A term describing a computer architecture based around an ALU, registers and data bus which are 64 Bits wide. 64-Bit processors were quite common in 1996, e.g. DigitalAlpha, versions of SunSPARC, MIPS, IBMAS/4000. the PowerPC and Intel were expected to move to 64 Bits at their next generation - PPC 620 and Intel P7. A 64-Bitaddress bus allows the processor to address 18 million gigabytes as opposed to the mere 4 gigabytes allowed with 32 Bits. There were in 1996 already hard disks which can hold over 4GB. Floating point calculations can also be more accurate. A 64-BitOS is needed as well to take advantage of the CPU. In 1996 there were only a few 64-Bit operating systems, including OS/400, DigitalUnix, Solaris (partialy). A 32-Bit OS can run on a 64-Bit CPU. (2004-05-12)