DTX: An Early Primer

At the 2007 Consumer Electronics Show, AMD announced a new form factor for smaller computers. They call it DTX.

DTX is yet another attempt to create a computer form factor smaller than the very familiar ATX form factor. It attempts to resolve some of the issues with ATX, as well as make some adjustments to create a more compact desktop computer. After all, a typical ATX case mostly contains... air.

In a Nutshell

The sales pitch for DTX is that it is an open industry standard (usable by anyone, cheap or possibly for free) meant to help system builders create smaller, quieter systems. It is at present a fairly loose (and still under development) specification, placing relatively few restrictions on particular implementations. AMD aims to keep it that way, specifying only "a minimum set of parameters necessary for interoperability"

The main focus, as with most computer form factors, is the motherboard. DTX defines two possible sizes: the "normal" DTX motherboard measures 200 mm x 244 mm (slightly smaller than microATX's 244 mm x 244 mm), and a smaller Mini-DTX size (200 mm x 170 mm) will also be available. The mounting holes and other physical-fit concerns are made to be consistent (enough) with ATX, so that a DTX motherboard could simply drop into an ATX case.

DTX leaves space for 2 expansion slots on the motherboard. On early boards, these will probably be PCI-Express, or perhaps one PCI-Express x16 and one regular PCI slot. There has been talk of including an ExpressCard slot (as well as Mini PCI), but this may be more a suggestion than a requirement. Although AMD's reference designs are to be essentially free of "legacy" ports, manufacturers are free to include whatever ports suit them, just like ATX. If Asus thinks users will really want two serial ports, nothing is to stop them from including those ports.

While some press reports have suggested that an AMD processor is a requirement, this appears not to be the case. No particular socket requirement seems to be in place, and the only clear guideline for the processor is for Thermal Design Power (TDP). For DTX, a TDP of 65 Watts or less is suggested. For Mini-DTX, 35 W.

The demo system showed to the press had a laptop hard drive and a laptop optical drive, because they are smaller. It is not yet clear whether either will be a requirement, but it is unlikely. Current reports indicate that even the power supply is left completely at the discretion of the designer (no doubt to permit the use of very small power supplies, like those in Shuttle systems). The main connector from the ATX standard will probably be used.

Why Bother?

ATX certainly does not hold a monopoly on the form factor gig. Its derivatives, microATX and FlexATX, provide smaller options while maintaining quite good compatibility with more common ATX hardware. For even smaller systems, the Mini-ITX motherboard form factor (which only specifies the motherboard, not a full system) is also an option, as is the even smaller Nano-ITX. And more recently, BTX and its smaller variants have brought yet more variety to the mix. This leaves out entirely all the older or proprietary form factors.

If this sounds like a somewhat complicated situation (and an overcrowded market), well, it is. There are many "active" form factors a system designer might choose from, and yet the reality is that most are largely ignored. The very small form factors, especially, get very little love from motherboard makers. This has a lot to do with the strange dynamics of the Small Form Factor (SFF) market. It's not a very large market (yet), and it has historically been dominated by one brand: Shuttle. And Shuttle likes to use their own, proprietary form factor. But Shuttle has quietly shifted from selling do-it-yourself barebones kits to selling complete systems, and no one has really taken their place in selling mostly-standard small hardware. Even as the market expands.

So there may be a void to fill in small systems. But there are some other bits that have helped this introduction get more press coverage.

For one, DTX promises to cut costs a bit for motherboard manufacturers. All motherboards are manufactured starting from standard "blanks", PCBs (printed circuit boards) that have not been drilled or etched. These are etched, drilled, silkscreened, and cut to size. One of these blanks can be used to make two ATX motherboards, with a fair amount of leftover material going to waste. But it can make four DTX boards or six Mini-DTX boards, with less waste. To extremely cost-conscious motherboard manufacturers, this is a big deal. AMD thought it was such a big deal that four boards could be made from a single blank, they even brought along a board with four partially-complete motherboards on it to show the press.

Ulterior Motives

AMD has its own reasons for wanting this standard to take off, of course. Some are quite pragmatic. Others, less so.

Learning from the past

When Intel introduced the BTX form factor, it was struggling with cooling its increasingly power-hungry processors. BTX did some quite reasonable things to alleviate this problem, repositioning major system components. But notably, BTX is a relatively "strict" standard. Where ATX left many matters up to the discretion of product designers, BTX tended toward the specific. And one thing BTX spelled out was the location of memory modules.

This, too, was perfectly reasonable. But it created a problem for AMD. The entire family of AMD Athlon, Sempron, and Opteron processors have an integrated memory controller. And in order to work properly without a great deal of tweaking, they need all of the electrical traces connecting the processor to the memory modules to be roughly the same length. But BTX made this very difficult to achieve. If BTX had become widely popular, AMD would have eventually been forced to adopt it (or try to introduce a competing standard), which would have been quite a challenge.

Frustrated with the difficulties of potentially having to work with a standard into which the had no input (BTX was designed, formalized, and published by Intel), AMD took the proactive approach. With DTX, they could have their say.

Ankle biting

That issue of being completely left out of the process is no mere thing. After all, none of the form factors currently in use originated with AMD. ATX, BTX, and their variants are Intel designs. Mini-ITX is a VIA creation.

The moral victory possible by pushing aside Intel's ATX (especially following Intel's failed attempt to introduce BTX) would be significant. AMD, historically, is a company that likes moral victories. They like to prove they really can compete with a giant like Intel. And if they could succede with their own form factor so close on the heels on Intel's failed attempt to introduce one, in the process displacing another Intel form factor, that would be something.

Another BTX?

The public discussions of DTX have largely focused on how it compares to Intel's BTX. This is not altogether surprising, as BTX's failure still lingers in the air. To be sure, there are some similarities. Both standards very carefully consider how to evacuate heat from the case as efficiently as possible. Both attempt to preserve as much compatibility with ATX as possible.

But their goals are very different. BTX was an attempt to mitigate Intel's growing heat problem. DTX seeks more to cut down on wasted space inside the case and to capitalize on the advantages of low power processors. The design goals are very, very different. The philosophies are different as well. Where BTX was an unusually strict standard, DTX is unusually loose. Where BTX required a license fee paid to Intel, DTX is to be much cheaper or possibly free.

That is not to dismiss the possibility that DTX might share the fate of BTX. AMD has had trouble gathering support behind its Live! initiative, which may not bode well for DTX, which shares some major characteristics (a loose, maleable standard intended to be implemented by hardware and system manufacturers). Still, one never knows.

The DTX spec isn't even finished yet. Now is not the time to start writing its eulogy.

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