John Wolff's Web Museum

Compucorp Calculators

Compucorp Label (6kb) The Computer Design Corporation of Los Angeles was an electronic engineering company that designed and built a range of advanced desktop and portable calculators in the early 1970s. The machines were sold through a number of the established mechanical calculator companies (notably Monroe), and also under their own "Compucorp" brand.

The Compucorp machines used an advanced computer-like architecture in which the functionality of the various models was tailored by firmware rather than hardware. The machines were well designed, well built, and reasonably priced, but unfortunately did not survive the "calculator wars" of the mid-1970s. The company moved into business computer systems for a short time, but disappeared in the early 1980s.


C155 External View (8kb) Compucorp Model 155 "Surveyor", S/N 3555019
Functions: Scientific, programmable, special surveying functions
Programming: Keyboard or external 80-column card reader
Technology: MOS-LSI (AMI, 30 chips)
Display: 21-column impact printer, 8-bit register display
Dimensions: 380W x 405D x 175H, weight 10.9kg
Manufactured: Computer Design Corporation, Los Angeles, January 1972
Original Owners: John B White Pty Ltd, Sydney, Australia

This Model 155 "Surveyor" from 1971-2 is one of Compucorp's first generation of programmable scientific desk calculators. All of the 100-series machines have a common computer-like architecture based on a set of 18 custom-designed MOS-LSI chips. The basic design was then customised for specific industries (science, statistics, surveying, etc) by changing the internal program ROMs and the keyboard layouts. The machines were available with either a numeric (Nixie tube) display or an internal printer, but not both. Programs could be entered from the keyboard, or they could be prepared off-line on standard 80-column punched cards and entered through a separate optical card reader. A similar range of machines customised for commercial applications was sold as the 200 series.

The 100-series machines all provided scientific notation, trig and log funtions, powers and roots, and multiple storage registers with register arithmetic. The specialised functions on this Model 155 "Surveyor" include calculations of bearings, traverses, and rectangular to polar conversions.

The machine illustrated was donated to the museum by John B White Pty Ltd, Consulting Surveyors, of Sydney, Australia. It was purchased new in 1972, and was used regularly for survey computations including closes, areas, adding & subtracting bearings, missing bearings and distances, calculating joins between co-ordinates, calculating curves, and various conversions. To do a property close it took around 8 punch cards! The Compucorp was retired in around 1979 in favour of the new HP-25C programmable pocket calculators.

A more detailed description of the Compucorp 155 is available in the Technical Section.

Compucorp 320G Compucorp Model 320G "Micro Scientist", S/N 4202373
Functions: Scientific, 10 memories
Technology: MOS-LSI by Texas Instruments, MOS memory
Display: 13 significant digits plus 2 exponent, 7-segment Panaplex
Dimensions: 135W x 230D x 75H, weight 1.15kg (without batteries)
Manufactured: Compucorp USA, 1973.

Compucorp's second-generation calculators (the 300 series) were introduced in 1972. The "Micro Scientist" series (models 320 to 326) were among the first to provide scientific functions and programmability in a portable battery-powered machine. The "Statistician" (models 340/342/346) and "Bond Trader" (model 360) provided similar advanced capabilities in different application areas.

The Compucorp 320 is the base model of the "scientific" series. It provides full scientific notation, a broad range of trig and log functions, powers and roots, angle and coordinate conversions, and 10 addressable storage registers with register arithmetic. At a time when many calculators still used fixed decimal points, the Compucorp provided a numeric range of 10-99 to 10+99, with all numbers handled internally to 13 significant figures. Accuracy in the scientific functions is typically 1 part in the 12th figure, and never worse than 1 part in the 11th. Machines with the G suffix can switch between degrees and grads for trigonometric calculations. The basic 320/320G models are not programmable.

The 300-series machines would operate for over 3 hours from four rechargeable D-size NiCad batteries (of 1970s vintage), or 2 hours from carbon-zinc cells. Running times would be considerably longer with modern NiMH or alkaline cells. The external battery charger and mains power supply is rated at 7.5V DC at 1.3A (10W approx).

A more detailed description of the Compucorp 320 series "Micro Scientist" series is available in the Technical Section.

Compucorp 324G Compucorp Model 324G "Micro Scientist", S/N 4201133
Functions: Scientific, programmable, 10 memories
Programming: 2 x 80 steps, all keystrokes, no conditionals
Technology: MOS-LSI by Texas Instruments, MOS memory
Display: 13 significant digits plus 2 exponent, 7-segment Panaplex
Dimensions: 135W x 230D x 75H, weight 1.15kg (without batteries)
Manufactured: Compucorp USA, 1973.

All of the remaining models in the "Scientist" series include a basic programming capability. Model 322 can store one program of 80 steps, while the 324 has double the capacity arranged as two independent 80-step programs. The programs are entered from the keyboard, with no provision for review or editing. If a mistake is made, the process must be repeated from the beginning. The programs are stored in RAM and disappear when the machine is switched off. An external cassette tape drive can be connected to models 325 and 326 to allow programs to be recorded and reloaded as required.

In spite of these limitations, Compucorp's programmable battery-powered machines had a major impact on field work in many industries. In surveying, for example, they allowed the majority of calculations to be completed quickly and accurately in the field without needing books of tables or return trips to the office. The machine illustrated was purchased and used extensively for field work by a firm of surveyors in Melbourne.

By way of comparison, Hewlett-Packard's first portable calculator, the HP-35, was also released in 1972. The HP-35 had similar numeric range and accuracy, but significantly fewer advanced functions and no programming capability - but it could be carried in a (largish) shirt pocket rather than a briefcase. In 1975 the HP-25 provided equivalent functionality to the Compucorp in a truly pocket-sized machine, and in 1976 the HP-25C with "Continuous Memory" provided non-volatile program storage.

A more detailed description of the Compucorp 320 series "Micro Scientist" series is available in the Technical Section.

C325 External View Compucorp Model 325 "Alpha Scientist", S/N 5256964
Functions: Scientific, programmable
Programming: Keyboard or external cassette tape drive
Technology: MOS-LSI (TI/AMI, 8 chips)
Display: 12+2 Panaplex display, 18-column impact printer
Dimensions: 290W x 350D x 110H, weight 6.2kg
Manufactured: Computer Design Corporation, Los Angeles, 1974

The Compucorp Model 325 "Alpha Scientist" is an enhanced desktop version of the "Micro Scientist" above. The machine uses the same MOS-LSI chipset as the rest of the 300 series, and includes both a Panaplex numeric display and an internal 18-column impact printer. The firmware provides all of the standard functions of the earlier machines, plus some statistical functions and English/Metric conversions.

The Model 325 has an advanced programming capability which includes labels, nested subroutines (six levels), and conditional branching. Programs and register data can be stored as files on a Model 392 cassette tape drive, which attaches via a single DB-25 connector. The tape drive can be controlled from within a program, allowing the machine to automatically load program overlays and handle significant quantities of data.

The 300-series chipset has been re-arranged onto three small boards (90 x 180mm) in the lower section of the machine, with a larger keyboard and display driver board in the upper section. There are five 40-pin chips on the CPU board, 2 on the keyboard and display board, and one on the printer board. The memory board has four 28-pin program ROMs and eight Intel 2102 (1k x 1) static RAMs.

The Model 325 was supplied with a comprehensive 200-page reference manual (dated 1974), and has a pull-out quick-reference card under the keyboard.

The machine illustrated was originally used for programmed statistical calculations at an Australian university.

View with 392 tape drive (25kb)
Internal view (26kb)
Operator's view (58kb)


Resources for further information

Original text and images Copyright © John Wolff 2002-18.
Use at own risk; beware of errors; suggestions for improvement welcome.
Page Created: 30 June 2002
Last Updated: 9 September 2018

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