BTX - The Basics

Just in case you were told otherwise, the BTX form factor is largely incompatible with the ATX form factor - the only area where this doesn't fully apply is in power supply support, as you can use ATX power supplies with BTX motherboards (more on this later).

In order to understand BTX you have to understand the motives for change. CPUs are getting hotter, graphics cards are as well, and despite all of these increases in thermal dissipation there is an increase in demand for quieter PCs. Today's ATX cases and motherboards were not designed for the incredible levels of heat that they have to deal with, and it is with this that we begin our understanding of BTX.

Pictured below you will see a BTX motherboard reference design:

The first thing that you'll notice about the BTX form factor is that the expansion slots have switched sides. In the picture above you'll see a total of 7 slots, from left to right we have a PCI Express x16 slot, two PCI Express x1 slots and four 32-bit PCI slots. Note that the slot closest to the CPU is the PCI Express x16 slot, which will be used for graphics, allowing it to share some of the CPU's cooling.

The redesign of the board layout was done in order to improve airflow through the system; moving the CPU to the "front" of the case allows it to be right next to the intake fan, giving it the coolest air out of any component in the system. You will then notice that the chipset is directly in line with the CPU, allowing airflow over the CPU's heatsink to be channeled over those heatsinks as well before exiting the case. This direct line of airflow allows for very efficient cooling of not only the CPU, but the voltage regulators, chipset and graphics card.

The memory slots have been moved to the left edge of the motherboard, but are also able to receive cooling courtesy of the thermal module, as it is known, that is mounted over the CPU. You can see a good example of what the thermal module will look like below:

The white plastic duct encloses what is known as the "thermal module," which at this point is basically a heatsink and a fan. In the future, the thermal module could encapsulate some more exotic cooling forms such as heatpipes or potentially even water cooling. In this particular design, the fan seen above is a 90mm unit.

In order to understand the cooling flow within a BTX system, take a look at the picture below:

In the depiction above the graphics card is mounted on a riser card, although it can also be mounted vertically.

Index Three Different BTX Sizes


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  • Anonymous User - Saturday, September 20, 2003 - link

    Lets see here. Take the cool air and cool the hottest thing in the case, the cpu. Then use that same air which is now 50 to 60 degrees C to cool other parts of the computer. D-oh.
    Excuse me but not much cooling will take place if the coolant is 50 to 60 degrees C. What idiot thought that up.

    Sorry but this really sucks. I'm sitting here looking at my 5 computers knowing that when its time to upgrade the motherboard the case will have to be upgraded as well.
  • Anonymous User - Saturday, September 20, 2003 - link

    #64, It's not that the evoluionary improvements aren't good enough, it's that almost all these improvements could be implemented on an ATX board with just a small rearrangement of components. Some Asus boards already do some of these changes by moving the memory to the top of the motherboard and putting the CPU and northbridge in line with each other (P4T-series). And if the GPU could be fliped to the back side of the card, like they sometimes do with RAM on graphics cards, that problem would be solved too. And if not, just leave the PCI slot next to the AGP empty, like most people do. No problem.

    All these changes on an ATX board would be nearly as effective as BTX and would allow us to still use our ATX cases. That's the major argument that nearly everyone here is getting at. And it's an incredibly valid argument. So what if a new BTX case would cost me an additional $50. That's $50 I could put towards a better CPU, RAM, motherboard, or simply in my pocket.
  • Anonymous User - Saturday, September 20, 2003 - link

    i also like the solution that apple came up with. i would prefer to see something more like that instead. Reply
  • Anonymous User - Saturday, September 20, 2003 - link

    Man you guys are a tough room. Whine whine whine...not innovative enough...whine whine whine...Intel is trying to control the world...whine whine whine...cooling the CPU first is no good...whine whine whine...BTX is crap.

    Geez...please explain to me how ATX does a better job at *any* of the things you are trashing BTX over. Sure, BTX is going to blow warm air over your northbridge. ATX doesn't blow *ANY* air over your northbridge, but that's okay apparently. BTX will blow hot air over your video card. Once again, ATX doesn't try to blow ANY air over your video card, and in addition flips the video card upside down to trap the hot air underneath, but it gets a pass on this as well. Yet BTX is criticized, apparently because it doesn't create a hyperdimensional space-time warp in your case, allowing *all* the components to be the first one in front of the intake fan simultaneously. Someone said they should concentrate on adding more active cooling to the ATX spec. Great idea...just what we need, even more fans in our PC's. This is EXACTLY what they were trying to reduce (of course it remains to be seen if BTX will be effective in this area).

    Secondly, as for the charge of not being innovative, so? Evolutionary improvements aren't good enough for you? Does it have to have antigravity or something before you'll allow it in your house?

    Third, nobody is going to be forced to buy BTX. There is no magic pixie dust in the PCI Express or SATA spec that prevents it from being implemented on an ATX motherboard. I predict we will see many, many ATX PCI Express motherboards released. And even if BTX does take over the world some day, so what? You'll have to buy a new $50 case 5 years from now when the last ATX motherboard is discontinued and you want to upgrade. Big deal. All your cards and drives and so on will work just the same in a BTX motherboard.

    I'm not saying BTX is great (the jury is still out), but at least it tries to address some of the problems with ATX, and for that it gets trashed by people almost reflexively because they don't like Intel (neither do I particularly, but I like to withold judgement until we actually can see some real systems in action).
  • Anonymous User - Saturday, September 20, 2003 - link

    BTX = Broken Technology eXtended Reply
  • Anonymous User - Saturday, September 20, 2003 - link

    am i the only one who is reminded of 1980s style mobos, with the RISER cards?

    retro != innovation.
  • Anonymous User - Friday, September 19, 2003 - link

    This is rubbish.

    Why not just build motherboards with all the IO and video built in, and then use the slots to plug in CPU + RAM boards. (Opteron + 4 DDR ports per plug in board). Opteron hypertransport and built in memory controller should make this relatively trivial.

    Id buy that.

    Real innovation - retro style - would be to build the motherboard as a backplane switch like the (old) SGI Octane XBow board - plug in as many IO modules or CPU modules as you like, and have the backplane deliver guarnateed enormous bandwidth between disparate elements.

    PeeCees still suck.
  • Anonymous User - Friday, September 19, 2003 - link

    Intel's to do list:
    1. change ATX into BTX through the use of mirror technology
    b. change AGP to PCI-Express 16
    III. change change some PCI to PCI-Express
    D. move the processor to the lower front of the case
    - sell everyone a new computer that opens on the side opposite what everyone in the last 20 years has gotten used to

    P.S. somewhere in there, insert profit
  • Anonymous User - Friday, September 19, 2003 - link

    Only 7 slots in the reference case? No offence, but unless you are using only micro BTX boards, you WILL run out of slots space not by stupid expansion cards that wastes slot spaces with connector brackets. Reply
  • Anonymous User - Friday, September 19, 2003 - link

    Isn't BTX the comic[1] written by the same guy that did Saint Seiya?


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