Memory array

Also called: cell array, storage array, memory matrix

The grid of memory cells inside a memory chip, with one row per word line and one column per bit line, selected by the address decoders.

Inside every memory chip is a rectangular grid of cells: the memory array. Everything else on the chip, the decoders, sense circuits and buffers, exists to reach into it.

In the simplest picture:

each row is one word, with its own word line from the address decoder
each column is one bit position, with a bit line running to the data lines

So a 1K × 8 memory is conceptually 1024 rows of 8 cells.

Think of memory as an array in the programming sense, too: a list of words numbered 0, 1, 2, … where the address is the index and the word is the element. The index is fixed; the element is whatever was last written.

Real chips reshape the array to keep it roughly square, so long thin arrays don't need giant decoders. Each physical row may hold several words, and a column decoder picks the right bits from the row: that's two dimensional decoding.

Worked example

Example

Reshaping an array

A 1024 × 1 memory is to be laid out as a square grid.

1.
1024 = 2¹⁰ cells.
2.
Square: 2⁵ × 2⁵ = 32 rows × 32 columns.
3.
Five address bits choose the row (a 5-to-32 decoder), and five choose the column.
4.
Logically it's still 1024 words of 1 bit.

Common mistakes

Confusing the logical shape (words × bits) with the physical grid. A chip can lay its cells out differently from its organization.
Thinking the address is stored in the array. Only the data is; the address is just the position.

Practice Memory array

Interactive questions with instant feedback and a worked solution for every wrong answer.

Memory lesson full course

In a memory, what is the difference between an address and the data at that address?

Learn it step by step

Memory array is taught in Memory.

Memory →

All terms