SPECIAL-PURPOSE AND GENERAL-PURPOSE COMPUTERS
In general, there are two types of digital computers. The first is the special-purpose digital computer, which performs a fixed and pre-set sequence of calculations. This type of computer may be constructed more efficiently than the general purpose computer. Because of the advantages in construction, special-purpose computers are used where such factors as weight, power consumption, etc. are critical, as in aircraft control systems, missile guidance systems, etc.
The second type of computer is defined as a general purpose digital computer. The sequence of instructions which the machine follows is generally read into this type of machine and stored in the memory of the machine. The machine can be made to follow another sequence of instructions by simply reading in the desired set of instructions. Since the sequence of operations performed by the general-purpose digital computer may be easily changed, the machine possesses greater flexibility, and this is the type of machine generally used in business and scientific applications.