ARM Processors

In recent years, "ARM" processors have gone from being an obscure niche market to a major player in computing.  We here at Woodcliffe IT decided to put together a brief history of the ARM processor, as well as a comparison of what the state of the art looks like.

History of the ARM Processor

Birth and Early History

ARM originally stood for Acorn RISC Machine.  It was a project started by the British computer company Acorn, who in the early days of personal computing made a number of popular low cost computers that had significant market share in the European market.  In 1983, Acorn decided they needed a new processor to replace the aging MOZ 6502 (a very popular processor seen in a number of applications such as the Apple I and the Nintendo Entertainment System, among others).  Acorn began a project to develop a new processor based on a "Reduced Instruction Set Computer" (or RISC) design philosophy.  The processor was finally ready to ship in 1986.  Acorn kept the processor as simple as possible, and the end result, the ARM2, had only 30 thousand transistors despite being a 32 bit chip, compared to its competitors like the Motorola 68k (around 68,000 transistors) or the Intel 80286 (134,000 transistors and only a 16 bit chip).  Despite (or because of) its simplicity, the ARM2 was actually quite fast, relatively low power, and cheap.

In the mean time, Acorn computer was in financial trouble.  In 1983, troubles with part suppliers meant that Acorn could only fulfill about 10% of the demand for their computers.  In 1984, with the production problems resolved, the home computer market collapsed, leaving Acorn with plenty of computers but no buyers.  Eventually Acorn's financial backers forced the company into a deal to sell itself to the Italian company Olivetti.  Acorn was forced to take its ARM processor division and spin it off into a separate company, ARM Holdings plc.

Acorn did eventually sell a line of computers based on the ARM processor they developed, but by this time Acorn's market share was shrinking and the systems never became very popular.  It looked like ARM would be doomed to fade into obscurity...

Outside Interests Save the Day

Luckily for ARM, companies other than Acorn became interested in the ARM processor.  The first company to show interest was Apple Computer, who were developing a portable computer system (called the Newton), and wanted a low power, high performance processor to drive it.  In cooperation with Apple, ARM Holdings designed and built the ARM6 processor which was used in the Apple Newton.  Unfortunately Newtons never sold well, and the project was canceled after a few years by the newly re-minted Apple CEO Steve Jobs.

The next company to show interest in ARM was Digital Equipment Corporation, or DEC.  Instead of contracting with ARM Holdings to design a processor suited to their needs, DEC proposed a very different deal.  DEC would license the design of the ARM processor and produce their own processors.  This unorthodox deal turned out to be the saving grace for the struggling ARM architecture.  ARM Holdings had to do very little work, just send the schematics and specifications for their processor.  DEC could do as they pleased with the information, as long as they paid ARM royalties.  This kept ARM Holdings costs low, they could sit back and let DEC do the work for them.

DEC took the ARM architecture and made extensive modifications, calling the result the StrongARM.  StrongARM was fast and very lower power (for the time), consuming about 1W of electricity.  DEC envisioned many uses for ARM, especially in embedded electronics, a fairly accurate prophecy of what the ARM processor is used for today.

Unfortunately DEC entered into serious financial troubled and eventually was forced out of business.  DEC's skilled engineers and extensive intellectual property was snapped up as quickly as possible by other large technical companies.  Intel ended up buying the StrongARM division from DEC in 1997, and continuing the development of the processor, selling the processors as StrongARM and later as XScale.  It was during this period that ARM started to see significant usage in portable electronics.  During the PDA boom of the late 90s and early 2000s, ARM processors were used in Microsoft Pocket PC devices and in PDAs based on the Symbian operating system.  Intel decided to concentrate on their x86 processors and sold the XScale design to Marvell Technology Group in 2006.

ARM Today

ARM Holdings, encorraged by their very successful licensing deal with DEC, left the business of actually building processors and focused entirely on developing the ARM architecture and on licensing the results to any company in need of a flexible processor architecture.  This business has been very successful for them.  From the early days of selling a few thousand processors per year, ARM processors are now produced at the rate of about 5 billion per year.

Unlike architectures like x86 or PowerPC, ARM is sold as a design to companies with the capability to produce them.  These companies can stick closely to ARM's reference designs, or they can modify the design extensively to suit their own needs.  This flexibility has resulted in an enormous range of processors, ranging from small low power processors suitable for use in a wristwatch or home appliance to powerful multi-core designs capable of powering computer servers or high powered smartphone and tablet computers.

ARM processors are usually differentiated by their instruction set revision.  Newer instruction sets include many performance boosting features and are used in high performance devices such as smart phones and tablets.  Older revisions of the ARM instruction set are still used, since they tend to be simpler, cheaper, and lower power, so are suitable for applications where performance isn't an issue.

Below is a list of current ARM instruction set revisions along with common applications:

ARM Holdings naming conventions can be a bit confusing.  Generally they work as such:

ARMv7 -  If the ARM is followed by a "v" then a number, this indicates a version of the ARM instruction set.  Newer instruction sets are backwards compatible with the older ones, but software for newer instruction sets may not work on older ones.  Generally newer, more powerful ARM processors use the latest instruction set, while lower power processors used in embedded applications may use an older instruction set.

ARM11 - The ARM is followed by a number, but not by a "v".  This is a reference design.  ARM traditionally will design "sample" processors, then sell the design to companies who are free to modify and produce it.  The number indicates what reference design it is, and not which instruction set it uses.  For instance, the ARM6 uses the ARMv3 instruction set, while the ARM11 uses the ARMv6 instruction set.

ARM Cortex A8 - The newer ARM reference designs are usually noted in a new format, "Cortex" followed by a letter and a number.  The letter and number do not indicate which instruction set is used.  Cortex processors are generally either ARMv6 or ARMv7, although new reference designs for ARMv8 will probably be called "Cortex" as well.

Common uses for ARM Processors

Because of the design licensing scheme, companies are free to modify ARM to work well in whatever application they wish.  This has led to an astonishing variety of uses for ARM.  Some common ones include:

Mobile Computing - Smartphones and tablets have become a major market.  Because of the sophisticated operating systems and games that are often run on these devices, they tend to use the latest and greatest ARM instruction sets and reference designs.  Common modifications include adding powerful 3D graphics acceleration and hardware video playback.  Modifications to add features commonly found in smartphones (integrated cellular radios, baseband processors, etc...) are also common.  Companies that produce ARM processors for mobile computing include Samsung, Qualcomm, nVidia and Texas Instruments among many others. Roughly 40% of United States cell phone owners have smartphones as of Q3 2011 and that number is expected to climb to over 50% by the end of 2011.  Market research companies IMS and IDC expect total worldwide sales of smartphones to be between 420 and 475 million in 2011, almost all of those smartphones using ARM processors.

Set Top Boxes - We demand a lot out of our cable boxes, DVRs (Digital Video Recorders) and streaming media boxes.  DVRs must have processors powerful enough to playback high definition video smoothly, but low cost and low power consumption are also important factors.  Due to recent leaps in ARM processor performance, set top boxes powered by ARM processors are becoming more popular.  The Apple TV 2 uses an ARM processor similar to the one found in the iPhone 4, which replaces an Intel x86 processor in the Apple TV 1, allowing the ATV2 to be smaller and more energy efficient.  New Google TV boxes are set to switch over from Intel x86 to ARM, again for cost/power/performance reasons.  Currently the worldwide market for set top boxes is roughly 350 set top boxes according to ARM, and their current market share is about 35% and growing.  Major manufacturers of set top box oriented ARM processors include Mediatek, Samsung and Texas Instruments.  Set top boxes also frequently use processors intended for smartphones and tablets, which already have low power consumption and excellent video playback capability.  ARM processors are also frequently seen in Blu-ray and even DVD players.

Digital Cameras - Digital cameras are miniature computers that have to process massive amounts of image data very quickly and write it to your storage card.  Many camera manufacturers have chosen ARM processors for their low power and high performance characteristics.  One characteristic that comes in handy is ARM's ability to easily be modified with co-processors and new extensions, allowing camera companies to add on accelerated image processing hardware easily.

Personal/Industrial Computing - Many companies are very tempted by the low cost of ARM processors.  Profit margins on laptops and personal computers are razor thin, and the market for cheap computers is very large.  Using an ARM processor could save costs compared to more expensive x86 processors, giving manufacturers an edge in profit margins and low price points.  As of yet, attempts at building ARM powered laptops have not sold well, mostly due to a lack of a suitable operating system.  Microsoft may give the effort a major boost with Windows 8, which will support ARM processors as well as x86.  Many computer manufacturers also see an opportunity for ARM in the server market.  In many applications, many cores is more important than the per core performance, and low heat/power requirements are also important for densely packed server rooms.  ARM potentially could solve many of these issues.  Since each ARM core uses very little power, you can pack many more ARM cores into a server than you could with x86 cores, while still using the same amount of power.  HP has recently announced that they will be introducing a line of ARM powered servers in the near future, and ARM Holdings has been working on reference designs for server-spec processors.  Currently the major manufacturer of server class ARM cores is Calxeda.

There are many other markets in which ARM holds a significant market share, too many to list in fact.  The four above give an example of ARM's increasing performance and the new markets opening up to the ARM platform.

Threats to ARM

ARM holds a complete monopoly over the smartphone market, so there is little short term threat to them there.  Since they own the entire market, their growth is limited to the growth of the smartphone industry.  As such, ARM has recently been trying to expand into other markets, where there is significant competition.

At the moment, ARM is targeting lower power x86 chips as likely candidates for replacement with higher end ARM processors.  This means they have made an enemy of Intel, who doesn't like having their market impinged upon.  Intel launched the Atom processor in 2008 as a direct competitor to ARM based processors.  The Atom is the lowest power x86 processor sold by Intel to date, and it is also relatively inexpensive.  However, Intel does not have much experience designing ultra-low power processors (under 10W), so the Atom's dominance over ARM processors is questionable.  The lowest power Atom processor available uses 2W at "full power" and about 100mW in power save state.  Compared to the ARM Cortex A8, which uses about 1.25W at full power and an amazing 7mW in power save mode.  Since most portable electronics spend most of their time in "power save", the ARM processor has a 14x advantage in power consumption.  The Atom processor is not particularly fast, nor does it include graphics or video acceleration technologies built into the processor (although these can be added externally).  This means that although the Atom has a moderate computational advantage over the ARM processor, for many common tasks like watching videos or playing 3D games, the ARM processor will actually outperform the Atom.

ARM has also recently decided to target the server market.  This is a huge shift for them.  While Intel does not have much experience in low power processors, ARM is lacking in experience in high power processing.  The ARM architecture does not have any inherent limitations that prevent it from being used in high performance computing, it is just that ARM has spent the last 15 years designing low power, low performance processors, and so they do not have much know how in designing high power, high performance processors.  Currently, the highest power ARM reference designs use roughly 2W or so of power.  Intel and AMD's high end server processors can use 130W or more, 65x more power.  The performance difference between the current ARM designs and high end server processors is also significant, although ARM still maintains an excellent performance/power ratio.