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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.
The 8086 processor has a six-byte prefetch instruction pipeline, while the 8088 has a four-byte prefetch. As the Execution Unit is executing the current instruction, the bus interface unit reads up to six (or four) bytes of opcodes in advance from the memory. The queue lengths were chosen based on simulation studies. [9]
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 ...
ILP must not be confused with concurrency.In ILP, there is a single specific thread of execution of a process.On the other hand, concurrency involves the assignment of multiple threads to a CPU's core in a strict alternation, or in true parallelism if there are enough CPU cores, ideally one core for each runnable thread.
An 8086 system, including coprocessors such as 8087 and 8089, and simpler Intel-specific system chips, [d] was thereby described as an iAPX 86 system. [7] [e] There were also terms iRMX (for operating systems), iSBC (for single-board computers), and iSBX (for multimodule boards based on the 8086-architecture), all together under the heading ...
Very long pipeline. The Prescott was a major architectural revision. Later revisions were the first to feature Intel's x86-64 architecture, enhanced branch prediction and trace cache, and eventually support was added for the NX (No eXecute) bit to implement executable-space protection.
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 ...
The pipelined architecture allows multiple instructions to overlap in execution, much like an assembly line. The pipeline includes several different stages which are fundamental in microarchitecture designs. [5] Some of these stages include instruction fetch, instruction decode, execute, and write back.