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In a computer instruction set architecture (ISA), an execute instruction is a machine language instruction which treats data as a machine instruction and executes it. It can be considered a fourth mode of instruction sequencing after ordinary sequential execution , branching , and interrupting . [ 1 ]
[a] Branch (or branching, branched) may also refer to the act of switching execution to a different instruction sequence as a result of executing a branch instruction. Branch instructions are used to implement control flow in program loops and conditionals (i.e., executing a particular sequence of instructions only if certain conditions are ...
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 ...
Executing a set of statements zero or more times, until some condition is met (i.e., loop - the same as conditional branch) Executing a set of distant statements, after which the flow of control usually returns (subroutines, coroutines, and continuations) Stopping the program, preventing any further execution (unconditional halt)
Since the branch itself will generally not be the last instruction in an aligned group, instructions after the taken branch (or its delay slot) will be discarded. Once again, assuming a uniform distribution of branch instruction placements, 0.5, 1.5, and 3.5 instructions fetched are discarded.
For example, a conditional branch instruction will transfer control if the condition is true, so that execution proceeds to a different part of the program, and not transfer control if the condition is false, so that execution continues sequentially.
If the branch is not taken, the pipeline stays full. If the branch is taken, the instruction is flushed (marked as if it were a NOP), and one cycle's opportunity to finish an instruction is lost. Branch Likely: Always fetch the instruction after the branch from the instruction cache, but only execute it if the branch was taken.
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.