Design and Specifications

The GeForce 9800 GX2 features a very complex design, and it’s no wonder that the new graphics card is covered by Nvidia’s no-modifications prohibition. Unique single-PCB versions of this graphics card may come out in the future, though. For example, we expect ASUS to attempt such an experiment. But right now, all versions of GeForce 9800 GX2, including the described product from Zotac, are copies of the reference card.

As opposed to the Nvidia GeForce 7950 GX2, the PCBs of the GeForce 9800 GX2 face each other and allow using a common heatsink for both graphics cores. The PCBs are about 27 centimeters long, the GeForce 9800 GX2 having roughly the same dimensions as the GeForce 8800 GTX/Ultra. The cooler’s fan is located between the PCBs, and there is a figured hole in each of them fir air intake. The bottom PCB, equipped with a PCI Express x16 connector, carries a PCI Express switch. The PCBs are fastened together with metallic poles and connected with two flexible cables.

Each PCB is equipped with a three-phase GPU power circuit governed by a Volterra VT1165MF controller and a memory power circuit based on an Intersil ISL6269CRZ. The bottom PCB has a standard 6-pin PCI Express 1.0 connector while the top one is equipped with an 8-pin PCI Express 2.0 connector. The card doesn’t start up if you plug a 6-pin power cable into the latter connector, reporting a power error. Nvidia took this precaution because the top PCB cannot access the PCI Express x16 slot and is powered only from the external connector while the power consumption of the components it carries is surely above 75W. Well, you can also use the included adapter (2x6-pin PCI Express → 1x8-pin PCI Express) to power the card up. This is safe electronically because the splitting of the PSU’s +12V power rail into multiple output lines is only done to limit the current in order to comply with safety regulations, and six pins is quite enough for a current of about 8A. This is the load of the top PCB of the GeForce 9800 GX2 by our estimates. The power connectors are placed rather inconveniently: the connector locks press against each other, and you have to use a screwdriver to take them out. Moreover, the narrow slits in the casing make it impossible to plug in connectors with large locks. An SPDIF connector is located nearby.

The GPUs of the Zotac GeForce 9800 GX2 have a standard configuration with 128 ALUs, 32 (64) TMUs and 16 ROPs. The frequencies are standard: 600MHz for the main domain and 1500MHz for the shader domain. Nvidia doesn’t allow overclocking the GeForce 9800 GX2 even at the factory, obviously due to high heat dissipation. Each PCB carries eight GDDR3 chips (Samsung K4J52324QE-BJ1A) with a rated frequency of 1000 (2000) MHz. That’s indeed the frequency the chips are clocked at by the card. 3D application can access 512 megabytes of memory, so the mention of 1024 megabytes is just a marketing trick.

The Zotac GeForce 9800 GX2 has the same interfaces as the reference card: two dual-link DVI-I ports and one HDMI port. There are two LEDs there, one of which reports that the card is powered properly and the other marks the Master DVI port in Quad SLI mode. To configure the latter mode, the card offers a MIO connector for connecting to another GeForce 9800 GX2. As we noted earlier, the card supports multi-monitor configuration only if SLI is disabled.

The cooling system is simple and consists of a heatsink between the PCBs – it has contact with the GPU dies via copper soles. Most of the card’s mounting bracket is populated with interface connectors, and most of the hot air is exhausted into the system case through the slits in the cooler’s casing. The small opening in the bracket seems to serve an aesthetic purpose as it is highlighted with bright green LEDs. The airflow through this hole is very weak.

The cooler is almost silent in 2D mode, but the fan speed is increased greatly under load and there is more noise then. The card becomes perfectly audible even in a closed system case. We guess the ATI Radeon HD 2900 XT is the only modern graphics card that has a nosier reference cooler. So, this cooler does its job all right, but at the expense of the user’s acoustic comfort.