The radiator covers both the graphprocessor and a PCIe to AGP bridge. There
are thick rubber pads between the radiator and 4 memory chips. Another set of
pads is situated between the retention plate and 4 memory chips on the other
side of the card. Hence, the retention plate also serves as another radiator to
some extent. If to take into consideration that memory chips don't consume much
power, this approach is a good idea in general. There are 45 ribs soldered onto
the radiator's main plate which is 2 mm thick. The assumption made above is
correct absolutely: both the main plate and the ribs are copper. Each rib is
70 mm long, 10 mm tall and ˜0.3 mm thick. No doubt that
monolithical radiators are better than those ones soldered from parts, but
advanced copper casting is a difficult process and it would make the device
expensive unreasonably. The 70 mm fan with 15 wings and blue light (T&T
7070TH12C 0.44A 12V) supports pulse width modulated (PWM) power supply for
dynamic speed control, that's why it comes with a 4-pin connector. At the same
time, the whole cooling system is compact considerably because it doesn't occupy
space of the neighborous PCI slot. Air is blown along the radiator's ribs in the
right direction, i. e. inside a computer case.
The other side of the radiator is flat enough, though it could be polished
better. The radiator itself is mounted using four screws.
Overall, the cooling system produces a good impression. There are no heat
pipes or something like that, but it's just well done. At least, it seems to be
of a better effect than a respective reference system by NVIDIA which has been
present on early revisions of BFG GeForce 7800GS OC.
As it has been mentioned before, the heart of this video card is a NVIDIA
G70 graphprocessor of A2 revision operating at 398.3MHz. It consists of a whole
lot of 302 mln. transistors and is manufactured using a 110nm technology
process. Just to get the idea how many it is consider one of dual-core
processors from AMD — Athlon 64 X2 (Toledo). It features 1Mb of
S-cache per core and is manufactured under a more advanced 90nm process, but
comprises only 233 mln. transistors. Back to G70, it's a known fact that
recommended by NVIDIA clock frequency varies between 375MHz for 7800GS cards and
430MHz for 7800GTX boards with 400MHz for 7800GT ones in the middle. However,
this G70 is clocked higher by default (˜400MHz), and it allows BFG to add
a couple of letters to the card's name — "OC" stands for "OverClocked".
That's good, but even the higher speed of the graphprocessor doesn't make it
equal to 7800GT because of architectural differences. NVIDIA has designed G70
with 8 vertex pipelines and 6 sets of 4 pixel pipelines each. Every pipeline can
process shader instructions of the 3rd generation (SM 3.0), though support
for all previous generations is also available. In addition, pixel pipelines are
able to process texture data, but not to rasterise. Unlike NV40 and its
derivatives used for video cards of GeForce 6800 series, where every of 16 pixel
pipelines has been able to rasterise texture data processed, G70 features 16
independent raster operators (ROPs) which communicate with the pixel pipelines
through a high-speed switch called crossbar. Those ROPs also handle all tasks
related to anti-aliasing. So, what is it all about? Big bosses at NVIDIA have
decided that GeForce 7800GTX cards only deserve for fully-featured G70s while
7800GT and 7800GS boards should get used to chips with limited functionality. In
other words, G70s for 7800GT have 1 vertex pipeline and 1 set of pixel pipelines
disabled, and G70s for 7800GS — 2 vertex pipelines and 2 sets of pixel
pipelines disabled. Finally, G70s for 7800GS have lost 8 ROPs what isn't a good
thing at all. It needs to be noted that those pipelines and operators are
disabled in hardware and there is no way to get them working. Software or BIOS
hacks which have been possible with many GeForce 6800 series cards don't stand a
chance for GeForce 7800 series cards. It's obvious why those people at NVIDIA
have agreed upon these castrations: G70 is a big piece of silicon, so throwing
away those cores with at least one defective pipeline would make the rest of
chips which enter the market much more expensive, also a new design should be
developed and manufactured to fill the void of non-born GeForce 7800GS and
7800GT. What to say, not good at all.
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Since G70 has been developed with PCI Express in mind, a PCIe to AGP bridge
chip has to be placed on the PCB. That's an old good HSI (High Speed
Interconnect), known well from many video cards of GeForce 6600 and 6800 series.
It supports AGP 8x with SBA (SideBand Addressing) and FW (Fast Writes).
There are eight 256Mbit Samsung GDDR3 SDRAM 1.4ns (K4J55323QG-BC14 —
PDF datasheet, 1069Kb) memory chips, and each one
contains 4 banks x 2097152 32-bit words. So, they produce a 256Mb array of video
memory featuring a 256-bit data bus. That's very good because these days such a
wide data bus is a must have for high-end video cards as opposed to 128-bit data
bus for mainstream solutions. Of course, GeForce 7800GT and 7800GTX utilise a
256-bit data bus as well. About the clock speed, NVIDIA recommends 300MHz
(1200MHz effective) for 7800GS and 7800GTX boards but 250MHz (1000MHz effective)
for 7800GT ones. Our card is factory overclocked, so its memory speed is set at
313.9MHz (1255.5MHz effective). Nevertheless, let's keep in mind that the memory
chips are labelled as 1.4ns, what equals roughly to 350MHz (1400MHz effective),
and the fastest model mentioned in the datasheet is 1.2ns. So, there is plenty
of room for overclocking, but let's leave it until later.