Single-core

A single-core processor is a microprocessor with a single core on a chip, running a single thread at any one time. The term became common after the emergence of multi-core processors (which have several independent processors on a single chip) to distinguish non-multi-core designs. For example, Intel released a Core 2 Solo and Core 2 Duo, and one would refer to the former as the 'single-core' variant. Most microprocessors prior to the multi-core era are single-core. The class of many-core processors follows on from multi-core, in a progression showing increasing parallelism over time.

Processors remained single-core until it was impossible to achieve performance gains from the increased clock speed and transistor count allowed by Moore's law (there were diminishing returns to increasing the depth of a pipeline, increasing CPU cache sizes, or adding execution units).^[1]

Increasing parallel trend

Single-core - one processor on a die.
Multi-core - a 'few' processors on a die,e.g. 2,4,8. As of 2016, most CPUs fall into this category.
Many-core - a 'large number' of processors on a die, e.g. 10s, 100s, 1000's. Some specialist ASICs/Accelerators and GPUs fall into this category.

References

↑ "architecting solutions of the manycore era".

CPU technologies

Architecture	Von Neumann Harvard (Modified) Dataflow TTA

Instruction set	ASIP CISC RISC EDGE (TRIPS) VLIW (EPIC) MISC OISC NISC ZISC Comparison

Word size	1-bit 4-bit 8-bit 9-bit 10-bit 12-bit 15-bit 16-bit 18-bit 22-bit 24-bit 25-bit 26-bit 27-bit 31-bit 32-bit 33-bit 34-bit 36-bit 39-bit 40-bit 48-bit 50-bit 60-bit 64-bit 128-bit 256-bit 512-bit Variable

Execution	Instruction pipelining Bubble Operand forwarding Out-of-order execution Register renaming Speculative execution Branch predictor Memory dependence prediction Hazards

Parallel level	Bit Bit-serial Word Instruction Scalar Superscalar Task Thread Process Data Vector Memory

Multithreading	Temporal Simultaneous Preemptive Cooperative

Flynn's taxonomy	SISD SIMD MISD MIMD SPMD Addressing mode

Core count	Single-core processor Multi-core processor Manycore processor

Types	Digital signal processor (DSP) GPGPU Microcontroller Physics processing unit System on a chip (SoC) Cellular

Components	Address generation unit (AGU) Arithmetic logic unit (ALU) Barrel shifter Floating-point unit (FPU) Back-side bus Multiplexer Demultiplexer Registers Memory management unit (MMU) Translation lookaside buffer (TLB) Cache Register file Microcode Control unit Clock rate

Power management	APM ACPI Dynamic frequency scaling Dynamic voltage scaling Clock gating

Hardware security	Non-executable memory (NX bit) Bounds checking (Intel MPX) Hardware restriction (firmware) Software Guard Extensions (Intel SGX) Trusted Execution Technology Secure cryptoprocessor Hardware security module Hengzhi chip

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