Microsoft: Welcome back to PCs, ARM. Sorry about the 1990s

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.

ARM supplies chip designs to 95 per cent of the world's smartphone market; ARM has about 10 per cent of the mobile computing market today but reckons it can hit more than half by 2015.

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? ®

Mootnotes

* 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.