The 12-bit ND812, produced by Nuclear Data, Inc., was a commercial minicomputer developed for the scientific computing market.
The programmed I/O bus typically runs low to medium-speed peripherals, such as printers, teletypes, paper tape punches and readers, while DMA is used for cathode ray tube screens with a light pen, analog-to-digital converters, digital-to-analog converters, tape drives, disk drives.
The word size, 12 bits, is large enough to handle unsigned integers from 0 to 4095 – wide enough for controlling simple machinery.
[3] The ND812's basic configuration has a main memory of 4,096 twelve-bit words with a 2 microsecond cycle time.
DMA is accomplished by "cycle stealing" from the CPU to store words directly into the core memory system.
Nuclear Data provided interfaces to the following peripherals: The ND812 did not have an operating system, just a front panel and run and halt switches.
The I/O facility allowed for peripherals to directly load programs into memory while the computer was halted and not executing instructions.
Since core memory is non-volatile, shutting off the computer did not result in data or program loss.
A sample of the assembler from the Principles of Programming the ND812 Computer manual is shown below: NUTRAN, a conversational, FORTRAN-like language, was provided.
Group 1 instructions perform arithmetic, logical, exchange and shifting functions on the accumulator registers.
The ND812 processor provides a simple stack for operands, but doesn't use this mechanism for storing subroutine return addresses.