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IBM 5100

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The IBM 5100 Portable Computer was a desktop computer introduced in September 1975, six years before the IBM PC. A single integrated unit provided the keyboard, five-inch CRT display, tape drive, processor, several hundred Kbytes of read only memory containing system software, and up to 64 K of random access memory. It was the size of a small suitcase, weighed about 55 lb (25 kg), and could be transported in an optional carrying case, hence the "portable" moniker.

While the IBM 5100 seems large today, in 1975 it was an amazing technical accomplishment to package a complete computer with a large amount of ROM and RAM, CRT display, and a tape drive into a machine that small. Earlier desktop computers of approximately the same size, such as the HP 9830, did not include a CRT nor nearly as much memory. An equivalent late-1960's IBM computer would have been nearly as large as two desks and would have weighed about half a ton.

Available in 12 models providing 16 K, 32 K, 48 K or 64 K positions of main storage, the 5100 sold for between $8,975 and $19,975. The 5100 was available with either APL or BASIC — or both — programming languages.

Machines that supported both languages provided a toggle switch on the front panel to select the language. When the engineers at IBM asked one beta tester, Donald Polonis, for his analysis, he commented that if folks had to learn APL to use it, the IBM 5100 would not make it as a personal computer. He tried to impress the fact that a personal computer had to be easy to use to be accepted.

IBM offered three Problem-Solver Libraries, contained in magnetic tape cartridges, with the IBM 5100 to provide more than 100 interactive routines applicable to mathematical problems, statistical techniques and financial analyses.

The IBM 5100 is based on a microprocessor called PALM (Put All Logic in Microcode). IBM used the term "microprocessor" to mean a processor that executes microcode to implement a higher-level instruction set, rather than its conventional definition of a complete processor on a single silicon integrated circuit. The PALM processor was an entire circuit board containing 13 square metal-can bipolar gate arrays, 3 conventional DIP transistor-transistor logic (TTL) parts and 1 round metal can part. The IBM 5100 Maintenance Information Manual also referred to this board as the controller.

Unlike modern processors the microcode was stored in ROM, called the Control ROS (Read Only Storage). This allowed cost effective porting of the 32-bit microcode of larger processors to the 16-bit PALM. Note that although the processor was capable of addressing 16-bits only, the databus was actually 18-bits. 1 bit per (9-bits) byte was used for parity. To address more than 64 K the PALM used bank switching.

The 5100 allowed to connect an external TV using a BNC connector, allthough only bright on a black blackground. It appears that the American 60 Hz norm is supported and not 50 Hz. This must have caused some trouble for European and other countries.

Also in September 1975 IBM announced the IBM 5100 Communications Adapter. That allowed the 5100 to transmit data to and receive data from a remote system. It made the 5100 appear the same as an IBM 2741 Communications Terminal and in theory was able to communicate with IBM 2741 compatible machines in start-stop mode using the EBDC (extended binary coded decimal) notation. Unfortunately the EBCD characterset used didn't fully comply with the EBCD standard. That limited the use of this feature. Note that IBM explicitly used the abbreviation EBCD in the manuals and not the more commonly known EBCDIC.

In Volume 16, Number 1, Page 41 (1977) of the IBM Systems Journal the article "The IBM 5100 and the Research Device Coupler — A personal laboratory automation system" read: "A small laboratory automation system has been developed by using the IBM 5100 Portable Computer in conjunction with the Research Device Coupler. This compact system provides a dedicated, high-level-language computer and a versatile data acquisition and control interface for experiments in which data rates do not exceed 9600 Baud. Two experiments exemplify the use of the system. The Research Device Coupler described in this paper is a prototype of the IBM 7406 Device Coupler."

The 5100 was withdrawn from marketing in March 1982. In January 1978 IBM announced its successor: The IBM 5110.

See also

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