64 bit

64 bit is a term used to describe a computer architecture based around an arithmetic and logic unit (ALU), registers, and [data bus]? which are 64 bits wide.

64-bit processors are quite common, e.g. [Digital Alpha]?, versions of [Sun SPARC]?, and the [IBM AS/4000]?. The PowerPC and Intel are expected to move to 64 bits at their next generation - [PPC 620]? and Intel's IA64?.

A 64-bit address bus allows the processor to address 18 million gigabytes as opposed to the mere 4 gigabytes allowed with 32 bits. Floating point calculations can also be more accurate.

Often mixed architectures are used: with [32 bit]? integer/addresses and 64bit floats.

Taking full advantage of a 64-bit CPU requires a A 64-bit operating system, but backward-compatible architectures can also run a 32-bit OS. For example, processors based on the AMD Hammer architecture can run Intel x86 compatible software, whereas processors based on IA64 architecture need to use software emulation?.

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Based on material from FOLDOC, used with permission.