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The Computer Journal 1967 10(1):64-68; doi:10.1093/comjnl/10.1.64
© 1967 by British Computer Society
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Competition for memory access in the KDF9

C. S. Wallace and B. G. Rowswell *

Basser Computing Department, School of Physics, University of Sydney, Sydney, Australia

The I/O control of a computer may adopt various strategies for serving competing requests from peripheral channels for access to a single core memory. The strategy adopted places some limit on the peripheral configurations which may be simultaneously active. An "ideal" strategy is exhibited which imposes no constraint other than that implied by the finite speed of the core memory, but it is expensive to implement. Limits on configurations are derived for the ideal, first come-first served, round-robin and priority systems. It is shown that the first come-first served and round-robin systems have little or no advantage over a random choice. The KDF9 at the University of Sydney, which was delivered with a first come-first served system, has been modified to incorporate a priority system. The new system uses 48 fewer circuit boards, but allows the attachment of high-rate channels which otherwise could not be accommodated.


* Basser Computing Department, School of Physics, University of Sydney, Sydney, N.S.W., Australia.


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