Execution unit

Part of a CPU which performs the operations instructed by the program

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In computer engineering, an execution unit (E-unit or EU) is a part of the central processing unit (CPU) or graphics processing unit (GPU) that performs the operations and calculations forwarded from the instruction unit. It may have its own internal control sequence unit (not to be confused with the CPU's main control unit), some registers, and other internal units such as an arithmetic logic unit, address generation unit, floating-point unit, load–store unit, branch execution unit^[1] or some smaller and more specific components.^[2]

It is common for modern CPUs to have multiple parallel functional units within its execution units, which is referred to as superscalar design. The simplest arrangement is to use a single bus manager unit to manage the memory interface, and the others to perform calculations. Additionally, modern CPUs' execution units are usually pipelined.

References

^ Kanter, David (November 13, 2012). "Intel's Haswell CPU Microarchitecture". Real World Tech.
^ "Execution Unit" discussion from the University of Massachusetts Amherst, archived on the Wayback Machine

Processor technologies

Models

Abstract machine
Stored-program computer
Finite-state machine
- with datapath
- Hierarchical
- Deterministic finite automaton
- Queue automaton
- Cellular automaton
- Quantum cellular automaton
Turing machine
Belt machine
Stack machine
Register machines

Architecture

Instruction set
architectures

Types	Orthogonal instruction set CISC RISC Application-specific EDGE TRIPS VLIW EPIC MISC OISC NISC ZISC VISC architecture Quantum computing Comparison Addressing modes
Instruction sets	Motorola 68000 series VAX PDP-11 x86 ARM Stanford MIPS MIPS MIPS-X Power POWER PowerPC Power ISA Clipper architecture SPARC SuperH DEC Alpha ETRAX CRIS M32R Unicore Itanium OpenRISC RISC-V MicroBlaze LMC System/3x0 S/360 S/370 S/390 z/Architecture Tilera ISA VISC architecture Epiphany architecture Others

Execution

Instruction pipelining	Pipeline stall Operand forwarding Classic RISC pipeline
Hazards	Data dependency Structural Control False sharing
Out-of-order	Scoreboarding Tomasulo's algorithm Reservation station Re-order buffer Register renaming Wide-issue
Speculative	Branch prediction Memory dependence prediction

Parallelism

Level	Bit Bit-serial Word Instruction Pipelining Scalar Superscalar Task Thread Process Data Vector Memory Distributed
Multithreading	Temporal Simultaneous Hyperthreading Simultaneous and heterogenous Speculative Preemptive Cooperative
Flynn's taxonomy	SISD SIMD Array processing (SIMT) Pipelined processing Associative processing SWAR MISD MIMD SPMD

Processor
performance

Transistor count
Instructions per cycle (IPC)
- Cycles per instruction (CPI)
Instructions per second (IPS)
Floating-point operations per second (FLOPS)
Transactions per second (TPS)
Synaptic updates per second (SUPS)
Performance per watt (PPW)
Cache performance metrics
Computer performance by orders of magnitude

Types

By application	Embedded system Microprocessor Microcontroller Mobile Ultra-low-voltage ASIP Soft microprocessor
Systems on chip	System on a chip (SoC) Multiprocessor (MPSoC) Cypress PSoC Network on a chip (NoC)
Hardware accelerators	Coprocessor AI accelerator Graphics processing unit (GPU) Image processor Vision processing unit (VPU) Physics processing unit (PPU) Digital signal processor (DSP) Tensor Processing Unit (TPU) Secure cryptoprocessor Network processor Baseband processor

Word size

Core count

Components

Functional units	Arithmetic logic unit (ALU) Address generation unit (AGU) Floating-point unit (FPU) Memory management unit (MMU) Load–store unit Translation lookaside buffer (TLB) Branch predictor Branch target predictor Integrated memory controller (IMC) Memory management unit Instruction decoder
Logic	Combinational Sequential Glue Logic gate Quantum Array
Registers	Processor register Status register Stack register Register file Memory buffer Memory address register Program counter
Control unit	Hardwired control unit Instruction unit Data buffer Write buffer Microcode ROM Counter
Datapath	Multiplexer Demultiplexer Adder Multiplier CPU Binary decoder Address decoder Sum-addressed decoder Barrel shifter
Circuitry	Integrated circuit 3D Mixed-signal Power management Boolean Digital Analog Quantum Switch

Power
management

Basic computer components

Input devices

Pointing devices	Graphics tablet Game controller Light pen Mouse Optical Optical trackpad Pointing stick Touchpad Touchscreen Trackball
Other	Keyboard Image scanner Graphics card GPU Microphone Refreshable braille display Sound card Sound chip Webcam Softcam

Output devices

Removable
data storage

Computer case

Central processing unit
- Microprocessor
Motherboard
Memory
- RAM
- BIOS
Data storage
- HDD
- SSD (SATA / NVMe)
- SSHD
Power supply
- SMPS
MOSFET
- Power MOSFET
- VRM
Network interface controller
Fax modem
Expansion card

Ports

Current	Ethernet USB Thunderbolt Analog audio jack DisplayPort HDMI
Obsolete	FireWire (IEEE 1394) Parallel port Serial port Game port PS/2 port eSATA DVI VGA