The boards

With SLi all the rage these days, reference boards from Nvidia these days come as identical twins. The 7800 GTX has a few obvious talking points, so if you want to pull up a chair and have a good look at one on its own, I'll give you the grand tour.

Longer than a 256MB 6800 Ultra or 6800 GT, the PCB for the 7800 GTX isn't small. I'd say it's just shorter than the 512MB 6800 Ultra that various vendors have been peddling in recent times. The single-slot aluminium reference cooler causes the board to weigh in at around the same 320g as a reference 6800 GT, and a fair bit less than a reference 6800 Ultra.

Single-slot is one of the key indicators to a faster flagship product, probably labelled Ultra, which will likely sport a dual-slot cooler. The cooler hides the dual-link TMDS that drives the first of two DVI ports. The dual-link TMDS can drive larger digital displays than the single-link (1600 x 1200) DVI links on almost all other Nvidia boards made to date. Indeed, the panel that the linked Ultra DDL was designed to drive is one such beast that the 7800 GTX can make light work of.

Nvidia uses digital VRMs for power management this time - there are barely three capacitors on the entire product. A black aluminium heatsink cools a FET bank whos high switching speeds equals heat to manage. Being PCI Express, there's approx. 75W available from the slot (see the first few pins on the connector? they're for power) with a six-pin power connector giving the board the rest.

The rear of the board shows you how the GPU is positioned centrally with its heatsink retained by a fairly sizeable bracket. Another bracket, L-shaped, covers the rear memory modules and double up as a retention mechanism for the rest of the cooler. Exposed, you can see four of the eight GC16, 600MHz (1200MHz DDR) Samsung GDDR3 DRAMs that have been ubiquitous on high-end graphics hardware for the last 14 months. They're the same chips that powered 6800 Ultra.

With four DRAMs on the front of the PCB and four on the back, and with obvious room for eight more, 512MB boards - or 1GB should Nvidia prise double-density DRAMs from Samsung's mitts - should show up in due course.

It seems to have a 1.25V Vcore voltage for the 430MHz core clock, and going by the lack of noise the cooler makes under all but the heaviest of loads, it doesn't get too hot. That's not to say that at full chat they aren't loud - they really are, and with two on the go for SLi you definitely hear the noise they make - it's just that the temperature-controlled fans didn't seem to hit full chat all that often. As always, your chassis cooling helps immensely in that respect.

Power-wise, Nvidia will tell you that a single board draws 100W under load and two boards in tandem need 220W. That's pretty close to the mark, with my calculations showing an extra 80W or so of output power consumed when you add in a second board.

Nvidia claims that a 500W power supply is needed for SLi. That's an overstatement, designed to protect it from craptastic supplies that can't supply the output power an SLi system needs. If there's any more than a 300W output power from a high-end SLi rig with GTXs (without loading it up with disks), I'll be very surprised. 100W is less than 9A from a 12V source. Any decent ATX or ATX 2.0 can pull 18A with room to spare for the CPU, and with ATX 2.0 you've got that from an independent voltage rail. Just make sure your power supply is from a decent, trusted vendor, and you'll be fine. I used a Tagan TG480-U01 during all my testing, including SLi and with the most powerful x86 processor on the planet, without any issues.

Next page: Test Hardware

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