332. 128-bit

128-bit

Processors            4-bit

8-bit

12-bit

16-bit

18-bit

24-bit

31-bit

32-bit

36-bit

48-bit

60-bit

64-bit

128-bit

Applications                32 bit               64 bit               128 bit

Data Sizes                   nibble   octet   byte   word   dword   qword                                        

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 IBM System/370 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.

However, these processors do not operate on individual numbers that are 128 binary digits in length, only their registers have the size of 128-bits.

The DEC VAX supported operations on 128-bit integer ('O' or octaword) and 128-bit floating-point ('H-float' or HFLOAT) datatypes. Support for such operations was an upgrade option rather than being a standard feature. Since the VAX's registers were 32-bits wide, a 128-bit operation used four consecutive registers or four longwords in memory.

Uses

• 128 bits is a common key size for symmetric ciphers in cryptography. It is also the size of Globally Unique Identifiers and IPv6 addresses.
• 128-bit processors could become prevalent as a method of addressing over 2^64 bits of information. Up to 2^128 could be directly addressed with 128 bits. That amount greatly exceeds the total data stored on Earth today (2010), which has been estimated to be around 1.2 zettabytes (over 2⁷⁰ bytes).
• Quadruple precision (128-bit) floating point numbers can store qword (64-bit) fixed point numbers or integers accurately without losing precision. Notice that since the 8087 (1980), x86 architecture supports 80-bit floating points that store and process 64-bit signed integers (-2⁶³...2⁶³-1) accurately.
• 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.
• Increasing the word size can speed up multiple precision math libraries. Applications include cryptography.