Hewlett-Packard 4955A Protocol Analyzer  
Written by Accutron on 2006-10-10  

The Hewlett-Packard 4955A is an obscure cousin of the HP 9825 desktop calculator, a minicomputer-class system used extensively in scientific and engineering fields in the 1970s. Instead of being built for arithmetic and programming, the 4955A is optimized for network analysis, research and development. The 4955A is built upon the HP 5061-3011 16-bit hybrid microprocessor, equivalent to an enhanced HP 2100-series minicomputer on two NMOS dies.

4955A Datasheet (PDF)
Protocol Analyzer Comparison Sheet (PDF)

HP originally adapted their 2100-series minicomputer architecture for use in desktop scientific calculators, initially in the 9810/20/30 series, which employ a serialized adaptation of the 2114A CPU. The subsequent 9825A/B calculator and its descendants use a single-chip NMOS adaptation of the 2100 series architecture. This microprocessor would later be used in various computerized test equipment, including the 4955A Protocol Analyzer pictured here.

In addition to the 5061-3011 hybrid microprocessor, the 4955A also makes use of the 5061-3012 tape drive controller, originally designed for the 9825-descendant HP 9845. The 4955A also contains a massive amount of support hardware not present in the 9825 or its more immediate relatives, including dozens of EPROMs.

The 4955A is built as a huge rack-mountable lunchbox, with a hinged flip-down keyboard and built-in high resolution monochrome green CRT. Powering up the 4955A is very satisfying, with its loud cooling fan and highly nostalgic startup pings. The tape drives also make interesting noises when reading/writing. There are several LEDs visible with the rear cover open, that display some sort of diagnostic information. The 4955A also has one of the best development codenames ever: Cookie Monster.

Hewlett-Packard 4955A Protocol analyzer, shown with RS-232 pod.

4955A, tape drive card featuring the 5061-3012 tape drive controller.

4955A, tape drive card removed to reveal the hybrid microprocessor motherboard.

4955A, rear panel removed, showing the card cage bound tightly with ribbon cable.

This article is part of the [Electronic Test Equipment] exhibit.

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