Original URL: http://www.theregister.co.uk/2012/10/23/arm_windows_8/
Microsoft: Welcome back to PCs, ARM. Sorry about the 1990s
Come in from the cold, we've got Windows RT tabs to flog
Analysis More than two decades after the alliance of Intel and Microsoft drove ARM from the battleground of personal computing, Microsoft is warmly embracing the low-power processor designer for Windows 8.
ARM was squeezed out of the then emerging and subsequently dominant platform of the time, the desktop PC, as computer makers coalesced around Intel chips running Windows software.
Not that ARM cared that much: billions of its processor cores now ship every year and are used in just about everything else from phones to handheld games consoles.
And the Cambridge-based biz hasn't been entirely absent from computers as we know them since the end of Acorn's ARM-powered Archimedes and RiscPC machines, the last model of which was launched back in 1994: ARM made a decent run of it on netbooks and its technology is at the core of the Apple iPad. Funnily enough, Apple used an early ARM processor design in its touchscreen Newton gadget in 1993.
But with Windows RT - aka Windows 8 on ARM - chips designed by the British biz will run an OS from Microsoft, the company that hastened ARM's retreat into embedded systems last century. Yet the architecture could now find its way back onto the majority of our desks.
Much of the talk on Windows 8 has focussed on the Pro edition, which will run on yet more Intel-based desktop PCs and their latter-day contemporaries - laptops and Ultrabooks - it's the version coming this week called Windows RT that has been built by Microsoft to run on ARM-compatible processors.
So what is Windows RT and what should we expect from the union with ARM, now a FTSE 100 company?
ARM-powered computers have been announced by Dell, Lenovo, Samsung and ASUS. Microsoft also has an ARM gadget coming as an instance of the Surface tablet announced in June. Surface will come in Intel-powered form too, but that won't run Windows RT as the diminutive version of Windows 8 will not be available as a packaged or downloadable product. Like a phone operating system, it will only be possible to get Windows RT on a device so you'll take what Microsoft gives you and be grateful for it.
Chips using ARM's licensed designs are widely lauded for their performance and battery life, not least by Microsoft's Windows supremo  Steven Sinofsky.
This should be a good thing for users, meaning devices don't get hot, less charging, and snappy responses to commands. But is Sinofsky right to make such claims?
Where this RISCy business began
ARM was spun out from British computer maker Acorn in 1990 to develop and market the eponymous chip architecture, which was built for the follow up to the iconic BBC Micro - the Acorn Archimedes. ARM's processor family offered outstanding performance for a desktop computer at the time, but the Archimedes was hampered by Acorn's idiosyncratic operating system RISC OS, which bore little resemblance to what students would see and use at work when they left school.
Applications would plot Bézier curves in real time and render three-dimensional-models into two-dimensional printouts (complete with tabs to be folded and glued to construct the paper model) but then require combinations of mouse buttons and dragging just to save a file. Its menu-driven, drag-n-drop-based user interface was alien to anyone used to Microsoft's Windows.
This raw processing speed, we were told at the time, could be attributed to the Reduced Instruction Set Computing (RISC) architecture of the ARM processor beating at the heart of the Archimedes, the processor which is the grandaddy of the chip now found in every mobile phone, and the chip that will be running Windows 8 RT.
RISC systems are not, despite what we were told, inherently superior to Complex Instruction Set Computing (CISC) systems, such as those built by Intel*. In fact the difference between the two is often hard to spot, there being no definitive definition of either term. Basically it's about how many steps are involved in processing each instruction in the software being run, and how many instructions are needed to do anything useful.
So, for example, a CISC processor will have a single instruction that swaps the contents of a specific register with a 32-bit value stored in a specific memory location. The RISC equivalent may have to copy the register's original value to some temporary location, then read the desired data into the register, then move the original contents into the new-available memory location - accomplishing the same thing, but with three instructions instead of one**.
This immediately makes a mockery of processor specifications - RISC chips always do well when comparing MIPS (Millions of Instructions Per Second), but when so many more instructions are needed that's hardly relevant. Clock speed, similarly, becomes moot, especially when Intel started performing multiple instructions within a single tick.
That's not to say the early ARM processors weren't fast - they were very fast and managed to consume hardly any power at all. But much of the company's success can be blamed on the triumvirate of Acorn, Apple & VLSI, which together set up ARM Holdings in 1990 and pushed it into licensing designs rather than baking its own silicon chips.
Having failed to hold onto the desktop, ARM retreated into embedded systems, drawing up small processors that ended up controlling disk drives and the like. In these particular environments power consumption isn't a big deal, but physical size is important as is heat production, which in turn leads to the development of more very small power-efficient chips suitable for living off battery power.
Size, then, would seem to be the big thing as far as Microsoft is concerned. When it comes to Microsoft's Surface, the ARM device will weigh 676g and be 9.3mm thick versus 909g and 13.5mm for the Windows Pro Intel machine. Both feature a 10.6-inch HD display.
ARM has never made chips, instead it flogs copies of its blueprints to component manufacturers who in turn use fabrication plants to churn out the electronics. It's a model it still follows today and one which gave confidence to product manufacturers that they'd still be able to fabricate and buy the same part in a decade - something which matters a lot to hardware people.
When Personal Digital Assistants (PDAs) came along ARM was the natural choice - and even Intel eventually acquired the designs to ARM-compatible processors in a lawsuit settlement with DEC, which had worked with ARM to create the StrongARM chip. Palm convinced its chip provider, Motorola, to license ARM's design too and in 2001 Microsoft announced it would be dropping support for the Hitachi SH-1 and MIPS designs and making ARM the only platform for its mobile OS (PocketPC).
The freedom to tinker - why Apple et al really want an ARM licence
These pocket computers put a huge strain on the processors, forcing ARM to extend the design and innovate to the point where its cores aren't as RISC as they used to be, even if they are still frugal on the power and cool to the touch. But it's not just technical innovations that make ARM the architecture of choice: the ability to change silicon chip suppliers and tweak designs has also been vitally important to the success of the platform.
A really large manufacturer might stump up a lot of cash to license ARM's core architecture to tweak as they will, but there are only a handful of such companies (including Qualcomm, Marvell, Infineon and, mysteriously, Microsoft). The majority of licensees take a design as it stands and integrate it into their own chips. That's what Samsung and Apple did for iPhones and iPads - until Apple fiddled with the blueprints to create the iPhone 5's A6 chip. It serves to illustrate the advantage of a licensed architecture (like ARM) over a chip shipper (like Intel).
Samsung used to make the chips for Apple's iOS gear by integrating a load of functionality (including an ARM core or two) into a single piece of silicon known as a System on a Chip (SoC). Then Apple had a bit of a falling out with Samsung, so it decided to make its own SoCs, which entailed taking an ARM architecture licence from those nice chaps in Cambridge and rolling up its sleeves. Had Apple been getting its chips from Intel or similar, then the shift in providers would have been a lot more challenging: it couldn't, for instance, just walk off with Intel's silicon designs and hand them over to, say, AMD.
For smaller players the argument is even more compelling. They can design one SoC package and contract its manufacture out to multiple suppliers, enabling them to negotiate the best price while being confident that supplies aren't going to totally disappear if one factory were to end the production run.
The popularity of ARM is no doubt behind Microsoft's decision to support the architecture with Windows RT. Microsoft needs to bring in more manufacturers, and get some innovation in design, and those companies will be much more interested in designing around parts available from multiple manufacturers, not to mention capable of supporting multiple operating systems.
Compromise all round?
So ARM is an excellent choice, regardless of the accuracy of Sinofsky's claims on power and performance. Intel has advanced in leaps and bounds since it became clear that mobile was the place to be, but that might not help when it's the business model - the licensing of ARM - that is the real driver for Windows RT as Microsoft seeks raw growth from a starting point of zero.
So, Microsoft gets proliferation. What do users of Windows RT devices get aside from smaller units that last all night and don't burn a hole in your lap?
On the software side, don't expect your standard Windows apps to run on the ARM machines as Windows RT won't run software built for Intel's IA32 and X86-64 family of processors - a point of huge contention between Microsoft and Intel. Windows RT users won't be allowed out of the user interface formerly known as Metro, so there will be no classic Windows desktop-style mouse and keyboard experience.
On the plus side, Windows RT will come with bundled apps instead - versions of programs found in Windows 8 Pro except Windows Media Player. Also, there will be a version of Office 2013 called Office Home & Student 2013 RT that will include Word, Excel, OneNote and PowerPoint but no Outlook.
ARM has made its name without its name being obvious: only those inside the business could really spot an ARM phone or tablet, and most consumers aren't the kind of engineering geeks who pay attention to the kind of chipset their machine is running.
If Windows RT becomes a mass market, then this will suit the kinds of box shifters who are not interested in the high end, where brand matters and computers need recognisable logos. ARM is quite happy in this space, for the moment at least.
ARM has some distinct technology advantages, but it's the business model - licensing - that's really driving Microsoft here and that should help keep Microsoft happy for a while. As for users? They get one of the world's most popular software suites, Office. The rest? Well, you didn't want your old software did you? ®
* Since the Pentium Pro, Intel processors have used RISC-like inner cores to break traditional CISC x86 instructions into smaller steps. However, compiler writers and anyone else working with x86 assembly language have to use Intel's rather CISC instructions when developing software.
** This is just an example of RISC versus CISC. ARM's instruction set actually includes a SWP instruction which does indeed switch the contents of a register with a memory location in one atomic operation. It was added in the ARMv2a architecture, and is essential in multi-threaded programming.