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In computer engineering, instruction pipelining is a technique for implementing instruction-level parallelism within a single processor. Pipelining attempts to keep every part of the processor busy with some instruction by dividing incoming instructions into a series of sequential steps (the eponymous "pipeline") performed by different processor units with different parts of instructions ...
This process is much faster than sending out an address, reading the opcode and then decoding and executing it. Fetching the next instruction while the current instruction is being decoded or executed is called pipelining. [8] The 8086 processor has a six-byte prefetch instruction pipeline, while the 8088 has a four-byte prefetch. As the ...
The 8086 [3] (also called iAPX 86) [4] is a 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, [5] is a slightly modified chip with an external 8-bit data bus (allowing the use of cheaper and fewer supporting ICs), [note 1] and is notable as the processor used in the original IBM PC design.
Instruction pipelining, where the execution of multiple instructions can be partially overlapped. Superscalar execution, VLIW , and the closely related explicitly parallel instruction computing concepts, in which multiple execution units are used to execute multiple instructions in parallel.
An instruction set architecture (ISA) is an abstract model of a computer, also referred to as computer architecture.A realization of an ISA is called an implementation.An ISA permits multiple implementations that may vary in performance, physical size, and monetary cost (among other things); because the ISA serves as the interface between software and hardware.
Seymour Cray's CDC 6600 from 1964 is often mentioned as the first superscalar design. The 1967 IBM System/360 Model 91 was another superscalar mainframe. The Intel i960CA (1989), [3] the AMD 29000-series 29050 (1990), and the Motorola MC88110 (1991), [4] microprocessors were the first commercial single-chip superscalar microprocessors.
In simpler CPUs, the instruction cycle is executed sequentially, each instruction being processed before the next one is started. In most modern CPUs, the instruction cycles are instead executed concurrently, and often in parallel, through an instruction pipeline: the next instruction starts being processed before the previous instruction has finished, which is possible because the cycle is ...
For example, many implementations of the instruction pipeline only allow a single memory load or memory store per instruction, leading to a load–store architecture (RISC). For another example, some early ways of implementing the instruction pipeline led to a delay slot.