Bit-level parallelism is a form of

parallel computing Parallel computing is a type of computation in which many calculations or processes are carried out simultaneously. Large problems can often be divided into smaller ones, which can then be solved at the same time. There are several different f ...

based on increasing processor word size. Increasing the word size reduces the number of instructions the processor must execute in order to perform an operation on variables whose sizes are greater than the length of the word. (For example, consider a case where an

8-bit In computer architecture, 8-bit integers or other data units are those that are 8 bits wide (1 octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers or data buses ...

processor must add two

16-bit 16-bit microcomputers are microcomputers that use 16-bit microprocessors. A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two ...

integer An integer is the number zero (), a positive natural number (, , , etc.) or a negative integer with a minus sign ( −1, −2, −3, etc.). The negative numbers are the additive inverses of the corresponding positive numbers. In the languag ...

s. The processor must first add the 8 lower-order bits from each integer, then add the 8 higher-order bits, requiring two instructions to complete a single operation. A 16-bit processor would be able to complete the operation with single instruction.) Originally, all electronic computers were serial (single-bit) computers. The first electronic computer that was not a

serial computer A serial computer is a computer typified by bit-serial architecture i.e., internally operating on one bit or digit for each clock cycle. Machines with serial main storage devices such as acoustic or magnetostrictive delay lines and rotating m ...

—the first bit-parallel computer—was the 16-bit

Whirlwind A whirlwind is a weather phenomenon in which a vortex of wind (a vertically oriented rotating column of air) forms due to instabilities and turbulence created by heating and flow (current) gradients. Whirlwinds occur all over the world and i ...

from 1951. From the advent of

very-large-scale integration Very large-scale integration (VLSI) is the process of creating an integrated circuit (IC) by combining millions or billions of MOS transistors onto a single chip. VLSI began in the 1970s when MOS integrated circuit (Metal Oxide Semiconductor) ...

(VLSI) computer chip fabrication technology in the 1970s until about 1986, advancements in computer architecture were done by increasing bit-level parallelism,David E. Culler, Jaswinder Pal Singh, Anoop Gupta. Parallel Computer Architecture - A Hardware/Software Approach. Morgan Kaufmann Publishers, 1999. , pg 15 as

4-bit In computer architecture, 4-bit integers, or other data units are those that are 4 bits wide. Also, 4-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers, or data buses of that si ...

microprocessors were replaced by

, then

32-bit In computer architecture, 32-bit computing refers to computer systems with a processor, memory, and other major system components that operate on data in 32- bit units. Compared to smaller bit widths, 32-bit computers can perform large calculati ...

microprocessors. This trend generally came to an end with the introduction of 32-bit processors, which were a standard in general purpose computing for two decades. 64 bit architectures were introduced to the mainstream with the eponymous Nintendo 64 (1996), but beyond this introduction stayed uncommon until the advent of

x86-64 x86-64 (also known as x64, x86_64, AMD64, and Intel 64) is a 64-bit version of the x86 instruction set, first released in 1999. It introduced two new modes of operation, 64-bit mode and compatibility mode, along with a new 4-level paging ...

architectures around the year 2003, and 2014 for mobile devices with the ARMv8-A instruction set. On 32-bit processors, external

data bus In computer architecture, a bus (shortened form of the Latin '' omnibus'', and historically also called data highway or databus) is a communication system that transfers data between components inside a computer, or between computers. This ...

width continues to increase. For example, DDR1 SDRAM transfers 128 bits per clock cycle.

DDR2 SDRAM Double Data Rate 2 Synchronous Dynamic Random-Access Memory (DDR2 SDRAM) is a double data rate (DDR) synchronous dynamic random-access memory (SDRAM) interface. It superseded the original DDR SDRAM specification, and was itself superseded by DDR ...

transfers a minimum of 256 bits per burst.

References

{{Parallel computing Parallel computing

See also

References