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The instruction prefetch queue speeds up the processing of microprocessors by attempting to have the next opcode bytes available to the execution unit before it actually needs them. This works because, statistically, there is time spent by the execution unit in executing a particular instruction; time that the bus interface unit can use to go ahead and prefetch the next opcode bytes. Sometimes, this results in a loss of time, because the execution unit may branch to some other location. Modern processors attempt to sidestep that by using branch prediction algorithms.
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Describe the functions of the 8086 queue?
The 8086/8088 instruction queue is a buffer that holds opcode bytes that have been prefetched by the bus interface unit. This speeds up operations of the processor by helping to reduce fetch latency, i.e. to improve the probability that an opcode byte fetched by the processor is already available.
What is an instruction queue in 8086?
The 8086/8088 instruction queue is a buffer that holds opcode bytes that have been prefetched by the bus interface unit. This speed up operations of the processor by helping to reduce fetches latency, i.e. to improve the probability that an opcode byte fetched by the processor is already available. This works best when there is no branching, as a branch would invalidate the queue. Advanced processors attempt to "predict" the branch, making the probability even better.
Why is size of instruction queue of 8086 fixed to 6 bytes?
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.
Why pipelining used in 8086?
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.
What is prefetch queue in 8086?
To speed up the program execution, the B.I.U fetches six instructions byte ahead of time from memory and stores in FIFO registers called "queue". Since EU and B.I.U are independent, the B.I.U fetches additional instruction, while EU decodes and executes a previously fetched instruction. When the execution unit is ready for its next instruction, it simply reads the instruction from the queue. The main point here is that, fetching of the next instruction is overlapped with the execution of current instruction. This is called pipe lining pipe lining saves time required for executing instructions. For example, if a multiplication operation is to be performed with its operands and registers, the microprocessor takes 100 clock-cycles, however, without pipe lining and with pipe lining, the number of clock cycles required to multiply two operands get relatively reduced. There are many instructions in 8086 microprocessor that require huge number of clock cycles. Thus, the prefetch queue becomes a circular part in enhancing the performance of the system.
What is instruction prefetching?
Instruction pre-fetching is very important phenomena in 8086 microprocessor. There is a 16-bit register set located in the BIU (bus Interface Unit) known as QUEUE.While EU (Execution Unit) is working on the instructions i.e decoding and executing them, queue fetches the next sixinstruction byte of the running program. It is to be noted that, unlike stack (which is last in first out), queue is first in first out. Instruction which is fetched first is retrieved first.This is much faster than sending out the address and waiting for memory to send back the instruction byte or bytes.Limitation of QUEUE:This pre-fetching of instruction speeds up processing but sometimes during 1JMP and CALL statements, queue has to be dumped and reloaded again starting from the next address.Fetching the instruction while the current instruction executes is called pipelining.1. Like in c++ programming, when a function is called the control is transferred to the function and its instruction
What is queue explain the basic element of queue?
The queue is a linear data structure where operations of insertion and deletion are performed at separate ends also known as front and rear. Queue is a FIFO structure that is first in first out. Following are the types of queue: Linear queue Circular queue Priority queue Double ended queue ( or deque )
How do you spell que up?
The word "queue" means a waiting line. To queue up is to wait in line. (pronounced like the letter Q)
What does la queue mean in French?
la queue is either an animal's tail, or the file of people queuing up.
What is the correct spelling of que?
The correct spelling for people lining up for something is a queue. or cue for pool.
What does une queue mean in English?
Une queue (fem.) is either a file of people queueing up, or the tail of an animal.
What are the fastest mammals?
# The cheetah, which can reach speeds up to 65mph. # The pronghorn antelope, speeds up to 53mph. # The Mongolian gazelle, speeds up to 50mph. # The Springbok, speeds up to 50mph. # Grant's Gazelle, speeds up to 47mph. # Thomson's Gazelle, speeds up to 47mph. # The European hare, with speeds up to 43mph.
