64-bit

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In computer architecture, 64-bit integers, memory addresses, or other data units are those that are at most 64 bits (8 octets) wide. Also, 64-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size. 64-bit is also a term given to a generation of computers in which 64-bit processors were the norm.

64-bit CPUs have existed in supercomputers since the 1970s (Cray-1, 1975; CDC 6000 series, 1964, were 60-bit) and in RISC-based workstations and servers since the early 1990s. In 2003 they were introduced to the (previously 32-bit) mainstream personal computer arena, in the form of the x86-64 and 64-bit PowerPC processor architectures.

Without further qualification, a 64-bit computer architecture generally has integer and addressing registers that are 64 bits wide, allowing direct support for 64-bit data types and addresses. However, a CPU might have external data buses or address buses with different sizes from the registers, even larger (the 32-bit Pentium had a 64-bit data bus, for instance). The term may also refer to the size of low-level data types, such as 64-bit floating-point numbers.

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