ARM microarchitectures

ARM microarchitectures
Name	ARM microarchitectures
Designer	ARM Holdings
Bits	32-bit, 64-bit
Introduced	1985
Version	ARMv9
Design	RISC
Endianness	Bi (little as default)
Page size	4 KB, 16 KB, 64 KB
Extensions	NEON (SIMD), TrustZone, SVE
Predecessor	Acorn Computers

ARM microarchitectures. The family of central processing unit cores implementing the ARM architecture instruction set, designed primarily by ARM Holdings and its architectural licensees. These designs prioritize energy efficiency and performance per watt, making them dominant in mobile devices, embedded systems, and increasingly in high-performance computing. The evolution from simple Acorn Computers prototypes to sophisticated multicore designs has been driven by partnerships with major semiconductor companies like Apple Inc., Qualcomm, and Samsung Electronics.

Overview

ARM microarchitectures are the physical implementations of the ARM architecture, a reduced instruction set computer family originally developed at Acorn Computers in the 1980s. The intellectual property is licensed by ARM Holdings, now a subsidiary of SoftBank Group, to numerous partners who fabricate the system on a chip designs. These cores power an immense range of products, from Internet of things sensors to the Fugaku (supercomputer), the world's fastest supercomputer in 2020. The business model of licensing semiconductor intellectual property cores, rather than manufacturing chips, has been fundamental to the global ecosystem surrounding these designs.

Design philosophy

The foundational philosophy emphasizes simplicity, low power consumption, and high code density, principles inherited from the early Berkeley RISC project and the original Acorn RISC Machine. This is achieved through a consistent load/store architecture, a large uniform register file, and a focus on efficient pipeline (computing) design. Key innovations like the Thumb instruction set enhance code density for embedded systems, while the big.LITTLE heterogeneous processing technology, pioneered by ARM Holdings, optimizes for both performance and battery life. This philosophy has made the architecture exceptionally successful in markets dominated by mobile phones and tablet computers.

Evolution and generations

The evolution began with the ARM1, designed by Sophie Wilson and Steve Furber for the BBC Micro computer. Early generations, up to the ARM7 and ARM9 families, established dominance in mobile phones like the Nokia 6110. The introduction of the Cortex-A8 marked the shift to modern application processors, enabling devices like the original iPhone. Subsequent cores like the Cortex-A57 brought 64-bit support via the ARMv8-A architecture. Recent generations, such as the Cortex-X2 and Cortex-A710, implement the ARMv9-A architecture with features like the Scalable Vector Extension for advanced high-performance computing workloads.

Key architectural features

A defining feature is the consistent use of a load/store architecture with a fixed-length instruction set, simplifying pipeline (computing) design. Most implementations include the Thumb instruction set for improved code density and the Jazelle extension for accelerated Java (programming language) execution. Security is provided by TrustZone technology, creating a secure enclave within the processor. For multimedia and scientific computing, the NEON (SIMD) advanced SIMD engine and the newer Scalable Vector Extension are critical. The big.LITTLE processing scheme and DynamIQ technology allow for flexible heterogeneous computing configurations.

Implementations and products

Licensed implementations range from small Cortex-M series cores for microcontrollers to high-performance Cortex-A and custom designs. Apple Inc. designs its Apple silicon chips, like the Apple A15 and Apple M1, which power the iPhone and MacBook. Qualcomm creates the Snapdragon series, used in many Android (operating system) smartphones from Samsung Electronics and others. Nvidia employs ARM designs in its Tegra and Grace processors for automotive and data center markets. Other notable implementations include Amazon Web Services Graviton instances and Ampere Computing's Altra server CPUs.

Comparison with other architectures

Compared to the dominant x86 architectures from Intel and Advanced Micro Devices, ARM designs typically offer superior energy efficiency, making them prevalent in battery (electricity)-constrained environments. The RISC foundation contrasts with the complex instruction set computer heritage of x86, though modern implementations of both have converged in many aspects. Against other RISC architectures like Power ISA from IBM or RISC-V, the ARM ecosystem benefits from a mature, pervasive software ecosystem including Android (operating system), iOS, and widespread Linux kernel support. In supercomputer rankings like the TOP500, ARM-based systems like Fugaku (supercomputer) compete directly with those based on x86 and SPARC architectures.

Category:ARM microarchitecture Category:Microprocessors Category:Computer architecture