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History of ABACUS

The first ABACUS (Data General 1200)

(Thanks to The Jim Austin Computer Collection and Carl Friend's Minicomputer "Museum" for these two pictures)

ABACUS 4 is the latest of a line which started in the early 1970's. The first ABACUS systems ran on DATA GENERAL 1200 minicomputers with 32 Kb (later 64 Kb) of main (yes ferrite core) memory, and no magnetic disks! Operators could change setpoints etc. via specially constructed 'Operators panels' with seven segment displays and buttons. A KSR 110 baud printer complete with paper tape reader and punch was used for the engineering interface. (An engineers or 'command' panel was used at one stage, but was found to be too expensive, and inflexible and so was discontinued). There were software blocks for process I/O (analog inputs, digital inputs and outputs and pulse duration outputs for process control) logic (checklist, switch and pattern blocks) and process control was done with the 'control' block. Later logging blocks of various sorts were added when text and semigraphic displays appeared and replaced the first panels. All numerical calculations were performed in 16 bit 'fixed point' decimal or integer format.

The process I/O was custom made and was driven directly by cards mounted in the computer. External isolation mudules made for a robust if rather expensive process I/O system. The analog input system used the flying capacitor technique later employed in the PI-Bus system.


In the early 1980's ABACUS II was born. This system ran under the RSX11M operating system on PDP 11 minicomputers. First PDP 11/23, then PDP 11/73. The first systems was diskless, but the majority had 10, 30 and then 70 Mb disks used for the operating system and historical/trend data storage in addition to data dumping. These systems were used to control paper machines steam generating boilers and various other industrial applications.

Some new blocks were added, but the 16 bit 'fixed point' decimal or integer format, whilst altered from +/- 255.99 to +/- 327.67, remained. This was important for speed of execution in the days when floating point processors added significant cost!

The process interface used was Bristol Babcock's PI-Bus. This was developed to serve several different processors each having a different 'bus converter' card. PI-Bus was in fact used on the last of the original ABACUS systems.

PI-Bus is a bus system built around a double height 19 inch Euro rack. 18 cards per rack. Digital input and output cards accommodate 16 signals per card, analog inputs have 8 'flying capacitor' inputs on each multiplexor card in addition two extra cards (Analog Input Controller Card AICC, and Calibration card).


In the early 1990's ABACUS was completely rewritten in C and implemented using the VMS operating system and became VAX ABACUS. Floating point numbers and the ability to reconfigure the number of each block type without recompilation were new features of this system. The operators interface was the Bristol Babcock Enterprise. The Server half of which ran on the same VAX machine, and one or more external PCs running OS/2 supported the Enterprise Windows operator station. Process I/O was the distributed SIOX system from Telefrang AB. PI/Bus was connectable as an upgrade to PDP systems.


ABACUS 4 started as a porting of VAX ABACUS to Linux (the free Un*x operating system found on a large number of Internet servers around the world). New process I/O drivers have been added, most notably for the Computerboards DAS08 series of IDE cards, and the Indata distributed uPLC range.  An interface to MODBUS means that many other systems can be used for process IO. A new graphical engineers tool (engdraw) has been implemented allowing design, implementation, and documentation of the control scheme from one and the same X based program.

ABACUS 4 / Linux will run on any supported intel based computer hardware, thus reducing hardware costs benefiting from large scale mass production. Hardware being easily second sourced, and replaced with commercially available equipment in emergencies.

The operator interface may be either an existing Enterprise Server/Windows, or an X based display system.

Page updated by Frank McNamara abacus_pb.gif .
A member of the MCH-Systems Group