ARM vs x86

11/17/2012 7:41:34 PM

ARM chips account for over 95 per cent of the mobile market, but why? Let's analyze the ARM and x86 architectures

Intel is the undisputed leader of the desktop and laptop CPU market, with the most recent figures estimating that 80.2 percent of all processor shipments come from the company. In the embedded and low-power market, however, it's a bit player: chips based on designs from ARM, a British company born out of the ashes of Acorn Computers, account for the overwhelming majority of processors in the mobile market.

Intel isn't comfortable with this situation, and the company has made significant moves in recent years to assault the mobile market from the unfamiliar position of the underdog. The differences between ARM and Intel are far greater than those between Intel and its nearest desktop rival, AMD; they also extend beyond different business practices to the very architecture on which the processors are based. But what difference does it make to the consumer?

The origins of ARM

Description: The origins of ARM

ARM Holdings, the company responsible for the architecture that's proved so successful for low-power devices, wasn't always known as ARM. Launched as an in-house project to create a custom processor for British micro computing pioneer Acorn, Acorn RISC Machines (later rebadged as Advanced RISC Machines when Acorn was delisted from the stock exchange after the great microcomputer crash of 1984) was incorporated in 1990asajointventure between Acorn, Apple and VLSI Technology.

ARM's primary design point, and the focus for lead engineer Sophie Wilson, was to create low-power, energy-efficient CPUs as a response to what was seen as the wasteful design of rival chips from companies such as Motorola and Intel. Despite industry-leading innovations, the first ARM chips weren't a commercial success; Acorn's Archimedes and RiscPC product lines would use the chips, but only Digital Equipment Corporation (DEC) would license the technology. Even Apple, a partner in the ARM project, refused to use the chip in its desktop computers.

ARM chips' simplified design and reduced instruction set computer (RISC) architecture meant that they drew significantly less power than rival processors, however, and as companies started to develop personal digital assistants (PDAs), and other precursors to today's tablets and smartphones, the chips looked increasingly tempting. Fast forward to today/, and ARM boasts a market share in smartphones and tablets of over 95 percent, while having almost zero presence elsewhere - exactly the opposite of Intel.

ARM'S advantages

Description: ARM's processor designs are becoming increasingly complex, while Intel's Atom grows simpler.

ARM's processor designs are becoming increasingly complex, while Intel's Atom grows simpler.

However, what makes ARM's designs so popular for low-power computing? The company certainly has a different approach to the market from that of Intel, where the latter produces its own chips; ARM produces no physical goods whatsoever. Instead, it licenses its intellectual property (IP) to third parties who can either start building ARM-based processors immediately using an off-the-peg design, or build on ARM's work to create a custom chip. ARM's licensees include Apple, Marvell, Nvidia, Texas Instruments, and at one point, even Intel itself.

A simple difference in tactics can't account for ARM's stellar success, however. Perhaps the biggest contributor to ARM's domination of the mobile market comes from the architecture itself. Based on a reduced instruction set, Wilson and his colleague Steve Furber tried to replicate the efficiency of MOS Technology's 6502chip, which had a more streamlined approach than that of complex instruction set computer (CISC) competitors used by Intel. In short, fewer instructions means fewer transistors.

While Intel's 80286 design packed 134,000 transistors, the first production ARM processordesign-ARM2- outperformed it with just 30,000 transistors.

Fewer transistors also mean a cheaper, smaller chip, and these are key considerations in mobile computing. Fewer transistors also mean a lower power draw, with extended battery life far beyond what can be offered by a CISC- based design using a similar manufacturing process.

ARM, through its multifarious licensees, was also an early adopter of the concept of system-on-chip (SoC) design. Where a traditional processor requires multiple supporting components, such as the Northbridge and Southbridge, an SoC packs as much of this as possible into a single chip. By allowing manufacturers to concentrate on the user-facing elements of design, while simply dropping in a single chip that handles central processing, graphics processing, bus processing, communications and more, ARM became the simplest chip setup on the market. Although some manufacturers still prefer to produce pure or near-pure ARM CPUs, heavily integrated SoC designs such as those from Qualcomm account for a large chunk of the market.

Intel fights back

Description: Intel's decision to create an Atom SoC design gives it major competition to pitch against ARM's IP

Intel's decision to create an Atom SoC design gives it major competition to pitch against ARM's IP

Intel is no stranger to the advantages of ARM's RISC-based design, of course. As part of a lawsuit settlement with DEC, Intel gained an ARM licence and used it to produce its StrongARM processors for the early PDA and embedded markets. That licence would later be sold to Marvell, with Intel preferring to concentrate on its own x86 architecture.

For a long time, Intel allowed ARM to dominate the low-power embedded market, but in the past few years the company has been hitting back. Although originally designed for the netbook market, Intel's Atom processors-x86 CISC chips designed for low-power usage - are being pitched as a major competitor to ARM's designs in the burgeoning tablet and smartphone markets. Its most recent Atom product, the Atom 'Medfield' Z2460, is a SoC that's already won support in smartphones and tablets from Lenovo, Asus and Acer.

Intel's attempt to fight back against ARM has been helped by a shift in processor design: where olderx86 chips were pure CISC designs, modern chips have more in common with the RISC methodology preferred by ARM, with a CISC overlay used to provide compatibility with existing x86 code. As a result, Intel can shrink its designs considerably/, and while it's unlikely drop to the price of a rival ARM chip, Intel also has huge cash reserves on its side.

ARM's licensing model means that, despite its huge popularity, it has razor-thin margins. ARM's revenue for the last quarter was $314.1 million, while Intel's was $12.45 billion over the same period. ARM's licensing model means significantly lower operating costs, of course, but the result is clear in the profit figures:

$92.85 million compared to Intel's $2.55 billion. That extra cash gives Intel the room to invest in research and development, which is slowly but surely bringing the company close to parity with its British rival.

The current market

Intel is cagey about detailing the number of transistors in its Atom Z2460 SoC, but we know it has a 12x12mm package-on-package (PoP) design. That proves Intel can shrink its parts enough to compete with companies such as Samsung, which makes a series of 12 x 12mm ARM parts in the Exynos family; Qualcomm was managing 14 x 14mm packages when it used a 45nm process for its Snapdragon S1 family.

Description: Intel's new Atom SoCs are expected to gain a small but important foothold in the mobile market

Intel's new Atom SoCs are expected to gain a small but important foothold in the mobile market

Intel still has some way to go, however. The current-generation Atom SoC might be a similar size to its ARM-based counterparts, but this was achieved by cutting a few corners. Where Samsung's Exynos parts are dual- or quad-core, the Atom Z2640 has just one core. Although dual-core parts are due from Intel, it hasn't yet revealed their size, or what effect the extra core will have on power draw.

While Intel is working on shrinking its parts and developing competitive SoC designs, ARM is looking to break into Intel's primary market. The latest ARMv8 instruction set introduces 64-bit support for the first time, along with hardware virtualization instructions and other features that make it suitable for use in servers. With the growth of cloud computing spurring interest in so-called micro servers, Intel could be fighting off ARM in its most profitable market, even as it tries to break into ARM's mobile stronghold. In short, ARM's designs are becoming more complex, while Intel is simplifying its own. The lines between RISC and CISC have never been so blurred.

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