ARM (Advanced RISC Machines)

Advanced RISC Machines (ARM) is a family of reduced instruction set computing (RISC) architectures developed by ARM Holdings, a subsidiary of SoftBank Group. ARM processors are widely used in embedded systems, smartphones, tablets, smartwatches, digital TVs, and other devices. In this article, we will explain the basics of ARM, its history, features, architecture, instruction set, and applications.

History

The roots of ARM go back to the 1980s when Acorn Computers, a British company, developed a new computer called the Archimedes. The Archimedes used a new processor, the ARM1, designed by Sophie Wilson and Steve Furber. The ARM1 was a 32-bit RISC processor with a clock speed of 4 MHz. It was a simple and efficient processor, and it outperformed many other processors of the time.

In 1990, ARM Holdings was formed as a joint venture between Acorn, Apple, and VLSI Technology to license and develop ARM processors. The first ARM processor designed by ARM Holdings was the ARM2, which was used in the Acorn Archimedes A5000 computer. The ARM2 was a 32-bit processor with a clock speed of 8 MHz.

In the 1990s, ARM Holdings started licensing ARM processors to other companies. The first company to license ARM processors was Cirrus Logic, which used the ARM6 processor in its PC-on-a-chip design. Over the years, ARM Holdings has licensed ARM processors to many other companies, including Qualcomm, Samsung, Apple, and Texas Instruments.

Today, ARM Holdings is one of the leading semiconductor intellectual property (IP) providers in the world, with over 130 billion ARM-based chips shipped to date.

Features

ARM processors have several features that make them popular in many devices. Some of the key features of ARM processors are:

Power Efficiency

ARM processors are designed to be power-efficient. They consume less power than many other processors, which makes them ideal for mobile devices, where battery life is critical. ARM processors achieve this efficiency by using a RISC architecture, which reduces the number of instructions needed to perform a task.

Scalability

ARM processors are highly scalable, which means that they can be used in a wide range of devices, from low-power embedded systems to high-performance servers. ARM processors can be configured with different numbers of cores, clock speeds, cache sizes, and other parameters, depending on the needs of the device.

Flexibility

ARM processors are flexible and can be customized to meet the specific needs of a device. ARM Holdings provides a range of pre-designed cores that can be licensed and integrated into a device, or a company can work with ARM to design a custom core that meets their specific requirements.

Architecture

ARM processors use a RISC architecture, which stands for Reduced Instruction Set Computing. RISC is an approach to computer design that emphasizes simple instructions that can be executed quickly. The idea is that a processor that can execute a small number of simple instructions quickly can outperform a processor that executes a large number of complex instructions slowly.

The ARM architecture is based on a load/store architecture, which means that instructions can only operate on data in registers. Memory operations are performed separately using load and store instructions. This approach simplifies the instruction set and reduces the number of instructions needed to perform a task.

Instruction Set

The ARM instruction set is designed to be compact and efficient. Instructions are fixed-length, 32 bits long, and execute in a single cycle. The ARM instruction set includes a wide range of instructions, including arithmetic, logical, and memory operations. The ARM instruction set is divided into three categories: data processing instructions, load/store instructions, and branch instructions.

Registers

ARM processors have 16 general-purpose registers, labeled R0 through R15, as well as several other registers for specific purposes. The general-purpose registers are used to store data and addresses during program execution. The other registers are used for special purposes, such as the program counter (PC), which holds the address of the current instruction, and the status register (CPSR), which holds the current processor status, such as whether the previous instruction caused an overflow.

Modes

ARM processors support several modes of operation, which allow the processor to switch between different operating modes depending on the current task. The most common modes are user mode, supervisor mode, and interrupt mode. User mode is the normal operating mode, where applications run. Supervisor mode is used for system-level tasks, such as managing hardware resources. Interrupt mode is used when an interrupt occurs, such as when a device signals that it has completed an operation.

Memory Management

ARM processors use a memory management unit (MMU) to manage memory. The MMU translates virtual addresses used by applications into physical addresses used by the processor. This allows applications to run in their own address space, protecting them from other applications and the operating system.

Thumb Instruction Set

ARM processors also support a compressed instruction set called Thumb. The Thumb instruction set uses 16-bit instructions instead of 32-bit instructions, which reduces code size and can improve performance by reducing memory access. Thumb instructions are a subset of the full ARM instruction set and are designed to be compatible with existing ARM tools and software.

Applications

ARM processors are used in a wide range of devices, including:

Mobile Devices

ARM processors are widely used in smartphones, tablets, and other mobile devices. ARM processors are popular in mobile devices because they are power-efficient and can be customized to meet the specific needs of the device. Some popular ARM-based mobile processors include Qualcomm Snapdragon, Samsung Exynos, and Apple A-series.

Embedded Systems

ARM processors are also used in many embedded systems, such as industrial control systems, automotive systems, and medical devices. ARM processors are well-suited for embedded systems because they are power-efficient and can be configured to meet the specific needs of the device.

Servers

ARM processors are also used in servers, particularly in data centers. ARM processors are gaining popularity in servers because they are power-efficient and can be customized to meet the specific needs of the workload. Some popular ARM-based server processors include Ampere Altra, Marvell ThunderX2, and AWS Graviton2.

Gaming Consoles

ARM processors are also used in gaming consoles, such as the Nintendo Switch and the PlayStation Vita. ARM processors are well-suited for gaming consoles because they are power-efficient and can be customized to meet the specific needs of the device.

Conclusion

In conclusion, ARM is a family of RISC architectures developed by ARM Holdings that are widely used in mobile devices, embedded systems, servers, gaming consoles, and other devices. ARM processors are known for their power efficiency, scalability, flexibility, and compact instruction set. The ARM architecture is based on a load/store architecture, and the instruction set is divided into three categories: data processing instructions, load/store instructions, and branch instructions. ARM processors are highly configurable and can be customized to meet the specific needs of a device. ARM Holdings is one of the leading semiconductor IP providers in the world, with over 130 billion ARM-based chips shipped to date.