Define 2 1/2 D memory organization.

In 2 1/2D memory organization, the cells are placed in a two-dimensional array of rows and columns. The address is split into two halves. A row decoder selects one row, and a column decoder selects one column. The cell at the crossing is accessed. Two small decoders of about $2^{n/2}$ outputs each are used, instead of one big decoder of $2^n$ outputs. This reduces the cost and area of the memory chip.