HP 9100A, 9100B Programmable Calculators
UvA Computer Museum catalogue nrs 07.14, 01.43
The HP9100A (1968, US$ 4900) is a programmable scientific desk calculator
operating on both fixed-point and floating point decimal data. The
internal representation is floating point BCD (binary coded
decimal), with a twelve digit mantissa and a two digit exponent.
Like the later HP handhelds, the machine uses RPN (reverse Polish
notation). Many mathematical functions are directly available from
the keyboard. The small CRT display shows the stack of three
registers. Two 196-steps programs can be stored on a magnetic card,
using the built-in reader/recorder.
The 9100 uses three types of memory. Built-in subroutines,
constants, and CRT characters are stored in 512 64-bit words of
ROM, consisting of an orthogonal pattern of drive and sense lines
contained in a 16 layer printed-circuit board. Drive pulses are or
are not inductively coupled to the sense lines depending on the
geometry of the pattern at the position of a 0 or 1 valued bit. The
bit density is 1000 bits per square inch.
The control logic uses 64 29-bit words of core ROM. Depending on
whether a word line (one out of 64) is threading or passing one of
the 29 cores (in fact small transformers), a pulse is generated or
not in the core's output winding when the clock source sends a
current pulse over the word line.
Finally, there are 2208 bits of 'standard' coincident-current core
memory (arranged as 6*16*23) implementing the machine's RAM.
In our collection we also have an HP9100B (1969), which has twice the
amount of RAM of the original HP9100A, described above. Furthermore
we have the 9150A monitor scope: a large (and heavy) 19" analog
monitor showing the register stack on a scale suitable for lecture
room demonstrations. The 9160 optical card reader too was mainly
intended for classroom use, mark-sense cards being a cheap
replacement for magnetic cards.
The HP9100A calculator was donated by Walter Frankvoort. The HP9100B, together with peripherals, software and
documentation was donated by Mr. L. van Stratum, Eindhoven, The
Many details about the HP9100A can be found in Bell and Newell
(eds): 'Computer Structures: Readings and Examples', MacGraw-Hill