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 a processing unit that performs the operations and calculations forwarded from the instruction unit. It may have its own internal control sequence unit (not to be confused w ...
(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 that are designed to exploit instruction-level parallelism (ILP). A VLIW processor allows programs to explicitly specify instructions to execute in parallel, whereas conve ...
(VLIW) computers, where the relationship between operation in an
instruction and
pipeline
A pipeline is a system of Pipe (fluid conveyance), pipes for long-distance transportation of a liquid or gas, typically to a market area for consumption. The latest data from 2014 gives a total of slightly less than of pipeline in 120 countries ...
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 primary Processor (computing), processor in a given computer. Its electronic circuitry executes Instruction (computing), instructions ...
s (CPU) have several compute pipelines, for example: two
arithmetic logic unit
In computing, an arithmetic logic unit (ALU) is a Combinational logic, 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 ...
s (ALU), one
floating point unit
A floating-point unit (FPU), numeric processing unit (NPU), colloquially math coprocessor, is a part of a computer system specially designed to carry out operations on floating-point numbers. Typical operations are addition, subtraction, multipli ...
(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 its Pentium III series of central processing units (CPU ...
(SSE) (such as
MMX), one
branch
A branch, also called a ramus in botany, is a stem that grows off from another stem, or when structures like veins in leaves are divided into smaller veins.
History and etymology
In Old English, there are numerous words for branch, includ ...
. 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 and a
multiplier Multiplier may refer to:
Mathematics
* Multiplier (arithmetic), the number of multiples being computed in multiplication
* Constant multiplier, a constant factor with units of measurement
* Lagrange multiplier, a scalar variable used in mathema ...
, 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
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