If that's a general guide to the size and feature sets of microATX and Mini-ITX boards, what about the specifics of chipsets, sockets and CPU support?
The key distinctions here are between AMD and Intel platforms and in turn the differing limitations of the two form factors. Broadly speaking, when it comes to AMD CPU choice is not critical. That's because AMD has just one desktop CPU socket known as AM3. In terms of platform architecture, too, the choice of AMD-compatible chipsets doesn't really make a great deal of difference.
Consequently, whatever form factor you go for, any of AMD's current desktop CPUs should work. That includes everything from a weedy dual-core Athlon chip to AMD's finest six-core powerhouse. The latter is certainly an intriguing prospect in combination with a tiny Mini-ITX board.
It's also something that isn't currently possible with Intel platforms. The proportions of Mini-ITX are simply too small to cater for Intel's top LGA1366 socket, the triple-channel memory configuration it requires and other extras that are part of the X58 chipset including voltage regulators designed to cope with the six-core Gulftown CPU.
However, the slightly simpler LGA1156 socket is a goer in Mini-ITX format. That restricts the options and makes the top Intel option for the smallest form factor the Core i7 880 CPU. It's a quad-core chip with eight threads and significantly more processing power than AMD's fastest six-Core Phenom II X6 model.
Despite the incompatibility of its top six-core chips, therefore, Intel still offers the fastest performing processors for Mini-ITX.
MicroATX, however, is a very different story. Here there are almost no limitations in terms of CPUs, sockets and chipsets. Asus, for instance, will sell you a microATX board based on the X58 chipset and LGA1366 socket. In fact, the Asus Rampage III Gene also supports both AMD CrossFireX and Nvidia SLI in dual-card trim, has excellent cooling and packs a full range of overclocking options.
Speaking of chipsets, one of the reasons why modern SFF boards are even possible is the ever greater level of feature integration in the latest PC processors. Slowly but surely, everything from the memory controller and northbridge to the graphics processor is being assimilated by the CPU. Apart from making boards simpler and more space efficient, it also means that chipsets are becoming less critical.
Figuring out features
However, there are a few chipset related foibles specific to Intel and AMD that are worth noting. The AMD half of the equation is simpler with 785G and 880G integrated chipsets being the weapons of choice for both Mini-ITX and microATX boards.
There's little to choose between the two in terms of the main northbridge chip and integrated Radeon HD 4200 series graphics core. In fact, the 880G is nothing more than a minor revision of the 785G. Instead, it's the southbridge chip that tends to be critical for AMD platforms.
Motherboard makers do have the option to mix and match. However, you'll typically find the 785G chip paired with the SB710 southbridge while boards based on the 880G can be had with the newer SB850 model.
The key difference between the two is support for the latest SATA 6Gbps storage interface, a feature that will be increasingly important as ever faster solid state drives appear. The SB850 has it, the SB710 does not.
In the Intel camp, things are a little more complicated. For microATX boards, you have the full range of Intel chipsets on offer. The two discrete chipsets are the X58 for LGA1366 socket CPUs and the P55 chipset for LGA1156.
The former is Intel's flagship platform and offers high-end features, such as a triple-channel memory interface, more PCI Express lanes than you can shake a DX11 graphics card at and generally more bandwidth than you are ever likely to need.
The P55 chipset is less bleeding edge, but only slightly. It still delivers oodles of bandwidth for both the CPU and peripherals. What neither chipset can provide, however, is support for Intel's so-called Fusion CPUs and their integrated Intel HD graphics cores. These chips are currently sold under the Core i3 500 series and Core i5 600 series brand names.
In plain dual-core processor mode, they will tango with the P55 chipset. Exposing their graphics capabilities, however, requires an H55 or H57 motherboard wired up with video outputs. There's not much to choose between these two, but the H57 does come with a few extras.
For starters, you get a couple of additional PCI Express lanes for peripherals. On a full-sized ATX board, that might come in handy. But for an SFF system, it's arguably less irrelevant. More useful is the H57's native support for RAID configurations courtesy of Intel's Rapid Storage Technology. The H57 also offers a few more USB 2.0 connections.
What no current Intel chipset offers is native support for USB 3.0 or SATA 6Gbps. If you want either feature, you'll need to hunt down a motherboard with additional controller chips, pushing up the price.
Speaking of money, you may be surprised to learn that building your own system based on an SFF motherboard can actually be remarkably cost effective. Part of the reason is that smaller boards provide less opportunity for feature creep. Put another way, there's no space for board makers to add pointless features you're never going to use.
A good microATX board will have everything you need for a powerful PC but cost less than a full ATX board. You can take direct advantage of that by fitting a microATX board to a full ATX tower case. A smaller motherboard certainly makes for an easier build process and a less crowded case, too.
But we think it makes more sense to take advantage of the smaller board dimensions and go for compact SFF case. MicroATX cases complete with 450W PSUs can be had from as little as £25. If you want something with more firepower, it's best to buy the case and PSU separately.
Given the price of Shuttle systems, you might expect Mini-ITX cases to be much more expensive. But scan.co.uk, for instance, will currently sell you a Mini-ITX toaster case complete with 300W PSU for just £28. Add a motherboard and that's around £100 all in for a package that should match a £300 Shuttle for performance even if it's not quite in the same ballpark for build quality.
The sense of small
An SFF system, then, needn't be expensive or miss out on features that actually matter. But will it perform on a par with a full ATX rig? The simple answer is yes. Thanks again to the greater level of feature integration in the latest CPUs, small boards are capable of delivering big performance.
In our testing, there's literally nothing to choose between a full ATX board and a tiny Mini-ITX mobo if you are comparing, for instance, an Intel Core i7 870 processor running on the H55 at stock clock speeds. The smaller system will be just as fast. The same goes for AMD's chips.
What's more, given the bargain basement pricing of AMD's six-core chips, the idea of dropping a Phenom II X6 into a tiny toaster case certainly sounds like fun. What's more, even storage shouldn't be an issue. A dualdrive solution with an SSD boot drive for speed and a monster conventional hard disk for mass storage is the perfect SFF solution.
SUPERCOMPUTER: Looking to build a super triple SLI rig? MicroATX isn't for you.
What's more, even overclocking isn't off the menu. Gigabyte's H55N-USB3 Mini-ITX board will happily run Core i7 chips at 4GHz with the proviso that you have an adequate PSU and can find a decent CPU cooler compatible with the space constraints.
The one area where smaller systems arguably lose ground, however, is graphics. Most microATX and all Mini-ITX motherboards and cases lack support for SLI and CrossFireX multi-GPU graphics. That said, for most people a single, powerful 3D board is the best solution. Frankly, there are few situations where the likes of a Nvidia GeForce GTX 580 doesn't get the job done.
So, there you have it. A smaller board can make the basis of a compact, cost effective rig without compromising on performance or key features. Going small really is a very big idea.