One-address systems: PDP10

Few of the computers classed as one-address systems have strictly one-address instruction formats, although these were traditionally fairly common among minicomputers and early microcomputers where economy of bits in instructions was vital. The DEC PDP-10 [1], for example, had a single store address within each instruction, but also specified one of sixteen identical, general purpose registers, rather than assuming a single implicit accumulator.

IBM 360 instruction format

Figure 4. PDP 10 instruction format

One-and-a-half-address might be a more appropriate designation for this type of instruction, and clearly the IBM System/360 RX format (described under Two Address Systems) would fall into this category. Instructions in MU5 (see under The MU5 instruction set), on the other hand, and its commercial derivatives, the ICL 2900 series and Series 39, can be regarded as strictly one-address. There are only a few registers, all serving different dedicated purposes, and the register specification is therefore implied by the function code, rather than being explicitly addressed within the instruction format.

An interesting example of a one-address system is the Manchester Atlas.

References

  1. ^ C.G. Bell, A. Kotek, T.N. Hastings and R. Hill
    "The Evolution of the DEC System 10"
    CACM, Vol 21, pp 44-62 1978
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