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BTX: The Next Form Factor Standard?

Over the past year, Intel has been pressing forward with BTX (balanced technology extended) in an attempt to make it the next universal form factor for motherboards. Certainly Intel’s past success with the ATX standard bodes well for BTX, but the company isn’t quite as dominant as it was back when ATX appeared. We’ve heard of discontent among PC chassis and motherboard suppliers in Taiwan, as well of rumblings that Athlon 64 BTX motherboards may not be forthcoming. The tea leaves are a bit more roiled this time around, and predicting universal success for BTX is no sure thing.

Still, BTX will be Intel’s primary form factor, and the Santa Clara, Calif. company still has the dominant market share in processors, so the sheer volume of products will ensure at least some success for it. We’ve written about the early gestation of BTX, back when it was called Big Water and its eventual evolution to the BTX motherboard standard. Here’s a brief refresher:

When Intel was confident about hitting 5GHz for its processor line, system designers were concerned about the amount of heat generated by increasingly high-clock-rate components. The CPU was the major issue, but graphics cards were getting hotter, as were other system components. So Intel engineers felt that a new form factor was in order–one that improved cooling efficiency while managing noise levels. The end result was BTX.

In fact, Gateway has been shipping BTX systems for several months now. The ingredients to “roll your own” have been absent, as we’ve seen no retail BTX motherboards or cases in the channel. Intel is hoping this will change in the near future. To facilitate awareness, the company shipped BTX evaluation kits to the media. We took their kit and built a PC with it so that we could see how it might work.

The one downside of this kit is that it’s a low-profile system, built around a MicroBTX motherboard. It’s not exactly a performance enthusiast’s dream machine, but working with the system gave us some idea of what to expect. The BTX standard is flexible enough to allow for “PicoBTX” systems as small as or smaller than Shuttle XPC cube systems. The standard also accommodates larger motherboards built into BTX tower cases for people who need maximum expansion or performance.

So let’s take a trip down BTX lane and see exactly how it all goes together.

Let’s take a look at the components we’ll be using to build the system:

  • Intel D915GMH MicroBTX motherboard, Intel 915G chipset
  • AOpen B300A MicroBTX chassis with a 275W BTX power supply
  • Intel Pentium 4 model 550 processor w/BTX thermal module
  • ATI X700 Pro PCI Express graphics card
  • 512MB Kingston HyperX DDR400 memory (2 x 256MB modules)
  • Seagate 120GB Serial ATA hard drive
  • Sony DVD-ROM drive with black faceplate

As it turns out, the AOpen B300A is a low-profile case, which means you can’t pop in full-height cards. However, it does ship with a PCI Express riser card, allowing you to install a full height PCI Express graphics card. For reasons we’ll discuss shortly, we ended up using an ATI X700 Pro PCIe card.

The Intel D915GMH uses standard DDR400, rather than DDR2, which is a curious choice for an evaluation platform, given Intel’s push towards DDR2. Since the case doesn’t support full-height PCI cards, we couldn’t install a PCI sound card, so we went with the integrated Intel HD audio.

AOpen B300A Case

The AOpen B300A is about the size of two large pizza boxes stacked on top of each other:

The BTX standard allows for a flexible design in the I/O back plate:

When you open up the case, you’re greeted with what looks like typical sheet metal. This version of the B300A does have rough metal edges in some places, so you can cut your hand if you’re careless.

The BTX thermal module retention plate is installed under the main motherboard section. In addition to mounting the thermal module, it can bleed away some additional heat.

The fan intake is in the front of the case. A soft rubber surround is attached to the metal, and a foam air filter prevents dust from being sucked into the case interior.

The power supply and optical drive bay flip out, after you remove three screws, easing access to the hard drive bay:

The bottom line is that the B300A is a somewhat average case, but does have a few features to help system building. For all its compact size, it’s a heavy little thing.

The Intel D915GMH is a MicroBTX motherboard, with two PCI slots, one PCI Express x1 slot and a PCI Express x16 graphics slot. If you don’t want to populate the PCIe x16 slot, you can opt to use the integrated Intel Graphics Media Accelerator feature.

The BTX standard doesn’t define any new methods for mounting the motherboard into the chassis. In the case of the B300A, screws and metal standoffs are used, similar to ATX cases.

Let’s turn our attention to the thermal module. Our kit arrived with the processor and thermal module encased in plastic, similar to what you’ll find inside a retail processor package.

Note that we’ve been using the phrase thermal module instead of heat sink. In fact, the lowly processor-cooling fan has evolved into a system-cooling module. Just how big is the new thermal module? Let’s take a look at it alongside a typical socket 478 HSF.

The new thermal module weighs in at 2.75 pounds. That’s right, it’s two pounds and twelve ounces, or 1.25 kilograms. That’s a lot of copper and aluminum. This is the high end of the Intel reference design. The next spin of the 550, and lower-clocked CPUs, will get a lighter weight and possibly smaller module.

Let’s take another look at the motherboard, from a different angle, prior to installing the thermal module:

The thermal module mounts with four screws, which attach to anchors on the thermal module retention bracket. Two of the mounting points lie under the motherboard, while two are in front of the motherboard. Now let’s look at the system with the thermal module installed.

Although more massive than most CPU coolers, the BTX thermal module doesn’t merely cool the CPU. It draws in cool ambient air and uses it to cool the processor, the north bridge and–as we’ll see shortly–the graphics card.

Since we do play the occasional PC game, we try to avoid using Intel’s integrated graphics. While the GMA 900 is much improved over past Intel efforts, it doesn’t begin to approach the performance of even modest dedicated graphics cards.

The AOpen B300A is a compact case that doesn’t accommodate full-height cards. However, the case does ship with a PCI Express riser card. This serves two purposes: First, it lets you install a larger graphics card than otherwise possible. Second, it places the GPU in the path of the main system airflow generated by the BTX thermal module.

But another constraint exists: The maximum length of the card is limited by the distance from the rear of the thermal module to the back edge of the case. In other words, forget about installing a long card, such as a GeForce 6800GT. And a “double wide” card is simply hopeless. Even a slightly shorter card, such as ATI’s X800 series, won’t fit.

However, ATI did send us a Radeon X700 Pro card. This card clocks slightly slower than the X700 XT we reviewed a few weeks ago, but it’s still a capable card with 8 pixel pipelines, and it supports Microsoft’s Shader Model 2.0b. Better yet, the card is just short enough to fit.

First, we need to install the PCI Express riser card into the system:

Next, we carefully insert the X700 Pro into the PCI Express riser card. Only about a quarter-inch clearance lies between the back edge of the card and the thermal module:

It’s uncertain what effect the GPU active cooler will have, as it circulates air at right angles to the airflow of the BTX module. Most BTX block diagrams tend to show passive coolers mounted on video cards. We’re starting to see graphics cards with exhaust vents, and we may see future high-end GPUs with active coolers whose airflow merges with the BTX cooling unit airflow.

We mentioned the awkward location of the 24-pin power supply and front-panel USB connectors. These need to be connected before installing the graphics card. They also lie directly underneath the GPU, and the thick cabling only serves to block the airflow from the thermal module. It would be best if these necessary cable connections were built onto the motherboard outside of the critical main airflow.

Installing mass storage is pretty simple. The hard drive and optical drive bays use tool-less mounts, so you don’t need to screw in the drives. You can see how it works by looking at the 3.5-inch bay:

Once storage is in place, we buttoned up the case:

We then fired up the system and installed Windows XP Pro. The whole affair behaved much like other compact 915G systems we’ve tested. The system was noticeably quieter than the cube-shaped small form factor PCs in our lab, but not as quiet as the average Dell desktop PC. On the other hand, a little time spent properly dressing the cables would have quieted things a bit more. This system was built with what will become stock parts, without any special attention paid to special quieting options, such as rubber drive grommets or extra-quiet, 12cm fans.

BTX’s success isn’t completely assured, but we’re certainly encouraged by what we see. We look forward to checking out high-performance BTX systems and even tinier small form factors. Until then, we give BTX a cautious thumbs up, based on one system and one case. This is still beta hardware, though. If production samples perform as well, then BTX will likely become a check box item for system builders in the future.