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Definition: memory capacity

The total memory (RAM) that can be added to a computer depends on the address registers built into the CPU. For example, most 32-bit CPUs can address only up to 4 gigabytes (GB) of memory.

The reason the maximum capacity in a 64-bit computer is limitless for all intents and purposes (see chart below) is that 64-bit hardware manipulates (calculates, compares and copies) 64 bits, or 8 bytes, of data at a time. However, the actual memory is addressed with far fewer bits. Look up the number 64 in binary values, and note that a 64 bit register could address 16 exabytes of memory, which is 16 million terabytes. See memory.

          Maximum    Processed
  CPU     Memory   Simultaneously

   8-bit   65KB       1

  16-bit    1MB       2

  32-bit    4GB       4

  64-bit    **        8

 ** Limitless for all intents
    and purposes.  No computer can
    be built to accommodate the
    64-bit theoretical maximum.
    See binary values.