Slot (computer architecture)
Encyclopedia
A slot comprises the operation issue and data paths machinery surrounding a collection of one or more functional units (FUs) which share these resources. The term slot is common for this purpose in the VLIW
world where the relationship between operation in an instruction and pipeline to execute it is explicit. In dynamically scheduled machines the concept is more commonly called an execute pipeline.
Modern conventional CPU
s have several compute pipelines (say two ALU
, one FPU
, one SSE
/MMX, one branch
) each of which can issue one instruction per basic cycle
but can have several in flight. These are what correspond to slots. The pipelines may have several FUs - an adder
and a multiplier, say - but only one FU in a pipeline can be issued to in a particular cycle. The FU population of a pipeline/slot is a design option in a CPU.
Very long instruction word
Very long instruction word or VLIW refers to a CPU architecture designed to take advantage of instruction level parallelism . A processor that executes every instruction one after the other may use processor resources inefficiently, potentially leading to poor performance...
world where the relationship between operation in an instruction and pipeline to execute it is explicit. In dynamically scheduled machines the concept is more commonly called an execute pipeline.
Modern conventional CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
s have several compute pipelines (say two ALU
Arithmetic logic unit
In computing, an arithmetic logic unit is a digital circuit that performs arithmetic and logical operations.The ALU is a fundamental building block of the central processing unit of a computer, and even the simplest microprocessors contain one for purposes such as maintaining timers...
, one FPU
Floating point unit
A floating-point unit is a part of a computer system specially designed to carry out operations on floating point numbers. Typical operations are addition, subtraction, multiplication, division, and square root...
, one SSE
Streaming SIMD Extensions
In computing, Streaming SIMD Extensions is a SIMD instruction set extension to the x86 architecture, designed by Intel and introduced in 1999 in their Pentium III series processors as a reply to AMD's 3DNow! . SSE contains 70 new instructions, most of which work on single precision floating point...
/MMX, one branch
Branch (computer science)
A branch is sequence of code in a computer program which is conditionally executed depending on whether the flow of control is altered or not . The term can be used when referring to programs in high level languages as well as program written in machine code or assembly language...
) each of which can issue one instruction per basic cycle
Instruction cycle
An instruction cycle is the basic operation cycle of a computer. It is the process by which a computer retrieves a program instruction from its memory, determines what actions the instruction requires, and carries out those actions...
but can have several in flight. These are what correspond to slots. The pipelines may have several FUs - an adder
Adder (electronics)
In electronics, an adder or summer is a digital circuit that performs addition of numbers.In many computers and other kinds of processors, adders are used not only in the arithmetic logic unit, but also in other parts of the processor, where they are used to calculate addresses, table indices, and...
and a multiplier, say - but only one FU in a pipeline can be issued to in a particular cycle. The FU population of a pipeline/slot is a design option in a CPU.