text: In computer architecture, 64-bit is an adjective used to describe integers, memory addresses or other data units that are at most 64 bits (8 octets) wide, or to describe CPU and ALU architectures based on registers, address buses, or data buses of that size.\n\n\nAs of 2004, 64-bit CPUs are common in servers, and have recently been introduced to the (previously 32-bit) mainstream personal computer arena in the form of the AMD64, EM64T, and PowerPC 970 (or "G5") processor architectures.\n\nAlthough a CPU may be 64-bit internally, its external data bus or address bus may have a different size, either larger or smaller, and the term is often used to describe the size of these buses as well. For instance, many current machines with 32-bit processors use 64-bit buses (e.g. the original Pentium and later CPUs), and may occasionally be referred to as "64-bit" for this reason. The term may also refer to the size of an instruction in the computer's instruction set or to any other item of data (e.g. 64-bit double-precision floating-point quantities are common). Without further qualification, however, a computer architecture described as "64-bit" generally has integer registers that are 64 bits wide and thus directly supports dealing both internally and externally with 64-bit "chunks" of integer data.