14 COMPUTER ENGINEERING
price/higher performance evolution, operating to move up out of their class.
While movement by computer designs and computer suppliers between and among the various classes may be encouraged by price and performance trends, the speed with which that movement occurs is moderated by the software compatibility considerations discussed earlier. The computer class thesis is not meant to imply that each class implements the same instruction set processor and processor-memory-switch configurations with the only difference being speed. Rather, much specialization occurs in each class, and many of the attributes of the higher performance machines appear in substantially less degree in the lower performance classes. For example, there are more data-types in the larger machines, their address spaces (both physical and virtual) are larger, and the software support is generally broader. Re sources devoted to increasing reliability and availability are more common in the higher priced machines. The PDP-l1 Family, from the LSI-l1 up to the VAX-l1/780, exemplifies these functionality differences.
Definition of the Minicomputer
The concept of computer classes that can be distinguished by price and named submicro, micro, mini, midi, maxi, and super may be of assistance in finding a definition for the minicomputer, a definition which has thus far been rather elusive. While the classes suggest that minicomputers are those computers whose prices fall between microcomputers and midi computers, and thus somewhere near the middle of the range of computers available, earlier definitions [Bell and Newell, 1971a] use the term mini to denote minimal.
The Marketplace View defines new computer classes according to price and established computer classes according to performance. This would suggest that a definition of the mini computer should include some historical data on price and some comments on performance, or at least some indication of performance by a discussion of applications and configurations. In 1977 Gordon Bell provided such a hybrid definition for the Director of Computer Resources, U. S. Air Force. The definition was as follows:
MINICOMPUTER: A computer originating in the early 1960s and predicated on being the lowest (minimum) priced computer built with current technology. From this origin, at prices ranging from 50 to 100 thousand dollars, the computer has evolved both at a price reduction rate of 20 percent per year and has also evolved to have increased functionality and a slightly higher price with increasing functionality and performance.
Minicomputers are integrated into systems requiring direct human and process interaction on a dedicated basis (versus being configured with a structure to solve a wide set of problems on a highly general basis).
Minicomputers are produced and distributed in a variety of ways and levels- of-integration from: printed circuit boards containing the electronics; to boxes which hold the processor, primary memory, and interfaces to other equipment; to complete systems with peripherals oriented to solving a particular application(s) problem. The price range(s) for the above levels-of-integration, in 1978, are roughly: 500 to 2,000; 2,000 to 50,000; and 5,000 to 250,000.
This discussion of the Marketplace View has been a qualitative explanation of the effect of technology on the computer industry. It is an engineering view, rather than one that would be given by technology historians or economists. The 20 years described in this book and the individual cost and performance measures surely invite analysis by professionals. The studies re ported in Phister [1976] and Sharpe [1969] are a good departure point.