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The Transputer

The INMOS Transputer was a pioneering parallel computing processor of the 1980s from the Welsh chip design company INMOS. It the first general purpose microprocessor designed specifically to be used in parallel. The design of the Transputer included serial links that allowed it to communicate with up to four other Transputers.

Transputer instructions comprised 8-bit words broken into two 4-bit nibbles. The high-order nibble contained the instruction code. The "lower" nibble contained data, either for arithmetic operations, for addressing memory, or as an operand to the indirect opcode, which was used to add more instructions to those available using the the 16 possible using a nibble. Of the 16 opcodes available, 3 were set aside for special purposes: one was "prefix", and added a new nibble to the current data item; one was negative-prefix, performing the same function as prefix but providing a negative rather than positive value, and one was operate, which took the currently assembled value and used it as an opcode. This scheme permitted a very dense instruction format, with as many as 4 useful instructions possible in a single 32-bit memory word. The normal average was a little over 2, because of the need to load constants in more than one operation.

One big advantage of this scheme was that it permitted 16 bit and 32-bit transputers to share the same binary format and, in many cases, the same compiled programs.

A great deal more information about transputers is available at these two websites: The wikipedia entry provides a very good basic introduction, with some of the history of the device, and the second (Transputers - extinct but not forgotten) entry is a much more technical introduction to the devices:

  1. Wikipedia online encyclopedia entry
  2. Transputers - extinct but not forgottenby John Catsoulis

There are a number of other links to transputer related sites on the WoTUG Links page.


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