236 Part 3 The instruction-set processor level: variations in the processor
Section 4 Desk calculator computers: keyboard processors with small memories
The implementation has approximately 36.2 kb of memory, including the read-only and read-write parts. The design is physically outstanding, and its use of microprogramming is superb. The reader should note there are two levels of M(read only). We could draw the PMS structure of Pc as a P.microprogrammed within a P.microprogrammed. HP rightfully regards the two ISP's (29-bit and 64-bit word) as proprietary and carefully avoids discussing these points in the article (Chap. 20). It might be noted that an IBM System/360 Model 30 requires about 2.9 milliseconds for a floating-point square root, whereas the HP 9100A requires 19 milliseconds. By way of evidence of its outstanding packaging, its cost is about five-eighths that of a PDP-8/l for about the same amount of physical hardware. The cost difference, though truly difficult to compare, is partially the result of a design from an instrument maker (Hewlett-Packard) versus a design from a computer manufacturer (DEC). The TV-like construction of the HP 9100A is an important lesson that computer manufacturers have not learned. In other words, a Henry Ford has yet to emerge from the computer field. (Our guess is that he may come from Japan.)
Whereas many computers in this book are included because they are typical of points in the computer space, the HP 9100A is included because it is innovative. It is worthy of note that only one of the engineers had some computer design experience; Cochran, who did the programming, had prior experience with circuitry and instrumentation. Had he been a programmer by training, a larger Mp might have been required. By way of comparative evidence, the IBM 1800 floating-point arithmetic functions +, -, x, /, sin, cos, tan-1, Ö , log, exponential, tanh, binary to decimal, and decimal to binary require approximately 1,425 16-bit words, or 23 kb. On the other hand, the FOCAL1 interactive calculator program for a 4,096-word PDP-8 (49 kb) provides the user with all but polar-rectangular coordinates and hyperbolic functions, but it does have a complete program editing capability, text handling, control structure, and 1,600-character Mp.
1Similar in scope to Dartmouth's BASIC.