Editing Barrel processor (section)

{{short description|CPU that switches between threads of execution on every cycle}}
A '''barrel processor''' is a [[Central processing unit|CPU]] that switches between [[Thread (computer science)|threads]] of execution on every [[Instruction cycle|cycle]]. This [[CPU design]] technique is also known as "interleaved" or "fine-grained" [[temporal multithreading]]. Unlike [[simultaneous multithreading]] in modern [[superscalar]] architectures, it generally does not allow execution of multiple instructions in one cycle.

Like [[preemptive multitasking]], each thread of execution is assigned its own [[program counter]] and other [[hardware register]]s (each thread's [[architectural state]]). A barrel processor can guarantee that each thread will execute one instruction every ''n'' cycles, unlike a [[preemptive multitasking]] machine, that typically runs one thread of execution for tens of millions of cycles, while all other threads wait their turn.

A technique called [[C-slowing]] can automatically generate a corresponding barrel processor design from a single-tasking processor design.  An ''n''-way barrel processor generated this way acts much like ''n'' separate [[multiprocessing]] copies of the original single-tasking processor, each one running at roughly 1/''n'' the original speed.{{Citation needed|reason=Couldn't find info on this. May be original research?|date=October 2019}}