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 - Sunday, September 21, 2003 - link

    my thoughts are: only a retard could come up with this... Reply
  • Anonymous User - Sunday, September 21, 2003 - link

    #64 and #70. Like I said before, DUH, this is just NLX form factor again. I know because I am posting with it now. Go to IBM and look at 6862 model.

    Many of us are whining because it has been done before and INTEL will make make money, thru kickbacks or from changing the pinout so we'll have to buy a new motherboard. It'l' just be a COINCIDENCE that all the boards with the new pinouts are ONLY BTX. Intel will try to dictate that MOBO makers use the new factor or else their shipments of chips will be LATE. DUH!

    Don't think so, they did it before with AMD board makers, with DELL when they tried ATHLONS ....

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

    What a load of incredible hype & bull,
    I had to pinch myself & check if its April 1st
    or something.

    Not to mention its ugly.
  • Anonymous User - Saturday, September 20, 2003 - link

    biggest load of horse shite....what sort of idiots do Intel think we are?
    its a load of marketing ploys and money spinners!!
    long live ATX
  • Anonymous User - Saturday, September 20, 2003 - link

    Some fucking inovation...if you fellas remeber back to the Pentium 1 days, I had an Impression mobo with the CPU mounted on the bottom corner of the mobo _directly_ in front of the case fan!! This BTX shit only puts into the middle wtf? im sure you could snag a few degrees less by going back to the old style of things.

    One other concern...I beleive this is just intel trying make some more money by retiring something good for something new so people will have to go out and buy compatible components when they want to you recall that lame 12+ addon connector for P4, AMR, CNR...VLB/EISA bus from old 486 days?? wtf?? its nothing but a money making raquet.

    Fuck Intel.
  • DieHardware - Saturday, September 20, 2003 - link

    Thanks for the article Anand. I wish they had put the CPU a little further down and front for full/midtower cases(a la AT boards of old). Reply
  • Anonymous User - Saturday, September 20, 2003 - link

    Hmmmm. I feel we have a bit of a mixed bag here.

    The move from AGP to PCI Express is reasonable enough. With the cost of memory so low these days, the whole point of AGP is getting a little lost. Just wack lots of memory on the card itself. Wether the GPU manufacturers will end up doing that remains to be seen.

    On the other hand, I can't help feeling that this standard is just there to patch up some of the problems with the current ATX standard rather than looking toward the future. Unfortunately it's also more restrictive than ATX.

    My main issue with it is that (as someone pointed out earlier) there is no provision for SMP at all. This is a real limitation. With all of AMD's CPU offerings being SMP capable and Intel's Extreme Edition processors hinting that it too may soon embrace SMP on desktop systems, to release a new standard that doesn't support this does suggest that BTX may have a very short lifespan.

    Hopefully sometime soon we'll get a new standard that opens the way for better designs. The Apple G5 is a really good example of motherboard design, also the design of servers like IBM's X360. Unfortunatley BTX isn't it. ATX will have to exist alongside BTX until a new and better standard is devised.

    Overall I feel it's a stopgap design and possibly a missed oportunity.
  • idsanity - Saturday, September 20, 2003 - link

    oh no, $150 for 3 new cases! Why would you need 3 new cases unless you also plan to buy 3 new CPU's and BTX motherboards as well? If you have that kind of money to throw around, I don't see what the big deal is.

    As for the other comments, how can anyone assume Intel is doing this to make a few extra bucks? They don't get anything from BTX licensing. They won't make money off new cases. And if you want one of the next gen CPU's, you're going to need a new motherboard anyway.

    Sure, you may have an ATX setup that keeps everything cool now. But, Prescott and Tejas are going to be putting out a hell of a lot more heat and a redesign is absolutely necessary to accommodate this.

    As for the mirror image, it makes sense in that it will now put GPU's facing the cooling channel and it will prevent people from trying to put a BTX board in a case that isn't designed for the proper airflow needed to cool the new CPU's.

    And regarding the PCI Express x1 resembling CSA... sure, it kinda looks like it, but it offers 2x the bandwidth of current PCI. OK, but why not have a board with all PCI Express x16 slots... because there is no point. It would add unnecessary cost and PCI Express x1 already doubles what we have now with PCI.
  • Anonymous User - Saturday, September 20, 2003 - link

    a) according to BTX-spec we WILL have to buy new PSUs - it's using 24-pin conectors (not 20 as ATX)
    so I hope that's a typo in the article...

    b) the design IS better then ATX - if they can manage the cases to use only 3-4 fans in total it's great! (1 intake, 1 exaust were the i/o ports are + the PSU-fans)

    c) my CPU is in the mid 40's - that means the air leaving the heatsink is probably in the 30's - that air can cool very well, I bet my videocard is using hotter air right now

    d) the power-connector is placed were it should be (great!) but they SHOULD add s-ata-conections above/beside the RAM - the way it's now those cables have to cross the "windtunnel" outlined by the cooling-unit

    e) can't they use 120mm fans?!?
  • Anonymous User - Saturday, September 20, 2003 - link

    Let's see...I have 3 computers....$50 each for a new BTX case....Sure, I'll unnecessarily waste $150. I'm sorry but I have better things to spend that money on like rent, car payments, school, etc. Reply

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