The Board

Now that we’ve seen the NV43 chip we'll take a look at the details of the reference NVIDIA 6600 GT AGP platform and how it configures the chip and memory:

As we can see from the main board specifications, and comparing them to the PCI Express 6600 GT, the core speed of 500MHz remains the same on both, as does the 128MB frame-buffer size, however the memory speed on the AGP version has been dropped by 50MHz, thus reducing the local memory bandwidth available. Of course, the other difference between the two boards is that the newer one operates on the older AGP interface.

What is clearly most obvious about the 6600 GT AGP board is the odd angle and the heastsink, and memory underneath it, sits at – this is, of course, in order to facilitate the HSI bridge chip, whose own passive heatsink can be seen below the main core heatsink. With the 6800 series NVIDIA have integrated the HSI bridge chip on to the package of the core, however with this part utilising a 256-bit memory bus the layout of the board is a little more critical, but on top of that, dual chip packaging is costly. While costs aren’t quite as much of a concern on high priced enthusiast boards, in the mainstream they become much more critical, hence a discrete HSI chip and package is used on the 6600 GT AGP board.

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Because the traces from the interfaces to the bridge device need to be kept in fairly close proximity, this means that there are few places to effectively locate the core from the bridge device. With the PCX 5950 NVIDIA moved the core around 90° clockwise, however on this board the chip is rotated by about 45°, anti-clockwise, towards the front of the board. The positioning of the core on the 600 GT AGP has advantages over the PCX 5950 in that the board size remains about the same as the PCI Express 6600 GT, and also the traces for the display output from the chip to the actual plugs wont be as long, nor routed past any other high frequency devices.

The test board features the same 2ns Samsung GDDR3 RAM as the PCI Express 6600 GT did, although, as mentioned, its running at 50MHz lower frequency. The board also has a Hard Drive power connector input as the AGP bus is able to provide less power as the PCI Express interface can, and this board also has to power the HSI chip which the PCI Express board doesn’t. The test board also features two DVI outputs, but no Video-In chip that was on the PCIe version – presumably these will be options for board vendors to pick and choose whether to include.