The sentinel: IBM System/7

The IBM System/7 was introduced to the world 35 years ago as a rugged and highly reliable computer that could measure, test, analyze and control industrial and laboratory events as they occurred. The sensor-based system, which rented for as little as $352 a month, was IBM's lowest-cost computer at the start of the 1970s.

It was designed to provide a modular approach to sensor-based data processing applications for the stand-alone user (with a system dedicated to a single application) as well as the complex system user (with several IBM computers interconnected in a plant- or company-wide network).

The IBM System/7 was made up of a processor module (the IBM 5010), input/output modules (the IBM 5012 multifunction module, IBM 5013 digital input/output module, IBM 5014 analog input module and IBM 5022 disk storage module), and an operator station (IBM 5028). The processor module and from one to 11 input/output modules were housed in enclosures (IBM 5026) that also provided internal power supplies, signal distribution, and an operator console.

The system's growth could be achieved easily by adding input/output modules to expand sensor attachment capability, and the computer's all-monolithic memory could also be expanded on site.

A host computer attachment allowed the System/7 to operate with an IBM 1130, an IBM 1800, most models of the IBM System/360 or an IBM System/370 for additional input/put and computational capability.

The System/7 had a main memory made entirely of monolithic circuits, which contributed greatly to the system's compactness, reliability and high internal speeds.

To store data and instructions, the computer used silicon chips rather than the magnetic cores that were the convention at the time. Those chips measured less than one-eighth of an inch square and contained 1,434 microscopic elements. Logic circuits in the system were also monolithic, making possible switching speeds from eight to 12 nanoseconds (billionths of a second).

Numerous remotely located sensing devices -- such as gauges and instruments which recorded changes in temperature, humidity, pressure or flow -- could be attached directly to the System/7. As many as a quarter-million readings per second could be recorded and analyzed almost instantaneously by the system. The computer could then generate signals required to control the equipment used in manufacturing and laboratory processes.

The low-cost System/7 provided unattended continuous process control in industrial plants and other rugged environments.The low-cost System/7 provided unattended continuous process control in industrial plants and other rugged environments.

Input such as temperature variations, hygrometer readings and fluctuations in pressure were termed analog data. The System/7 measured those analog quantities and converted them into computer-compatible form (binary numbers). The computer then generated the proper signals to control the equipment, e.g., turn on a switch or adjust a valve.

In the System/7, the IBM 5014 analog input module was available in two versions, one with scan speeds of up to 200 points per second; the other operating at scan speeds up to 20,000 points per second.

The IBM 5012 multi-function module provided analog input/output, digital input/output with process interrupt, and control devices of the IBM 2790 data communication system. (The interrupt feature meant that the system's processor could be programmed to accept and respond to priority instructions. For example, should the signals from a gauge indicate a danger point, the system would interrupt what it was doing, send a signal to remedy the condition, and then return to its program.)

The operator station consisted of a typewriter-like keyboard and request key, printer, paper tape reader and paper tape punch. Operation of those devices was under program control. Push button switches disconnected the station from the system and permitted it to be used as a source program preparation device.

Two methods of preparing programs for the System/7 were provided by MSP/7, a set of modular systems programs. The set included the IBM System/7 Assembler, which loaded into the computer via the paper tape, and allowed the user to write programs at the operator station.

The second method was called Host Preparation Facility and included a library of sensor-based subroutines that a larger IBM computer could use to prepare programs for the System/7.

A new disk module -- the IBM 5022 disk storage module -- was rolled out in July 1971 to significantly enhance the storage capacity and flexibility of the System/7. And two years after that, the company launched a new, larger-capacity model of the System/7, along with enhanced communications and stand-alone programming capabilities, which together broadened the scope of the system's sensor-based applications. The new model's significantly expanded memory of up to 65,536 words could allow users in a wide range of industries to run either several small applications or a single large one without the need for a host computer.

Computer historian Emerson Pugh and his co-authors wrote of the System/7 that:

To learn more about this interesting computer, a visit the System/7 Reference Room will start you on your way.


* IBM's 360 and Early 370 Systems. Emerson W. Pugh, Lyle R. Johnson and John H. Palmer. (Cambridge, Mass.: The MIT Press, 1991), pp. 586-7.

System/7 details