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. The 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 feature SIMD instruction sets (SSE, AltiVec etc.) where 128-bit vector registers are used to store several smaller numbers, such as four 32-bit floating-point numbers, and a single instruction can operate on all these values in parallel. These are 128-bit processors in the sense that they have 128-bit registers, but they do not operate on individual numbers that are 128 binary digits in length.

- 128 bits is a common key size for symmetric ciphers in cryptography. It is also the size of Globally Unique Identifier and IPv6 address.
- 128-bit processors could become prevalent when 16 exbibytes of addressable memory is no longer enough (128-bit processors would allow memory addressing for 340,282,366,920,938,463,463,374,607,431,768,211,456 bytes (~340.3 undecillion bytes or 281,474,976,710,656 yobibytes ). However, physical limits make such large amounts of memory currently impossible, given that amount greatly exceeds the total data stored on Earth today.
- Quadruple precision (128-bit) floating point number can store qword (64-bit) fixed point number or integer accurately without losing precision. Notice that since the 8087 (1980), x86 architecture supports 80bits float-points that store and process accurately 64bits integers
- 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 32-bit processor in the traditional sense as it can only use 32-bit memory addresses.
- 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.
- Larger bit widths are also commonly seen on the memory interface of graphics processing units, including 128-bit, with some bus widths reaching 512-bits long.
- Increasing the word size can speed up multiple precision math libraries. Applications include cryptography.
- Large word sizes can increase the feasibility of using certain very fast data structures (consider representing a set by having one bit per possible set element). wikipedia

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