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-bit address 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-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, DigitalUnix, Solaris (partialy). A 32-bit OS can run on a 64-bit CPU. (2004-05-12)
