Board analysis

The 7900 GT and X1800 XL

GeForce 7900 GTX

Can you spot the 7900 GTX board? It is at the bottom

If you’re familiar with the board design of the GeForce 7800 GTX 512MB, NVIDIA’s GeForce 7900 GTX should look very familiar to you. That’s because NVIDIA’s using the exact same PCB, and has only made a few minute changes to the board’s design. Looking over the two reference boards side-by-side, you’d hardly notice a difference between the two cards, but there are a few subtle differences. Let’s quickly go over the basics first.

The most striking aspect of the GeForce 7900 GTX is its cooler. NVIDIA uses a large, dual-slot heatsink/fan combo to keep the 7900 GTX’s G71 graphics core and memory cool. This cooler was first used by NVIDIA on their Quadro FX 4500 cards and does a very good job of keeping the graphics core cool. In fact, we witnessed load temperatures in the 50-degree Celsius range during our testing in an open-air environment. Only when running in SLI mode did we see temperatures that approached GeForce 7800 GTX levels, and this was only on the primary graphics card (as the secondary card sits below the primary card and has a fresh supply of cool air to keep the card’s fan fed).

NVIDIA uses a combination of a copper base plate (which rests directly over the GPU) with a large aluminum heatsink, and four heat pipes to transfer heat off the GPU and memory modules. Topping it all off is a large fan, which supplies the cooler unit with the air from within your case. The fan itself is quite large, in fact it’s slightly larger than the 80mm case fans many of you are probably using in your system’s case right now. Fortunately though it doesn’t run loud, in fact it’s practically silent in use, even when overclocking. The fan sucks in the air from within your case, using it to help keep everything cool. From there the air from the fan passes out both sides of the heatsink, including outside your system case.

GeForce 7900 GT is shorter than 7800 GT/GTX

GeForce 7900 GTX back plate

The 7900 GTX

One key difference between the board design of the new 7900 cards in comparison to the 7800s is their new 7-pin HDTV-out mini-din connector. According to NVIDIA, with the new 7-pin min-din connector, you can plug an S-Video cable directly into the connector, or use a dongle for component or composite connections. With the old 9-pin connector used on previous GeForce cards required a dongle to use S-Video, component, and composite outputs.

In terms of power requirements, NVIDIA’s guidelines are pretty similar for the GeForce 7900 series as they were for the 7800s. NVIDIA recommend a 350W-400W power supply (22-26A on the 12V rail) for the GeForce 7900 GTX, while a 300W-350W power supply is recommend for the 7800 GT (20-23A on the 12V rail). For SLI rigs NVIDIA is even more specific:

Ultra High-End SLI PC
You must have a power supply that can provide a minimum of +12V @ 22A of dedicated power for the two graphics cards. Of this 22A requirement, +12V @ 5.5A must be available to each of the two PCI Express 6-pin auxiliary power supply connectors. The remaining 11A must be supplied to the motherboard for dedicated graphics card use.

High-End SLI PC*:
Minimum of 500-600W Power Supply with a minimum of +12V @ 30A for all PC components.
Mid-Range SLI PC*:
Minimum of 450-500W Power Supply with a minimum of +12V @ 26A for all PC components.
Low-End SLI PC*:
Minimum of 400-450W Power Supply with a minimum of +12V @ 22A for all PC components.

Just to provide a frame of reference, NVIDIA’s “mid-range SLI PC” consists of an Athlon 64 4000+ with one hard drive, an nForce4 SLI motherboard with 1GB RAM, two optical drives, and one PCI sound card, while the “high-end SLI PC” contained an FX-57 CPU, nForce4 X16 SLI motherboard with 2GB RAM, two hard drives running RAID 0, two optical drives, and a PCI sound card. Needless to say that the power requirements for the 7900 GT/7900 GTX aren’t anything extraordinary for your typical hardware enthusiast nowadays.

GeForce 7900 GT board

Back of the 7900 GT card

The 7900 GT board

Since it runs at considerably lower clocks than the 7900 GTX, the 7900 GT gets by with a simple single-slot copper cooler. In fact, this is the smallest heatsink/fan unit NVIDIA’s used on a high-end card since the GeForce4 Ti 4600 over four years ago. The PCB itself is smaller than the GeForce 7800 GTX 256MB PCB as well, in fact it’s even shorter than the GeForce 7800 GT’s PCB. Due to this fact, and the board’s lower operating temperatures (and noise levels in comparison to the 7800 GTX 256MB), we’d feel very comfortable putting the GeForce 7900 GT in a SFF system. In fact, the GeForce 7900 GT has even sweeter SFF potential than the GeForce 6800 GT or Radeon X800 XL because of this.