A slot comprises the operation issue and data path machinery surrounding a set of one or more

execution unit In computer engineering, an execution unit (E-unit or EU) is a part of the central processing unit (CPU) that performs the operations and calculations as instructed by the computer program. It may have its own internal control sequence unit (not ...

(also called a functional unit (FU)) which share these resources. The term slot is common for this purpose in

very long instruction word Very long instruction word (VLIW) refers to instruction set architectures designed to exploit instruction level parallelism (ILP). Whereas conventional central processing units (CPU, processor) mostly allow programs to specify instructions to exe ...

(VLIW) computers, where the relationship between operation in an instruction and

pipeline Pipeline may refer to: Electronics, computers and computing * Pipeline (computing), a chain of data-processing stages or a CPU optimization found on ** Instruction pipelining, a technique for implementing instruction-level parallelism within a s ...

to execute it is explicit. In dynamically scheduled machines, the concept is more commonly called an ''execute pipeline''. Modern conventional

central processing unit A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, an ...

s (CPU) have several compute pipelines, for example: two

arithmetic logic unit In computing, an arithmetic logic unit (ALU) is a combinational digital circuit that performs arithmetic and bitwise operations on integer binary numbers. This is in contrast to a floating-point unit (FPU), which operates on floating point numb ...

s (ALU), one

floating point unit Floating may refer to: * a type of dental work performed on horse teeth * use of an isolation tank * the guitar-playing technique where chords are sustained rather than scratched * ''Floating'' (play), by Hugh Hughes * Floating (psychological ph ...

(FPU), one

Streaming SIMD Extensions In computing, Streaming SIMD Extensions (SSE) is a single instruction, multiple data (SIMD) instruction set extension to the x86 architecture, designed by Intel and introduced in 1999 in their Pentium III series of Central processing units (CPUs ...

(SSE) (such as MMX), one

branch A branch, sometimes called a ramus in botany, is a woody structural member connected to the central trunk of a tree (or sometimes a shrub). Large branches are known as boughs and small branches are known as twigs. The term '' twig'' usually ...

. Each of them can issue one instruction per basic

instruction cycle 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 ...

, but can have several instructions in process. These are what correspond to slots. The pipelines may have several FUs, such as an

adder Adder may refer to: * AA-12 Adder, a Russian air-to-air missile * Adder (electronics), an electronic circuit designed to do addition * Adder Technology, a manufacturing company * Armstrong Siddeley Adder, a late 1940s British turbojet engine * ''B ...

and a multiplier, but only one FU in a pipeline can be issued to in a given cycle. The FU population of a pipeline (slot) is a design option in a CPU.

References

Computer architecture {{Compu-stub