Hewlett-Packard 21MX / 1000 M-Series  
Written by Accutron on 2009-07-07  

After the 2100A and 2100S, HP released the 21MX series, believed to be the industry's first minicomputers to be equipped with semiconductor RAM. The original 21MX series from 1974 consists of three models of ascending size and expansion capacity: 2105A, 2108A and 2112A.

The 2108B (pictured here) and 2112B were added to the series in 1976, the most notable improvement over the 'A' variants being the relocation of the power switch from the rear of the CPU to a more traditional and accessible location behind the lockable front panel.

In 1976, HP released the improved 21MX E-Series, renaming the original 21MX computers as 21MX M-Series to distinguish them from the E-Series systems. When HP released the third generation of 21MX systems in 1978, the naming convention was changed once again. These new systems were named 1000 F-Series, and the older 21MX systems were renamed as 1000 M-Series and 1000 E-Series to maintain conformity.

1000 M-Series Installation & Service Manual (PDF)

All of the marks of progress can be seen when comparing the 2108B to one of its predecessors, such as the 2114B. The 2108B is faster, quieter, smaller, and constructed of thinner sheet metal. The most severe difference between the 2108B and the 2114B is the presence of LSI semiconductor RAM, rather than the 2114's magnetic core memory. The 21MX line of computers is believed to be the first minicomputer architecture to use semiconductor RAM.

The computer featured in this exhibit was probably built in 1978, based on the front panel artwork, which changed over the course of the 21MX-series lifespan. Early machines were labeled as 21MX Computer Series, while later examples are labeled as HP 1000 M-Series.


Hewlett-Packard 2108B minicomputer, serial number 2440A02933. This computer was originally owned by General Dynamics, and was used in the F-16 Fighting Falcon development program in the late 1970s.


2108B, front panel open. Note the power switch location, unique to the 'B' variant.

HP Computer & Calculator Products (1966-1976)

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

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