128-bit

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In computer architecture, 128-bit integers, memory addresses, or other data units are those that are at most 128 bits 16 octets wide. Also, 128-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size.

There are currently no mainstream general-purpose processors built to operate on 128-bit integers or addresses, though a number of processors do operate on 128-bit data. System/370, made by IBM, could be considered the first rudimentary 128-bit computer as it used 128-bit floating point registers. Most modern CPUs such as the Pentium and PowerPC have 128-bit vector registers used to store several smaller numbers, such as four 32-bit floating-point numbers. A single instruction can operate on all these values in parallel (SIMD). They are 128-bit processors in the sense that they have 128-bit registers and in some cases a 128-bit ALU, but they do not operate on individual numbers that are 128 binary digits in length.

Uses

• IPv6 addresses are 128 bits wide. Having a processor capable of manipulating 128-bit integers could simplify handling of IPv6 addresses, since addresses could be stored in a single register, much as IPv4 addresses are manipulated in 32-bit computers. See also RFC 1924 section 7.
• 128 bits is a common key size for symmetric ciphers in cryptography.
• 128-bit processors could become prevalent when 16 exbibytes of addressable memory is no longer enough (128-bit processors would allow for 274,877,906,944 yottabytes of memory).
• Quadruple precision (128-bit) floating point number can store qword (64-bit) fixed point number or integer accurately without losing precision.
• Many modern graphics cards have a 128-bit or 256-bit data bus to memory.
• Sony's Playstation 2 CPU Emotion Engine is advertised as a 128 bit processor. It has 128-bit SIMD registers, like many processors, but is only a 64-bit processor in the traditional sense as it can only use 64-bit memory addresses. Most high-end CPUs today have 64-bit memory address; there are only very few true 128-bit supercomputer chips.
• The AS/400 virtual instruction set defines all pointers as 128-bit. This gets translated to the hardware's real instruction set as required, allowing the underlying hardware to change without needing to recompile the software. Past hardware was 32-bit CISC, while current hardware is 64-bit PowerPC. Because pointers are defined to be 128-bit, future hardware may be 128-bit without software incompatibility.