large permanent or semi-permanent files with slower access. Harddisks, floppy disks, magnetic tapes, or optical compact disks (CD-ROM) are used. At least more than 1 G bytes is required for hard disk in GIS.
Peripherals
Input devices : key board, mouse, digitizers, image scanners, digital cameras, digital photogrammetric workstations etc.
Output devices : color displays, printers, color plotters, film recorders etc. Figure 1.5 shows an exammples of components of a GIS hardwaare system.
b. Software System
A software system is composed of programs including operating system, compilers and application programs.
Operating System (OS) : controls the operation of the programs as well as all input and output.
For Pcs : MS-DOS (IBM PCs) and WINDOWS is the dominant OS.
For Workstations : UNIX and VMS are the dominant OSs.
Compilers : convert a program written in a computer language to machine code so that CPU can execute binary operation. Commonly used languages include C, Pascal and FORTRAN and BASIC etc.
Application Programs : Many vendors are providing GIS software systems as listed in Table 1.3.