increases speed
6 bytes
6 bytes
In 8086 the instruction queue is 6 byte long. This is because even the longest 8086 instruction is 6 byte long. Thus it is possible to prefetch even the longest instruction in the instruction set.
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An instruction queue is used in the 8086 to speed up the average time it takes to process an instruction. Some instructions are faster than the bus, while some are slower. If the CPU had to wait for all of the instructions, there would be gaps of time where the CPU is doing nothing. The queue helps to eliminate that gap by prefetching instructions in the hope that they will be ready for use when the CPU gets to them.
Because that's how Intel designed it. They chose a 6 byte queue in the 8086 in order to optimize speed versus latency of the execution unit versus the bus interface unit. The decision for 6 bytes, as compared to 4 or 8 or some other number was a cost tradeoff and a recognition of the average mix of instruction execution cycle times in a typical processing thread.
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8086 is a pipelined processor. In 8086 to speed up the execution of a program,instruction fetching and executing the instruction are overlapped each other.This is a part of pipelined technique.
The bus interface unit provides the func- tions related to instruction fetching and queuing, op- erand fetch and store, and address relocation. This unit also provides the basic bus control. The overlap of instruction pre-fetching provided by this unit serves to increase processor performance through improved bus bandwidth utilization. Up to 6 bytes of the instruction stream can be queued while waiting for decoding and execution.
in 8086, there is instruction queue of 6 byte. It is one of the reason behind giving name. 8086 was introducing pipeline architecture.
queue of 8086 microprocessor is 6 bits
6-bytes