What is ARM?

Updated May 31, 2023

Introduction to ARM

CPU is the brain of a computer, and it executes instructions as per the program code/logic flow, and it is also known as Processor. The processor’s speed is expressed in Hertz, and current processors work with a clock speed of more than one Giga Herz (1,000,000,000 Cycles/second). Intel and Advanced Micro Devices (AMD) processors are used in Servers, Desktops, and Laptops. ARM, IBM, and ATI processors are primarily used in Mobile tablets, Smartphones, Cars, game consoles, and all equipment fitted with embedded systems. Different Processors use different Instruction sets, which have pros and cons.

ARM Processors

1. ISA

Processors work on different instruction sets Architecture (ISA). ISA depicts how memory is accessed, instructions are processed, and Input / Output operations are managed. Architecture defines the way of connecting all the pieces and making the processor. ISA is an effective communication medium between the Programmer and the Processor though there are many formal layers between them.

2. CISC

Two major instruction sets are Reduced Instruction Set Computing (RISC) and Complex Instruction set computing (CISC). Intel x86, AMD, Motorola, VAX, and PDP-11 Processors use CISC Architecture, whereas ARM, MIPS, PA-RISC, PIC, AVR, and Power processors use RISC architecture.

3. RISC

ARM processor belongs to the RISC family architecture, and Advanced RISC Machines developed it. CISC was the only ISA for some time, and there was no formal categorization of ISA then. When RISC was invented, Categorization was done to identify different ISAs. RISC, the latest ISA, executes one simple (reduced) instruction in about one clock cycle. Software focused on enhancing performance uses RAM to process multiple instructions and execute the instruction faster.

Features of ARM Processors

• Single-cycle to execute an instruction.
• Registers & Address mode’s interchangeable use due to its uniform instruction format (Orthogonal Instruction set).
• Consumes less power.
• Deployed in Simple and small devices.
• ARM processors are 32-bit, 64-bit multicore processors.
• It processes fewer instructions at a higher speed, completing multi-millions of instructions per second (MIPS). The term “Reduced” indicates the work content in instruction is reduced and made simple compared to CISC.
• Require more memory to execute more instructions.
• Load/Store Architecture to make hardware faster and simpler.
• Enables effective multi-core processing. Facilitates more accessible programming and reduces coding efforts.

Applications of ARM Processors

• ARM processor is deployed extensively in smartphones, tablets, mobile watches, and multimedia players.
• Miniaturized gadgets can be designed with ARM processors as the hardware (transistors) requirements are low due to the reduced instruction set.

ARM Architecture Acorn

It is an acronym for Advanced RISC Machine. Still, its original name was the Acorn RISC machine developed by Arm Holdings, and this architecture was licensed to the third-party developer to package this in their products. The first ARM product to be released was the 6502-based BBC Micro series. It did not support a graphic interface.

1. ARM2

With the help of VLSI, who provided ROM support, Acorn developed ARM2. Low latency was achieved along with an efficiency of 6502. ARM2 has a 32-bit size in which 26 bits are for addresses and 6 bits for registers. It had only 30,000 transistors as against the 40,000 marks of Motorola. This helped achieve low power consumption, heat dissipation, better performance, and take the lead over intel 80286. Later, ARM3 included a provision to hold cache memory to enhance performance.

2. ARM6

Acorn collaborated with Apple computer and VLSI technology and formed the new company ARM limited and new processor. ARM6 was released, and Apple built their Apple Newton PDA using ARM6-based ARM610. These processors were used in PCs by Acorn. DEC developed Strongarm using this processor. Intel incorporated the same processor in i960 processors. No of transistors grew only to 35000 in ARM6. In the year 2005, 98% of mobile phones had ARM processors. Mobile devices continued to utilize ARM6, which maintained a market share of 60% in 2013.

ARM designed ARM7 and ARM8, incorporating many improvements over ARM6. Mobile devices, phones, and PDAs utilized ARMv5 to ARMv7. Equipment manufacturers deployed ARM processors in embedded systems due to their unique features. Currently, high-end gadgets make use of ARMv8 architecture.

Innovative License Model

ARM holding, floated from original Acorn, sells IP Cores to third-party vendors in a variable model in terms of cost and deliverables. Third-party vendors can build their processors using ARM core and other products to build their CPU, Microcontrollers, System-on-chips, and devices. They can sell it to other original equipment manufacturers. It sells only Core to third-party vendors who wish to develop their chip design using ARM Core. Arm holding does not allow reselling of its licenses. It sells IP only for the value perceived and delivered to its customers.

List of ARM Architecture

The table below shows a few of the various architectures developed by ARM and its third-party vendors.

Architecture	Core (bits)	ARM Core	Third-party
ARMv1	32	ARM1
ARMv2	32	ARM2, ARM3, ARM250	Amber, STORM open softcore
ARMv3	32	ARM6, ARM7
ARMv4	32	ARM8	StrongARM, ZAP, FA526
ARMv4T	32	ARM7TDMi, ARM9TDMI
ARMv5TE	32	ARM7EJ, ARM9E, ARM10E	XScale, Feroceon, FA626T3
ARMv7-A	32	ARM Cortex-A5, A6, A7, A8, A9	Qualcomm Scorpion, Pj4, Apple Swift
ARMv8-A	32/64	ARM Cortex-A35, A53, A72	X-Gene, Apple, Qualcomm, Samsung

Advantages and Disadvantages

Given below are the advantages and disadvantages:

Advantages

• It consumes less power and generates less heat.
• Economical when compared to others.
• Works faster.
• Requires less hardware and is hence ideal for mini gadgets.
• Number one choice by end-users due to better support infrastructure and easy availability.

Disadvantages

• Not compatible with Windows OS.
• Speed and performance are not consistent in all cases.
• Debugging is difficult.
• Performance depends on the ability of the programmer to execute properly.

Conclusion

Mobile devices, PDAs, phones, and even Microsoft Surface heavily rely on ARM processors for their operations. It also provides Power efficient solutions for servers and supercomputers.

This is a guide to What is ARM? Here we discuss the introduction, processors, architecture acorn, list of ARM architecture, advantages, and disadvantages. You may also have a look at the following articles to learn more –

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