MODIFIED SNAPSHOT PRIORITY ENABLING TWO REQUESTORS TO SHARE A SINGLE MEMORY PORT

In an n-wide (n nominally equals 4) snapshot priority network apparatus the access of n+1 requestors to a memory unit is prioritized. Two requestors--the lowest priority one of normal system requestors called instruction processors plus a maintenance exerciser type requestor--share a single memory port which is nominally the lowest priority one of n such prioritized ports. Requests from both requestors are both honored upon a single priority snap, the instruction processor request nominally proceeding before the maintenance processor request. Although the n-wide priority network remains generally faster than any (n+1)-wide priority network, the maintenance exerciser type requestor is expediently serviced and cannot be locked out of access to memory by the competing higher priority requests of the instruction processor.