Memory array

A memory array is an element for storing values. It takes in an N-bit address input and spits out an M-bit value output.

Depending on the use case (ROM or RAM), modifications are needed for the circuit, detailed on their respective page.

Specification

A memory array can store $2^{N}$ values, each value having M bits. A memory array is usually specified by the number of elements times the width of each value.

For example, if N = 10 and M = 12, we have a 1024x12 memory array.

Construction

Memory arrays are usually active lows since not gates are conveniently used for merging memory (see section below). Commercially, there may be an active high enabler.

Merging memory

You can make a bigger memory array with smaller memory arrays. Just enable the one you want according to the address.

A tri-state buffer can be used to control the output enable and write enable

Merging I/O

Traditionally computers have an address bus and a data bus, and we sometimes write and sometimes read. Tri-state buffers can be used to do this.

Timing

Memory is the bottleneck of computing speed, almost certainly taking more than 1 clock cycle to run. An ideal memory is fast, cheap, and large capacity. The hierarchy goes from cache > main memory > virtual memory.

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