GRANUALITY (MEMORY)

2/27/99

Granularity (Memory): RAM granularity refers to the size of the smallest incremental units of RAM. One affect is a difficulty building small memory units from large capacity integrated circuits. For example, a 64MegaByte RAM that is only 1 bit wide, can only be used to build 64, 128, 196, etc Megabyte memories. Memory ICs are available in widths greater than 1 bit, but there are good technical reasons to avoid very wide DRAMs. And some performance enhancing techniques such as interleave require RAM to be organized into autonomous units. Thus an interleaved 8 bit wide RAM must be constructed from 1, 2 or 4 bit wide units

The granularity problem is especially evident with Dynamic RAM where the lowest cost per bit is encountered with the largest RAMs. Granularity may well be an issue in future computer design. It has been conjectured that home and consumer computers will tend to use RDRAM which comes in smaller, wider sizes whereas larger computers may use SDRAM which comes in large, narrow units.

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