64-bit

    A term describing a computer architecture with an
ALU,
   registers and data bus which handle 64 bits at a time.

   64-bit processors were quite common by 1996, e.g. Digital Alpha,
   versions of Sun SPARC, MIPS, IBM AS/4000.  The PowerPC
and
   Intel were expected to move to 64 bits at their next generation -
PPC
   620 and Intel P7.

   Being able to deal with 64-bit binary numbers means the
   processor can work with signed integers between +-2^32 or
   unsigned integers between zero and 2^64-1.  A 64-bit address
   bus allows the processor to address 18 million gigabytes as
   opposed to the mere four gigabytes allowed with 32 bits.  In
   1996 hard disks could already hold over 4 GB.  Floating
   point calculations can also be more accurate.

   A 64-bit OS is needed as well to take advantage of the CPU.
   In 1996 there were only a few 64-bit operating systems,
   including OS/400, Digital Unix, Solaris (partialy).  A
   32-bit OS can run on a 64-bit CPU.

   (2004-05-12)