256-bit computing

In computer architecture, 256-bit integers, memory addresses, or other data units are those that are 256 bits (32 octets) wide. Also, 256-bit central processing unit (CPU) and arithmetic logic unit (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 256-bit integers or addresses, though a number of processors do operate on 256-bit data. As of 2012, CPUs feature SIMD instruction sets (Advanced Vector Extensions and the planned FMA instruction set etc.) where 256-bit vector registers are used to store several smaller numbers, such as eight 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 256 binary digits in length, only their registers have the size of 256-bits.

Uses

• 256 bits is a common key size for symmetric ciphers in cryptography, such as Advanced Encryption Standard
• 256-bit processors could be used for addressing directly up to 2²⁵⁶ bytes. Already 2¹²⁸ (128-bit) would greatly exceed the total data stored on Earth as of 2010, which has been estimated to be around 1.2 zettabytes (over 2⁷⁰ bytes)
• The Efficeon processor was Transmeta's second-generation 256-bit VLIW design which employed a software engine to convert code written for x86 processors to the native instruction set of the chip
• Increasing the word size can speed up multiple precision mathematical libraries. Applications include cryptography

History

• The Data-Intensive Architecture (DIVA) system incorporated processor-in-memory (PIM) 5-stage pipelined 256-bit datapath, complete with register file and ALU blocks in a "WideWord" processor

See also

• Berkeley IRAM project
• Computational RAM