Expansion of word length and capacity (Part 3)

• Expansion of word length

Word length expansion connects memory devices in parallel, so that the address range is unchanged but the data is wider. The number of data units is unchanged, but the size of the data units increases.

Word length expansion usually requires external logic to implement, as the memory devices operate in unison and therefore share all address, data, and control lines.

• Expansion of word Capacity

Memory capacity expansion connects memory devices “end-to-end,” so that the data width is unchanged but the address range increases. The size of the data units is the same, but the number of data units increases.
Memory capacity expansion usually requires some external logic, as only one memory device is active at a time and the system must provide some means of distinguishing the two. Typically an inverter is used on the chip select line on one of the memory devices, so that selecting one will automatically de-select the other.