Several types of small computers have appeared on the market during the past year, some having 8-bit words, but they are too small for general data-acquisition use, although valuables for special applications. For present purposes, the smallest useful machines have a minimum memory size of 4096 (4k) 12-bit words, which can usually be enlarged to 32k words by the addition of memory modules, while the larger machines have minimum memories of at least 8k, with provision for expansion to several hundred k. Regardless of their size, the machines of the present generation all have memory cycle times around 1 or 2 µsec.
2. Rough Classification of Computers
Before proceeding with the discussion it is convenient to find a simple scheme for classifying computers. The scheme adopted here is to divide them into three loosely defined classes—small, medium, and large—essentially on the basis of the properties of the basic central processors:
Small
Word length 12 to 18 bits
Useful memory size 4k
Number of bits in instruction 3 or 4
Floating-point hardware orally offered
Approximate cost range $8500 to $40,000
Medium
Word length 16 to 24 bits
Useful memory size 8 to 16k
Number of bits in instruction 4 to 6
Floating-point hardware option sometimes offered
Approximate cost range $30,000 to $120,000
Large
Word length 32 to 48 bits
Useful memory size at least 16k
Number of bits in instruction 7 or more
Floating-point hardware
Approximate cost range $150,000 or more
Computers do not fall neatly into these three classifications, especially since manufacturers offer many optional features; therefore, some argument about the assignment of a particular machine to one or the other class is possible. This is especially true with respect to the small and medium types. The properties of a large number of small and medium-sized computers are given in Appendix A. Information on larger machines can be found in the Adams Associates Computer Characteristics Quarterly.
D. MATCHING COMPUTERS TO TASKS
Having classified both the computers and the jobs that they may be called on to do, we now ask this question: How suitable is each of the three types of computers for each of the three classes of jobs, given that in every case the acquisition system consists of a single computer coupled to all necessary input and output equipment?