Hewlett-Packard 2100A  
Written by Accutron on 2013-08-20  

The Hewlett-Packard 2100A is the first iteration of HP's second generation 16-bit minicomputers. The 2100A utilizes the same basic architecture as HP's first generation systems, but is noteworthy as being the first microprogrammable minicomputer, and the first minicomputer with a switching power supply.

The CPU of the HP 2100A and nearly identical HP 2100S are constructed of discrete TTL and CTuL logic ICs, and are the last 2100-series minicomputers manufactured by HP that make use of core memory. The 2100A has a maximum memory capacity of 32K, 14 I/O channels, dual-channel DMA and hardware multiply/divide. Essentially, the 2100A is a maximally upgraded, microprogrammable 2116C, in a chassis less than half the size. The introduction of the 2100A instantly made all previous HP minicomputers obsolete.

Unlike HP's first generation systems, the 2100A entirely omits all register displays (except for the switch register), marking a turning point in the evolution of computers which spread across the entire industry through the 1970s. Without register displays, traditional machine language programming from the front panel would become an impossibility.

The unit pictured here was originally installed as part of a Measurex process control system, and has been re-branded as a Measurex 2650 Central Processing Unit. An internal examination of the computer reveals a custom Measurex external memory card installed in slot A9, a location normally reserved for a genuine HP direct memory access card.

Based in Cupertino CA, Measurex was one of the first companies to develop industrial process control equipment, and their early systems were built around HP 2116 and HP 2100 computers. Measurex was one of HP's largest computer customers, but they had the bad habit of anonymizing or re-branding the HP computers used in their systems. The majority of these early Measurex process control systems were employed in paper mills, a true testament to the near indestructibility of HP's 2100-series minicomputers.

Hewlett-Packard 2100A computer, re-branded as a Measurex 2650 Central Processing Unit. This computer is missing one pushbutton assembly, six lamp covers and all of its core memory cards.

2100A, internal configuration. Note the missing core memory cards in the rear cage.

HP 12539A Time Base Generator card.

Measurex external memory interface card, removed from card slot A9. Slot A9 is normally reserved for an official HP direct memory access card, but the Measurex-modified 2100A adds paged memory, expanding the system to 512K. Special thanks to former Measurex employee John Rayfield for identifying this card.

Measurex MX-1010 process control system.

Measurex MX-1500 process control system.

HP Computer & Calculator Products (1966-1976)

This article is part of the [Digital Computer Equipment] exhibit.

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