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In computing, a pipeline is a series of processing elements arranged in a sequence, where the output of one element is the input for the next. The concept is analogous to a factory assembly line: breaking down a complex task into smaller, specialized steps allows multiple instructions or data items to be processed concurrently, which increases overall throughput. Depending on the context, a pipeline can refer to a process at the hardware, operating system, or software level.

Hardware pipelines

Within a computer's central processing unit (CPU), a hardware pipeline, or instruction pipeline, increases performance by overlapping the execution of multiple instructions. A typical instruction can be broken down into five stages:

Instruction Fetch (IF): The instruction is read from memory.

Instruction Decode (ID): The instruction is decoded to determine the operation and operands.

Execute (EX): The operation is performed by the Arithmetic Logic Unit (ALU).

Memory Access (MEM): Data is read from or written to memory if needed.

Write Back (WB): The final result is written to a register.

Without a pipeline, the CPU would complete all five stages for one instruction before starting the next. With a pipeline, the CPU works on a different stage for a different instruction during each clock cycle. By the fifth cycle, five different instructions are being processed simultaneously, with one completing each cycle.