Modern Motherboards: Out with the old and in with the “new” new

Guest post by Brian G:

In the real world, I work as a data and systems architect. A client surprised me this week by asking for a “10 year architecture plan” to include detailed hardware specifications. I found this interesting as we usually don’t venture more than five years into the future and in a scenario like this will specify the latest and greatest in server technology making sure the hardware has room for expansion. We can usually specify three to five years but without a crystal ball it’s difficult to know or even guess where processors, storage and especially motherboard technology will be ten years from now.

As home users we have some of the same issues in choosing hardware. Most of us can’t afford to lease our home computers and those of us who build our own (an expensive yet rewarding compulsion I picked up somewhere between the Pentium 2 and 3) find ourselves facing Moore’s law. Technology is evolving ever faster in computer hardware and a choice made today to upgrade may result in regret a couple of months later. The competition between AMD and Intel has the evolution of the processor and therefore the evolution of the processor form factor racing forward faster than ever before. The Pentium 3 and AMD K-7 chips brought speed to home users which had lagged behind the increases made in storage and user interfaces. The bottleneck in those days was found all over the motherboards, from the RAM all the way to the PCI bus, (if you can remember ISA then you can probably relate)

As long as the processor architecture doesn’t change, we can always swap out the chip if the motherboard allows it. Multi-core processors, high efficiency processors and 4-5 GHz chips are either here now or right around the corner. The performance gains, energy savings and new features make the decision to upgrade a difficult one to resist. My recent decision to replace an older Pentium 4 machine with a core duo one actually surprised me when I researched the various motherboard options and found features I had been reading about as “just around the corner” for quite a while were now appearing in the silicon such as pci-express, DDR-2 and 64bit support among other goodies. The already fast pace of hardware evolution gave way to a flood of new standards meant to open the data bandwidth of the system to approach that of the latest processors.

The PC and yes, even the Mac is actually a series of inter-dependant devices held together by the motherboard. Motherboards perform the critical role of routing data between the system components, translating control and data from peripherals such as your keyboard and mouse, reading and writing data between temporary storage such as RAM to permanent storage such as hard drives, CD /DVD drives and the soon to be flash based drives in addition to translating digital to analog or vice versa as needed. Some motherboards are true “all in one” devices with video, audio and networking peripherals built in.

Form Factors

Motherboards come in different shapes and sizes, sometimes a functional requirement and sometimes the all too common “proprietary format” specified by manufacturers for reasons we won’t bother with here. At one time or another you’ve heard of form factors which include, AT, ATX, BTX, Mini-ATX and even Nano-ATX. The form factor determines the overall dimensions of the board, the placement of components, especially external connections and the power supply pin-out and connector type. Your typical system administrator will probably have long and technical arguments for why a certain form factor, (usually one of the many I did not list) is better.

For the purposes of building or upgrading your system the best is one that fits the case you are using or plan to use, supports the technology you need and fits your budget. The most common form factors at this time are ATX, Mini-AX and Nano-ATX. As you might guess; the boards range in size with ATX being the largest, Mini-ATX smaller and Nano-ATX the smallest. Nano-ATX boards are used for specialty computers such as car PCs. ATX also refers to the power supply standard used in the latest boards which includes additional pins, SATA power connectors and often special connectors for high power graphics cards.

The Expansion Bus

The rectangular card slot connections which line the back-side of the motherboard provide the expansion bus. For years the most common bus types were AGP, (used for graphics) and PCI, (used for everything else, some graphics cards and anything not ISA but let’s skip ancient history). The importance of the various bus standard lies squarely in the amount of data bandwidth each one is capable of. The latest in bus technology is the PCI-express standard. Think of a PCI slot as a multi-lane highway capable of two-way traffic, traffic backups and so on. Each bus type has certain number of lanes and a “speed limit” for them. PCI-Express or “PCIe” is evolving even as you read this from version 1.1 to version 2.0 which will represent a doubling of its speed limit. PCIe 1.1 transfers data at 250 MB/s in each direction per lane. With 32 lanes available, PCIe has a theoretical transfer capability of 8 GB/s in each direction.

The standard bandwidth figure for PCIe v1.1 is given as 2.5 GB/s. PCIe v2.0 will be 5 GB/s. For comparison, just one of the lanes in a PCIe bus is close to 2 times faster than the old PCI standard. 8 PCIe lanes are equal to the fastest AGP bus. PCIe bus connections come in different sizes which range from 1x, 2x, 4x, 8x and 16x. The important thing is to check that your desired PCIe card has the required matching PCIe slot in the correct dimension. PCIe slots support vast improvements in the way in which data is communicated by means of layers in the data protocol. These allow even higher bus rates in future versions and a capability called “linking”. An even number of PCIe slots can be “linked” given specific support for linking built into the motherboard. This link allows us to combine 2 or more graphics cards for very high performance applications. As always, gamers and the design community are driving these capabilities. Depending on the graphics card vendor this is referred to as “SLI” or “Crossfire” capability.