Nvidia GeForce 7900 GTX

PCB Design

The senior model of the new family, GeForce 7900 GTX, uses the same PCB design as the GeForce 7800 GTX 512:

The two graphics cards have the same appearance and are equipped with identical coolers. You can only spot a few differences on the reverse side of the PCB unless you remove the cooler: a few chips and small elements are missing on the GeForce 7900 GTX near the power connector. They used to be part of the power circuit, obviously. When the cooler is removed, the much smaller GPU die and the empty seat previously occupied by a VIVO-supporting Philips SAA715HL chip catch your eyes. On a closer inspection, you can also note that some elements of the power circuit are missing here but were present on the GeForce 7800 GTX 512. This again proves that the G71 has lower power requirements than the G70 clocked at 550MHz.

There’s a huge difference between the die area of the G70 and G71 chips. The core of the new chip is almost 1.5 times smaller than of the older one. Even the thinner, 0.09-micron tech process couldn’t have helped to do that hadn’t Nvidia optimized the new GPU and made it slimmer by 24 million transistors. The G71 sample on our graphics card was manufactured on the 6th week of 2006, i.e. from February 6 to 12 or near two months ago. This is the third, A2 revision of the chip (counting from A0).

There is no protective frame around the die, although the smaller die is easier to damage. Nvidia’s cooling system isn’t too heavy, however, so the GPU will come to no harm if you handle the device carefully enough. Exactly complying with the specification, the graphics processor works at 650MHz. This frequency is the clock rate of the pixel processors and raster operators whereas the vertex processors of the GeForce 7900 GTX work at a higher clock rate of 700MHz.

Like the GeForce 7800 GTX 512, the GeForce 7900 GTX uses graphics memory from Samsung’s K4J52324QC series in the modern 136-pin FBGA packaging. The BJ-11 prefix indicates that the chips work at 2.0V voltage and have an access time of 1.1 nanoseconds which means operating frequencies up to 900 (1800) MHz. Each chip has a capacity of 512Mb and is organized as 16Mbx32, so eight such chips suffice to provide 512 megabytes of memory with a 256-bit memory bus. The memory is clocked at 800 (1600) MHz while the memory of the GeForce 7800 GTX 512 worked at 850 (1700) MHz. Thus, the peak memory bandwidth of the new card is lower in comparison with the previous model: 51.2GB/s against 54.4GB/s.