Editing Instruction set architecture (section)

===Complex instructions===
Processors may include "complex" instructions in their instruction set. A single "complex" instruction does something that may take many instructions on other computers. Such instructions are [[typified]] by instructions that take multiple steps, control multiple functional units, or otherwise appear on a larger scale than the bulk of simple instructions implemented by the given processor. Some examples of "complex" instructions include:

*transferring multiple registers to or from memory (especially the [[Call stack|stack]]) at once
*moving large blocks of memory (e.g. [[string copy]] or [[DMA transfer]])
*complicated integer and [[floating-point arithmetic]] (e.g. [[square root]], or [[transcendental function]]s such as [[logarithm]], [[sine]], [[cosine]], etc.)
*''{{vanchor|[[Single instruction, multiple data|SIMD]] instruction|SIMD instruction}}s'', a single instruction performing an operation on many homogeneous values in parallel, possibly in dedicated [[SIMD register]]s
*performing an atomic [[test-and-set]] instruction or other [[read–modify–write]] [[atomic instruction]]
*instructions that perform [[arithmetic logic unit|ALU]] operations with an operand from memory rather than a register

Complex instructions are more common in CISC instruction sets than in RISC instruction sets, but RISC instruction sets may include them as well. RISC instruction sets generally do not include ALU operations with memory operands, or instructions to move large blocks of memory, but most RISC instruction sets include [[Single instruction, multiple data|SIMD]] or [[vector processing|vector]] instructions that perform the same arithmetic operation on multiple pieces of data at the same time. SIMD instructions have the ability of manipulating large vectors and matrices in minimal time. SIMD instructions allow easy [[parallelization]] of algorithms commonly involved in sound, image, and video processing. Various SIMD implementations have been brought to market under trade names such as [[MMX (instruction set)|MMX]], [[3DNow!]], and [[AltiVec]].

{{Anchor|Parts of an instruction}}