Memory Stores

Abstract

Memory stores fall into two main categories: immediate access memory and backup stores. The former may be defined as that to which the elffin can be directed and from which he can either bring back or write in the information immediately, that is, within one operating cycle of the computer (typically less than half a dozen microseconds). Immediate access memories for use with MPUs generally consist of semiconductor integrated circuits (chips), but on earlier computers the information for each bit in store was held by magnetising a small ferrite core. The stores were therefore then generally known as core stores, a name which, although no longer strictly correct, is still sometimes used. The size of the immediate access memory available to an MPU is usually restricted to 2¹⁶ or 65536 bytes. In practice, stores as large as this are seldom if ever used. Systems are usually designed and operate satisfactorily with stores a fraction of this size.