Random access
From Computer History Wiki
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.)
