Abstract: Apparatus for arbitrating between requests from a plurality of sources for access to a shared resource, the apparatus comprising: a register means having a plurality of stages, each stage containing a designation of one of said sources, a plurality of stages containing a designation of the same source, logic means for accessing the register stages according to a priority scheme and for comparing the designation in each stage with requests for access, and granting access according to the match between the highest priority source designation and a memory request, and means for changing the contents of the register means subsequent to access grant.