128-bit
Encyclopedia
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
SIMD
Single instruction, multiple data , is a class of parallel computers in Flynn's taxonomy. It describes computers with multiple processing elements that perform the same operation on multiple data simultaneously...

 instruction sets (SSE
Streaming SIMD Extensions
In computing, Streaming SIMD Extensions is a SIMD instruction set extension to the x86 architecture, designed by Intel and introduced in 1999 in their Pentium III series processors as a reply to AMD's 3DNow! . SSE contains 70 new instructions, most of which work on single precision floating point...

, AltiVec
AltiVec
AltiVec is a floating point and integer SIMD instruction set designed and owned by Apple, IBM and Freescale Semiconductor, formerly the Semiconductor Products Sector of Motorola, , and implemented on versions of the PowerPC including Motorola's G4, IBM's G5 and POWER6 processors, and P.A. Semi's...

 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
Processor register
In computer architecture, a processor register is a small amount of storage available as part of a CPU or other digital processor. Such registers are addressed by mechanisms other than main memory and can be accessed more quickly...

 have the size of 128-bits.

The DEC VAX
VAX
VAX was an instruction set architecture developed by Digital Equipment Corporation in the mid-1970s. A 32-bit complex instruction set computer ISA, it was designed to extend or replace DEC's various Programmed Data Processor ISAs...

 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
    Key size
    In cryptography, key size or key length is the size measured in bits of the key used in a cryptographic algorithm . An algorithm's key length is distinct from its cryptographic security, which is a logarithmic measure of the fastest known computational attack on the algorithm, also measured in bits...

     for symmetric ciphers in cryptography
    Cryptography
    Cryptography is the practice and study of techniques for secure communication in the presence of third parties...

    . It is also the size of Globally Unique Identifier
    Globally Unique Identifier
    A globally unique identifier is a unique reference number used as an identifier in computer software. The term GUID also is used for Microsoft's implementation of the Universally unique identifier standard....

    s and IPv6
    IPv6
    Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...

     addresses.
  • 128-bit processors could be used for addressing directly up to 2128 (over 3.40 × 1038) bytes, which would greatly exceed the total data stored on Earth as of 2010, which has been estimated to be around 1.2 zettabyte
    Zettabyte
    A zettabyte is a unit of information or computer storage equal to one sextillion bytes....

    s (over 270 bytes).
  • Quadruple precision (128-bit) floating point
    Floating point
    In computing, floating point describes a method of representing real numbers in a way that can support a wide range of values. Numbers are, in general, represented approximately to a fixed number of significant digits and scaled using an exponent. The base for the scaling is normally 2, 10 or 16...

     numbers can store qword (64-bit) fixed point
    Fixed-point arithmetic
    In computing, a fixed-point number representation is a real data type for a number that has a fixed number of digits after the radix point...

     numbers or integers
    Integer (computer science)
    In computer science, an integer is a datum of integral data type, a data type which represents some finite subset of the mathematical integers. Integral data types may be of different sizes and may or may not be allowed to contain negative values....

     accurately without losing precision
    Accuracy and precision
    In the fields of science, engineering, industry and statistics, the accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's actual value. The precision of a measurement system, also called reproducibility or repeatability, is the degree to which...

    . Notice that since the 8087
    Intel 8087
    The Intel 8087, announced in 1980, was the first floating-point coprocessor for the 8086 line of microprocessors. It had 45,000 transistors and was manufactured as a 3 μm depletion load HMOS circuit. The 8087 was built to be paired with the Intel 8088 or 8086 microprocessors...

     (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
    PowerPC
    PowerPC is a RISC architecture created by the 1991 Apple–IBM–Motorola alliance, known as AIM...

    . 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
    Arbitrary-precision arithmetic
    In computer science, arbitrary-precision arithmetic indicates that calculations are performed on numbers whose digits of precision are limited only by the available memory of the host system. This contrasts with the faster fixed-precision arithmetic found in most ALU hardware, which typically...

     mathematical libraries. Applications include cryptography
    Cryptography
    Cryptography is the practice and study of techniques for secure communication in the presence of third parties...

    .

History

A 128-bit multicomparator was described by researchers in 1976.

A CPU with 128-bit multimedia extensions was designed by researchers in 1999.
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