Random access

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Random access refers to memory (either main memory, or secondary storage) which has the characteristic that two sequential (in time) operations can go to disparate addresses without significant delays; in sequential access memories, only successive operations to following locations can be done without a time penalty.

Several early main memory technologies (delay lines and drums) did not have this characteristic, although the short-lived Williams tube did.

In secondary storage, magnetic tape is sequential only; disk is a mixture of sequential and random (although fixed-head disks are sequential only within a track; head selection can be random.)