128-bit

In computer architecture, 128-bit integers, memory addresses, or other data units are those that are at most 128 bits 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. The sixth generation of game consoles, released in 2000 and 2001 and including the Playstation 2, GameCube and Xbox, is sometimes incorrectly referred to as "the 128-bit era" as the Gamecube and Xbox both used 32-bit CPUs, while the Playstation 2 used a 64-bit CPU. As of January 1, 2008, no video game consoles using 128-bit CPUs have been announced.

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 stored now. 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. However, even if Moore's law were to apply to memory size (and probably also memory access speeds) in the years to come – a big assumption – it would still take a long time to exhaust a 64-bit address space. A doubling of memory capacity requires one extra address bit. Considering that large servers available in mid-2006 contain 512 GiB of RAM, then a 64-bit address space should be sufficient for another 50 years. For comparison, electronic computing was invented only about 60 years ago.
• Many modern graphics cards have 128-bit or 256-bit memory busses.
• 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 addresses 64 bits of memory. 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.