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This led to the term "Meaningless Indicator of Processor Speed," [5] or less commonly, "Meaningless Indices of Performance," [6] being popular amongst technical people by the mid-1980s. For this reason, MIPS has become not a measure of instruction execution speed, but task performance speed compared to a reference.
While early generations of CPUs carried out all the steps to execute an instruction sequentially, modern CPUs can do many things in parallel. As it is impossible to just keep doubling the speed of the clock, instruction pipelining and superscalar processor design have evolved so CPUs can use a variety of execution units in parallel - looking ahead through the incoming instructions in order to ...
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 ...
For example, with six executions units, six new instructions are fetched in stage 1 only after the six previous instructions finish at stage 5, therefore on average the number of clock cycles it takes to execute an instruction is 5/6 (CPI = 5/6 < 1). To get better CPI values with pipelining, there must be at least two execution units.
v is the execution speed of the task; T is the execution time of the task; W is the execution workload of the task. Throughput of an architecture is the execution rate of a task: = = =, where ρ is the execution density (e.g., the number of stages in an instruction pipeline for a pipelined architecture);
Speculative execution, which allows the execution of complete instructions or parts of instructions before being certain whether this execution should take place. A commonly used form of speculative execution is control flow speculation, where instructions past a control flow instruction (e.g., a branch) are executed before the target of the ...
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 clock rate of a CPU is limited by the time it takes to execute the slowest sub-operation of any instruction; decreasing that cycle-time often accelerates the execution of other instructions. [46] The focus on "reduced instructions" led to the resulting machine being called a "reduced instruction set computer" (RISC).