Honeywell 200

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System console, left, (shown with IBM 1402 card reader/punch).
Closeup of system console. After a program was loaded, the value of individual memory locations could be altered using the console buttons.

The Honeywell 200 was a character-oriented two-address commercial computer introduced by Honeywell in the early 1960s, the basis of later models including 1200, 1250, 2200, 3200, 4200 and the later 2070, and the character processor of the Honeywell 8200.

Introduced to compete with IBM's 1401, the H200 was two or three times faster and, with software support, could execute IBM 1401 programs without need for their recompilation or reassembly. The Liberator marketing campaign exploited this compatibility, and was credited in later Honeywell publicity statements with stalling the sales of IBM 1401 machines. Honeywell claimed an initial rush of hundreds of orders for the H200 that itself stalled when IBM countered with a marketing emphasis on their System 360 product range that was then under development.

Architecture[edit]

As designed by Director of Engineering William L. Gordon, the H200 memory consisted of individually addressed characters, each composed of six data bits, two punctuation bits and a parity bit. The two punctuation bits recorded a word mark and an item mark, while both being set constituted a record mark. The item bit permitted item moves and record moves in addition to word moves (move successive characters one-by-one starting at the addresses given in the instruction, stopping when the relevant punctuation mark was found set in either field).

An instruction consisted of a one-character op-code, up to two operand addresses and an optional single character variant. Usually the op-code character would be word-marked, confirming the end of the previous instruction. An item-marked op-code would be handled differently from normal, and this was used in the emulation of IBM 1401 instructions that were not directly compatible. The first three bits of an operand address could designate one of six index registers that occupied the first 32 addressable memory locations. The other two possible bit patterns indicated no indexing, or indirect addressing.

A Change Address Mode (CAM) instruction switched between 2-, 3- and 4-character address modes. The address mode specified the number of characters needed for each operand address in instructions.

A Change Sequence Mode (CSM) instruction stored the next instruction address in a memory location and loaded the instruction counter from another memory location. This provided a simple switch between threads within a program, similar to the sequence/cosequence behaviour of the Honeywell 800 series.

While the H200 supported operation with just a console, card reader and punch like the IBM 1401, the generic Input-Output instructions also supported line printers and magnetic tape drives.

IO instructions left punctuation bits unchanged, reading or writing only data (and parity) bits into memory, and terminating on any record mark encountered. A record mark could be placed at the end of an input buffer to prevent any buffer overflow, a problem that was to persist in many other systems into the 21st century.

The 200-series IO instructions were a Peripheral Data Transfer (PDT) and a Peripheral Control and Branch (PCB) that explicitly implemented asynchronous IO. The PDT specified a device address, a buffer address and the transfer operation to be started, while the PCB specified a device address, and set the operating mode or tested the status of the device. Both used the format Op-code Address I/O unit address Variant.

Software[edit]

The native assembly language was named Easycoder.

The Easycoder assembler generated an object file as a binary card deck that could be punched to cards or written to magnetic tape instead. The object file began with a bootstrapping routine so that each program could be loaded into memory, from card reader or magnetic tape, using a boot command from the console.

The H200 was commonly used as a spooling computer associated with a larger Honeywell 800 series machine. The H1800-II consisted of an H1800 mainframe equipped only with magnetic tape drives and an online adaptor (OLA) connection to a satellite H200 to simulate a card reader for reading low volumes of job control cards. The LINK program running on the H200 handled the OLA, copied punched cards or punched paper tape to magnetic tape, and copied records from magnetic tape to card punch or to line printer.

In popular culture[edit]

In 1965 as part of the H200 promotion in the UK, the subsidiary Honeywell Controls Limited commissioned the artist Rowland Emett to construct a whimsical mechanical sculpture called The Honeywell Forget-me-not Computer as part of the company's exhibit at the Business Equipment Exhibition. Honeywell 200 consoles featured in the graphic design of Len Deighton's Billion-Dollar Brain book jacket and also figured as part of the hall-sized supercomputer complex in the 1967 movie of the book starring Michael Caine and Karl Malden. These promotions, plus an Emett calendar, originated in the UK and were the inspiration of Don Hatton, the publicity manager of Honeywell Controls Limited Electronic Data Processing division.

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