64-bit CPUs have been used in supercomputers since the 1970s ( Cray-1, 1975) and in reduced instruction set computers (RISC) based workstations and servers since the early 1990s. 64 bits is a word size that defines certain classes of computer architecture, buses, memory, and CPUs and, by extension, the software that runs on them. The term 64-bit also describes a generation of computers in which 64-bit processors are the norm. However, not all 64-bit instruction sets support full 64-bit virtual memory addresses x86-64 and ARMv8, for example, support only 48 bits of virtual address, with the remaining 16 bits of the virtual address required to be all 0's or all 1's, and several 64-bit instruction sets support fewer than 64 bits of physical memory address. A computer that uses such a processor is a 64-bit computer.įrom the software perspective, 64-bit computing means the use of machine code with 64-bit virtual memory addresses.
Also, 64-bit CPUs and ALUs are those that are based on processor registers, address buses, or data buses of that size.
In computer architecture, 64-bit integers, memory addresses, or other data units are those that are 64 bits wide.
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