X-bit labs

XFX GeForce 7600 GT XXX Edition Graphics Card Review (page 2)

Category: Video

by Alexey Stepin

[ 07/27/2006 | 11:49 AM ]

Nvidia G73: Specification

Like the G71, the G73 chip is manufactured on TSMC’s 0.09-micron tech process with low-k dielectrics, consists of 177 million transistors, uses a 128-bit GDDR3 memory interface, and has 12 pixel and 5 vertex processors. In other words, it has the same number of functional subunits as the NV42, but has less transistors and a different memory controller.

If you compare the GeForce 7600 GT with its direct market rival Radeon X1800 GTO, you’ll see that the G73 has a much lower transistor count: 177 million against 320 million in the R520 with some subunits disabled. It means that Nvidia’s graphics processor costs much less to produce.

The 128-bit memory access might provoke some apprehensions, yet it doesn’t necessarily mean a failure in competition with the opponent as has been confirmed in our earlier tests (see our article called PowerColor Radeon X1800 GTO Graphics Card: the Best in Its Class?), and this narrow memory bus simplifies the design and wiring of the graphics card’s PCB to a great extent. So, G73-based products are cheaper to manufacturer, and Nvidia has quite a lot of room for price maneuvering. ATI Technologies uses a PCB initially designed for high-performance and expensive solutions for Radeon X1800 GTO (as well as for Radeon X1900 GT), so the Canadian firm doesn’t have much freedom in setting the price for this product.

The GeForce 7600 GT also has fewer raster operators (ROPs) than the Radeon X1800 GTO. Combined with the narrower memory bus, this will negatively affect the performance of the card in certain cases, particularly in high display resolutions and when full-screen antialiasing is enabled. But these cards being mainstream solutions, this rarely becomes a real problem since their performance is often not high enough for comfortable play if you try to use high resolutions and FSAA simultaneously.

The difference in the number of vertex processors doesn’t matter much, either, because the scene geometry in modern games isn’t yet as complex as to make this factor crucial.

A curious fact, the GeForce 7600 GT is declared to have 12 pixel processors, but RivaTuner reports there are 16 of them in the G73, but one quad is disabled on the hardware level.

As you see, Pixel Unit 2 is disabled, i.e. only 12 out of the 16 pixel shader processors are active. We are not sure if the extra pixel processors are an error of the program, or a means to increase the chip yield by increasing the number of execution subunits, or a strategic reserve against future opponents. According to Nvidia, the chip contains 177 million transistors and works at a rather low clock rate, so we doubt the company would put spare execution subunits into it since this redundancy isn’t observed in more complex chips that work at higher frequencies. On the other hand, if there are really extra pixel processors inside, Nvidia has prepared a simple means to respond to ATI Technologies’ launching a new high-performing mainstream solution.

We will be examining XFX’s version of the GeForce 7600 GT today. It is called XFX GeForce 7600 GT XXX Edition and has improved clock rates, but its design is exactly the same as that of the reference card.