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 speed of processor is expressed in Hertz and current processors work with 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 mostly used in Mobile tablets, Smart phones, Cars, game console and all equipment fitted with embedded systems. Different Processors use different Instruction sets and it has its own pros and cons.

ARM Processors

Given below are the ARM Processors:

1. ISA

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

2. CISC

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

3. RISC

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

Features of ARM Processors:

Single cycle to execute an instruction,
Interchangeable use of Registers & Address mode 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 processor.
It processes reduced number of instructions, at a higher speed, completing multi millions of instructions per second (MIPS). Term “Reduced” indicates the work content in an instruction is reduced and it is made simple when 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 easier programming and reduce coding efforts.

Applications of ARM Processors:

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

ARM Architecture Acorn

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

1. ARM2

With help of VLSI who provided ROM support, Acorn develop ARM2. Low latency was achieved along with efficiency of 6502. ARM2 has 32bit size in which 26 bits were for address and 6 bits for registers. It had only 30,000 transistors as against 40,000 mark of Motorola. This had helped in achieving low power consumption, heat dissipation, better performance and take a lead over intel 80286. ARM3 was later released with a provision to hold cache memory to improve the 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 by 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 the mobile phones had ARM processor. ARM6 continued to be used in mobile devices and its market share in 2013 was 60%.

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ARM designed ARM7, ARM8 incorporating many improvements over ARM6. ARMv5 to ARMv7 was used in mobile devices, phones and PDAs. Due to its unique features ARM processors was deployed in embedded system to be fitted on equipment. ARMv8 is used in high-end gadgets currently.

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 own processor using ARM core and other products to build their own CPU, Microcontrollers, System-on-chips and devices and can sell it to other original equipment manufacturers. It sells only Core to the third party vendors who wish to develop their own chip design using ARM core. Arm holding does not allow reselling of it licenses. It sells IP only for the value perceived and delivered to its customers

List of ARM Architecture

Given below table shows few of the various architecture developed by ARM as well as their third party vendors.

Architecture	Core (bits)	ARM Core	Third party
ARMv1	32	ARM1
ARMv2	32	ARM2, ARM3, ARM250	Amber, STORM open soft core
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 of ARM

Given below are the advantages and disadvantages:

Advantages

Below are the advantages:

Consumes less power and generate less heat.
Economical when compared to others.
Works faster.
Requires less hardware and hence ideal for mini gadgets.
Number one choice by end users due to better support infrastructure and easy availability.

Disadvantages

Below are the disadvantages:

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

Conclusion

ARM processors is used extensively in Mobile devices, PDA, Phones, Microsoft Surface etc. It also provides Power efficient solutions in servers and super computers.