ARM or Advanced RISC Machine is a specific family of microarchitecture based on the instruction set architecture called reduced instruction set computing or RISC developed by British semiconductor and software design company Arm Ltd. Processors based on ARM architecture have been found in portable devices such as smartphones and tablet computers, as well as gaming consoles, media players, smart devices, desktop, and laptop computers.
The growing popularity of ARM processors over x86 architecture from Intel Corp. and other architectures based on complex set instruction computer or CISC, and even those based on RISC have been attributed to specific advantages and applications, as well as the flexible business model of Arm Ltd. that provides a compelling case for licensing ARM architecture and choosing ARM processors against counterparts from traditional chipmakers.
Understanding the Popularity of Advanced RISC Machine or ARM
Advantages and Applications of ARM Architecture and ARM Processors
Suitable for Battery-Operated Electronic Devices
One of the notable advantages of ARM architecture and the resulting ARM processors is that they have good performance per watt. Thus, they are suitable for battery-operated consumer electronic devices in which energy efficiency is an indispensable feature. Take note that Android smartphones and tablet computers, as well as iPhone and iPad products from Apple Inc., use processors based on ARM architecture.
Chipmakers and device manufacturers choose this architecture if they want to prioritize energy efficiency. Furthermore, aside from being more energy-efficient, ARM processors also dissipate less heat than processors based on other architectures. Devices running these processors are less prone to overheating and require fewer heat management components.
The capability of a processor based on Advanced RISC Machine architecture to run on low power is suitable for the 3.5-watt Thermal Power Design requirement of mobile devices. Note that mid-tier to top-tier Intel processors struggle to scale down below 5W. It is important to note that the alternative x86 architecture from Intel targets peak performance.
Of course, prioritizing power efficiency does not mean that ARM processors lack processing power. CPUs based on this architecture sometimes exceed the performance of x86 processors for applications that exist on both architectures. Note that the iPad Pro 2020 from Apple, which uses the ARM-based A12Z Bionic processor, scored higher in benchmark tests than the mid-tier and high-end processors used in laptop and desktop computers.
Big.LITTLE Heterogeneous Computing Architecture
A significant feature of ARM architecture that allows it to achieve low power consumption and promote energy efficiency is heterogeneous computing. By definition, heterogenous computing is a specific system design consideration that involves using different processors, cores, or other hardware components within a single system.
Systems with heterogonous computing have notable energy efficiency and performance advantages. For example, the components of an ARM-based CPU include not only the same type of processors but other dissimilar coprocessors that have specialized processing capabilities intended for handling particular tasks.
A more specific example is the multi-core system of Snapdragon and MediaTek processors respectively from Qualcomm and MediaTek, and the A-series Bionic Chip from Apple. Each uses a single instruction set architecture, but they have cores with different clock speeds. Some of the cores are designed for handling low-power tasks, while the remaining ones are activated only for resource-heavy operations.
The idea behind heterogeneous computing is simple. Fundamentally, it involves building an architecture that enables different CPU components with different performance and power capabilities to work together to improve efficiency. The specific ARM big.LITTLE architecture first introduced in 2011 allows an ARM-based processor to share the workload across high-performance and low-performance CPU cores.
Has the Advantages of RISC Architecture
Remember that ARM architecture and ARM processors are based on reduced set instruction computing architecture. Hence, it inherently has the characteristics and advantages of RISC. These include a smaller number of instruction formats, few numbers of instructions, and few addressing modes. A RISC processor tries to perform one thing only per instruction, and it can execute difficult commands by merging them into simpler ones.
Another advantage of reduced set instruction computing architecture is that it uses a fixed length of instruction, which is easy to pipeline, because RISC functions use only a few parameters. There is also the time advantage. Each instruction only takes up one cycle, thereby maximizing operation speed while minimizing the execution time. It supports more registers to enable less time on loading and storing values to the memory or cache.
The speed of the operation can be maximized while minimizing the execution time. Because it lacks complex instruction decoding logic, it supports more registers, thereby allowing less time on loading and storing values to the memory or cache.
With regard to chip designers and manufacturers, RISC processors are easier to design and deploy than CISC processors. It also has a lower per-chip cost because the architecture requires smaller components. Less chip space is used due to the reduced instruction set. Required transistors are also fewer because the decoding logic is simple. More general-purpose registers can be fitted into the central processing unit.
Business Model and Licensing Scheme of Arm Ltd.
There is one key difference between traditional chip supplies such as Intel Corp. and Arm Ltd. Conventional chipmakers design and manufacture chips. On the other hand, Arm Ltd. designs semiconductor chips and licenses the principal technologies as intellectual property. It does not produce, market, and sell its own microprocessing units. This flexibility is one of the reasons why Apple ditched Intel for ARM.
More specifically, Arms Ltd. provides three types of licensing agreements: core design license, Built on Arm Cortex Technology license, and architectural license. The architectural license allows licensees to design their own chips based on the Arm architecture. Some of the notable holders of Arm licenses include Advanced Micro Devices, Inc. or AMD, Apple Inc., Qualcomm Incorporated, Nvidia Corporation, and Samsung Group, among others.
A licensing business model provides several advantages. For starters, it provides other chipmakers and device manufacturers a considerable degree of freedom and flexibility with regard to controlling their costs. In addition, companies such as Apple can develop their own processors based on ARM architecture and optimized for its operating system and applications. Licensing allows companies to build hardware around the software.
In contrast, there are downsides to the traditional models used by companies like Intel. Computer manufacturers are stuck from paying whatever a particular chipmaker decides to charge for its processors. Both manufacturers and developers would also need to build their hardware configurations and design their software around the processor, thus limiting their capabilities. Note that these two are some of the key issues with x86 architecture.
Disadvantages and Limitations of ARM Architecture and ARM Processors
Incompatibility with Several Software
The x86 architecture has been the standard architecture used by chipmakers and computer manufacturers for several years. Take note that producers of Windows-based desktop and laptop computers have used processors from Intel and AMD. Apple started using Intel processors in its Macintosh computers beginning in 2005. The entire ecosystem has been accustomed to developing and utilizing software or apps based on x86.
Hence, compatibility is a considerable limitation of ARM architecture that affects its full adoption by computer manufacturers. A Windows operating system based on x86 would not natively run on an ARM-powered computer. It is essential to highlight that several general-purpose off-the-shelf applications were developed for x86 systems. Intel and AMD have a considerable share in the personal computing market.
But industry leaders are also moving away from x86 architecture. Microsoft first announced its plan to develop a version of Windows and other applications compatible with ARM as part of its partnership with Qualcomm. The company has eventually launched the Surface series of Windows computers in the market running ARM-based Snapdragon processors.
Apple has also announced its shift from Intel to its custom-designed processors based on ARM architecture as part of its product strategy. In November 2020, the company launched the first models of the MacBook Air, MacBook Pro, and other Mac computers featuring the Apple M1 processor. To address compatibility issues, Apple distributed devices for developers and has rolled out Rosetta 2 to allow native x86 apps to run in the new ARM-based macOS system.
Has the Disadvantages of RISC Architecture
Of course, ARM architecture and ARM processors also share the drawbacks of RISC architecture. For example, the aforesaid time advantage of RISC has a disadvantage. Compilers need to break down high-level instructions into many simpler instructions. In addition, rearranging CISC code to a RISC code results increases the code size. The quality of this code will depend on the compiler and instruction set of the machine.
From the perspective of compilers and software developers, developing programs or applications for RISC and ARM requires more effort when compared to developing for CISC-based architecture such as x86 architecture. The performance of the processor depends on the programmer or software developer.
The simplicity of a processor based on a reduced instruction set computer puts a lot of stress on the software or application. Another disadvantage is that feeding instructions require very fast memory systems. Specific architectures and processors based on the general RISC architecture require large memory caches.
A Note on the Capabilities of the Programmers
It is worth highlighting that complex instruction set computer or CISC architecture is focused more on the hardware. In contrast, those based on reduced instruction set computer or RISC architecture are focused more on the software. CISC tends to be more hardware-specific, while RISC is usually more software-specific.
Hence, the performance of architectures and processors based on RISC such as ARM depends on the capabilities of the programmers and the quality of their software and application. There must be a proper execution of the instruction, and this depends on the programmer. The quality of the instruction also determines the performance of an ARM processor.
Note that RISC-based processors demonstrate poor performance once fed with instructions or codes written with low quality. It is for this reason that ARM processors require highly skilled programmers and software developers.
Possible Threat to Developer and Consumer Options
A valid concern over the growing popularity of ARM architecture and the corresponding processors center on the possibility of limiting options available to others as companies integrate vertically their supply chains and value chains. Remember that Arm Ltd. only provides a license. Companies can design and produce their own processors based on this license.
The move of Apple to ditch Intel over its custom-made ARM-based Apple M-series processors has been welcomed with praise and criticism. Of course, this decision gives the company numerous competitive advantages ranging from reduced dependence on a third-party chip supplier and better control over its entire product roadmap and ecosystem.
However, as a particular company gains more control, third-party groups and consumers lose their options. Critics fear that Apple will have more control over app developers for the macOS operating system. Furthermore, the company will limit the choices of its consumers because of the prevailing compatibility issues between ARM and x86 processors.
Other companies could follow the lead of Apple. However, the current reality is far from these assumptions. Manufacturers of consumer electronic devices such as Microsoft and Samsung still depend on third-party chipmakers because it is more efficient for them to outsource this production requirement rather than developing their own in-house capabilities. The barrier to entry for chip design remains high. So far, Apple is the only company with a tighter and more vertically integrated supply and value chains.