PCB Design and Technical Characteristics

The GeForce 8800 Ultra seems to differ greatly from its precursor GeForce 8800 GTX, but it is only an outward appearance created by the modernized cooling system whose casing covers the entire card and makes it look massive. The card uses the same PCB design as the GeForce 8800 GTX, actually:

This is reasonable on the Nvidia part since developing a new PCB or modifying the old one would have required large money and time expenditures. Considering that the GeForce 8800 Ultra is based on a new-revision G80 chip with somewhat reduced power consumption, the use of the PCB from the GeForce 8800 GTX is justifiable. So, the two cards are absolutely identical save for the revisions of the GPU and NVIO chips.

Like the rest of the GeForce 8800 family, the GeForce 8800 Ultra is manufactured at Foxconn’s or Flextronics’ facilities and is shipped ready-made to Nvidia’s partners. The GeForce 8800 Ultra will be probably coming out with a black solder mask that endows the card with an exquisite and expensive appearance.

The snapshot shows that this is indeed the new A3 revision of the G80 chip. All other GeForce 8800 that we’ve ever dealt with in our labs carried revision A2 chips. Our sample of the GPU was manufactured on the seventh week of 2007, somewhere in mid-February. Besides a better frequency potential, the new revision features lowered power consumption. This is in fact the single difference in the end user’s eyes. The reduction of the power draw was not too urgent because the G80 looked modest against the ATI Radeon HD 2900 XT with the latter’s power consumption of 160W. Our measurements showed that neither of the three +12V channels of the GeForce 8800 GTX carried a load of higher than 43-45W. The reduced power draw will help the GeForce 8800 Ultra keep within the predecessor’s limits despite the increased clock rates.

The GPU being the same, its configuration hasn’t changed, either. The A3 revision G80 chip incorporates 128 unified stream processors capable of executing any type of shaders, 32 TMUs with one address unit and two filters units per each, and 24 raster operators.

According to the ordering code on the box, our sample of XFX GeForce 8800 Ultra belongs to the XXX series that has the highest clock rates of all the versions of the Ultra offered by XFX, but the card’s real frequencies differ from what the manufacturer website declares. The GPU core frequency is 648MHz as opposed to the specified 675MHz while the shader processor frequency is 1620MHz as opposed to the specified 1667MHz. These numbers are in between the XXX and Extreme versions, the latter having officially specified GPU frequencies of 650/1605MHz.

We have an official explanation of this discrepancy from XFX. Our test lab received an early sample of XFX GeForce 8800 Ultra XXX clocked at frequencies that correspond to the current version of XFX GeForce 8800 Ultra Extreme. Thanks to a careful selection of cards the company could make the XXX and Extreme series operate at higher frequencies than had been planned originally and our sample is in fact an XFX GeForce 8800 Ultra Extreme rather than an XXX. We should note that the card would heat up greatly even at 648/1620MHz and its cooler could hardly cope with it in the summer heat. According to RivaTuner, the GPU temperature was never lower than 90°C under load.

A more interesting point of difference is that the PCB carries unique memory, Samsung K4J52324QE-BJ08. This memory is not yet even mentioned on the manufacturer’s website. According to the official documentation, the fastest chip in this series is suffixed “BJ1A” and works at a frequency of 1000 (2000) MHz and 1.0V voltage. So, these are completely new chips with an access time of 0.8 nanoseconds and capable of working at a frequency of 1250 (2500) MHz. It is the first time GDDR3 memory has such speed characteristics that have hitherto been available with GDDR4 chips only. Such chips cannot be cheap and the GeForce 8800 Ultra must owe its high cost to this very factor largely.

The memory chips do not work at their rated frequency on the GeForce 8800 Ultra. This may be the reason why their voltage is lowered, probably from 1.9V to 1.8V. The lower voltage leads to lower power consumption, too. The chips are clocked at 1134 (2268) MHz, which roughly corresponds to the specified memory frequency of the XFX GeForce 8800 Ultra XXX, 2.3GHz. With a 384-bit memory bus this frequency ensures a bandwidth of 108.8GB/s, somewhat higher than the memory bandwidth of the Radeon HD 2900 XT that has a 512-bit bus but a much lower memory frequency. The total amount of graphics memory on board the GeForce 8800 Ultra is 768MB, just like on the GeForce 8800 GTX.