Bendix G-15

The series was gradually discontinued when Control Data Corporation took over the Bendix computer division in 1963.

The chief designer of the G-15 was Harry Huskey, who had worked with Alan Turing on the ACE in the United Kingdom and on the SWAC in the 1950s.

He made most of the design while working as a professor at Berkeley (where his graduate students included Niklaus Wirth), and other universities.

It uses the drum as a recirculating delay-line memory, in contrast to the analog delay line implementation in other serial designs.

A consequence of this design was that, unlike other computers with magnetic drums, the G-15 does not retain its memory when it is shut off.

The adders work on one binary digit at a time, and even the instruction word was designed to minimize the number of bits in an instruction that needed to be retained in flip-flops (to the extent of leveraging another one-word drum line used exclusively for generating address timing signals).

Average memory access time is 14.5 milliseconds, but its instruction addressing architecture can reduce this dramatically for well-written programs.

The machine's limited storage precludes much output of anything but numbers; occasionally, paper forms with pre-printed fields or labels were inserted into the typewriter.

The mechanical reader and punch can process paper tapes up to eight channels wide at 110 characters per second.

A problem peculiar to machines with serial memory is the latency of the storage medium: instructions and data are not always immediately available and, in the worst case, the machine must wait for the complete recirculation of a delay line to obtain data from a given memory address.

Users also developed their own tools, and a variant of Intercom suited to the needs of civil engineers is said to have circulated.

The "Intercom" series of languages provide an easier to program virtual machine that operates in floating point.

The machine found a niche in civil engineering, where it was used to solve cut and fill problems.

A Bendix G-15 was still in use for the UC Berkeley extension summer class in programming, at Oakland Technical High School, in 1970.

One of the teaching assistants, a graduate student at UCLA, reported that one was used to check syntax of Fortran programs before they could be submitted to the IBM 7094.

The program began as a six week residential science enrichment course for advanced rising high-school seniors, at the Thacher School in Ojai, California, as a collaboration between the Headmaster, Stanford University, Caltech, and Harvey Mudd College, in response to Sputnik.

The curriculum was focused on astronomy, with a lab project that consists of photographing an asteroid three times and computing its orbit.

Bendix G-15 computer, 2015
A read amplifier module from a G-15