Passively cooled graphics cards are both a blessing and a curse. On the one hand, they're silent, but on the other hand, they tend to be larger and more difficult to overclock than their HSF-equipped counterparts. The passively-cooled Asus EN7800GT TOP Silent is certainly larger than most 7800 GT cards, but it's also pre-overclocked, which potentially makes it a great product.
Asus has overclocked the GPU to 420MHz and the 256MB of GDDR3 RAM to 620MHz (1.24GHz effective). As a standard 7800 GT is clocked at 400MHz with 500MHz (1GHz effective) RAM, the EN7800GT is quite generously overclocked for a passively cooled graphics card.
The heatsink on the EN7800GT is far more cumbersome than any GPU cooler we've seen so far, as it relies not only on a large heatsink situated on the body of the card, but also on an additional radiator arm.
This is where the heatpipes dump any excess heat. The arm can be swivelled, but depending on which way the card is aligned, the arm should always be as close to vertical as possible, otherwise the heatpipes won't work efficiently. This isn't always the easiest thing in the world to do, since this radiator arm is beefy, and as most PCI-E slots are adjacent to the CPU socket, the arm has a real chance of smacking right into your CPU HSF.
For example, it's impossible to position the arm completely vertically in a PC with an Arctic Cooler Freezer series HSF, so after an hour of playing Need For Speed: Most Wanted, the EN7800GT overheated and we saw texture and geometry corruption. The EN7800GT's cooling mechanism is flawed: basically, it isn't possible to play games for even short periods of time if the radiator arm isn't fully vertical. It's tempting to just fold the arm downwards, where there's usually much more space, but the laws of thermodynamics mean that if you do this then you'll be lucky if the EN7800GT even makes it past the POST screen.
When working, the EN7800GT still has the performance power that we'd expect from a 7800 GT card. The frame rate in Battlefield 2, for instance, didn't drop below 32fps, and averaged 52fps at 1,600 x 1,200 with 4x AA and 8x AF.
F.E.A.R. is tough for a 7800 GT, and even pre-overclocked, the EN7800GT can only really give a playable frame rate at 1,280 x 960 with 2x AA and 2x AF. The story is much the same for Quake 4. This is at maximum settings, though, and both games still look amazing.
Overclocking a passively cooled graphics card tends to be unrewarding, as passive coolers struggle to deal with the extra heat. However, we managed to raise the GPU frequency to an impressive 475MHz, and the RAM to 650MHz (1.3GHz effective). This is a pretty sizable increase and yielded around a 5 per cent improvement to the frame rate. Clearly, if there's no conflict with your CPU HSF then the cooling system can be effective.
The problem with all passively cooled graphics cards is that the heat isn't actively vented out of the case. This means that to run the EN7800GT, you'll need to give some thought to how to keep your case's temperature low. A case without good airflow and at least a couple of reasonably powerful fans in operation will impede the effectiveness of the EN7800GT's cooling mechanism. This means that the EN7800GT isn't an ideal card for a completely silent PC. However, thanks to 120mm fans and fan controllers, there's no reason that your PC needs to be loud to have an effective air-cooling system.
CONCLUSION
Given that the reference coolers for 7800 GTs are so noisy, anything that can replace the noise with silence has to be a good thing. We were looking forward to seeing a passively cooled 7800 GT, but the EN7800GT is a flawed design. It isn't cheap either, and when you can buy a standard 7800 GT card and fit it with the very quiet Arctic Cooling VGA Silencer for £50 less, we have to conclude that the EN7800GT isn't worth the cost.
Author: Phil Hartup
Asus EN7800GT TOP Silent