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Fetching the instruction opcodes from program memory well in advance is known as prefetching and it is served by using a prefetch input queue (PIQ). The pre-fetched instructions are stored in a queue. The fetching of opcodes well in advance, prior to their need for execution, increases the overall efficiency of the processor boosting its speed ...
In computer science, instruction scheduling is a compiler optimization used to improve instruction-level parallelism, which improves performance on machines with instruction pipelines. Put more simply, it tries to do the following without changing the meaning of the code:
code which is executed but has no external effect (e.g., does not change the output produced by a program; known as dead code). A NOP instruction might be considered to be redundant code that has been explicitly inserted to pad out the instruction stream or introduce a time delay, for example to create a timing loop by "wasting time".
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 ...
The instruction cycle (also known as the fetch–decode–execute cycle, or simply the fetch–execute cycle) is the cycle that the central processing unit (CPU) follows from boot-up until the computer has shut down in order to process instructions. It is composed of three main stages: the fetch stage, the decode stage, and the execute stage.
The instruction unit (I-unit or IU), also called, e.g., instruction fetch unit (IFU), instruction issue unit (IIU), instruction sequencing unit (ISU), in a central processing unit (CPU) is responsible for organizing program instructions to be fetched from memory, and executed, in an appropriate order, and for forwarding them to an execution unit (E-unit or EU).
The average of Cycles Per Instruction in a given process (CPI) is defined by the following weighted average: := () = () Where is the number of instructions for a given instruction type , is the clock-cycles for that instruction type and = is the total instruction count.
The first machine to use out-of-order execution was the CDC 6600 (1964), designed by James E. Thornton, which uses a scoreboard to avoid conflicts. It permits an instruction to execute if its source operand (read) registers aren't to be written to by any unexecuted earlier instruction (true dependency) and the destination (write) register not be a register used by any unexecuted earlier ...