It’s fair to say that
neither ATI or Nvidia got their dual card solutions
spot on first time around. While they had great
performance and a high level of stability there
were various niggles like limited resolutions or
card compatibility restrictions which affected the
two approaches to dual card rendering. With a recent
driver update Nvidia went a long way to solving
many of the limitations affecting SLI systems and
on the hardware side of things also released a chipset
capable of two 16xPCIe graphics slots. This meant
that in specific areas ATI were really lacking in
features when compared to the competition, especially
with only the X8 series Crossfire available to buy.
Now with the launch of Crossfire
for the X1800 series ATI effectively have a second
generation of Crossfire coming to market which allows
them to even the playing field again. So will
things be more successful for ATI this time round?
X1800XT Master Card
As with the X850 version
of crossfire the X1800 series require the use of
a master card. This card features the components
required to compose the image displayed on screen
when in single or dual card mode.
At first glance the card
appears to be a pretty standard affair. It has a
dual slot cooler as well as the passive heatsink
at the rear of the card. Underneath the cooler we
have a R520 core clocked at 625mhz coupled with
512mb of GDDR3 running at 1440mhz (which is slightly
slower than a standard XT)
What is different is that
the master card features ATI’s new "twenty"
PCB (you can tell the difference as the initial
cards were XX-XXX-10 and the new ones are xx-xxx-20)
and therefore has six power coils for power filtering.
Many of the initial cards released feature a give
power coil design however these work perfectly with
the 6 coil master cards.
(NOTE: The majority of
X1800XTPE cards have six coils also).
The rear of the card is a
pretty standard affair as you can see from the picture
Turning the card back over
and looking even more closely allows us to see one
major change to the design of the card. Just underneath
the fan housing at the top and bottom of the card
you can see two additional chips. The bottom chip
is a Silicon Image 163B dual-link TMDS receiver
chip which is partly responsible for allowing
the X1800 Crossfire to process resolutions above
1600x1200 (There are actually two of these chips
on the card).
Resolution being limited
to 1600x1200 was the one major limitation of the
X850 series crossfire due to its single link design.
The new maximum resolution available by combining
the 2 SI receivers (running at 165mhz and capable
of receiving 2 x 1600x1200 @ 60hz) with the new
more powerful composing engine is 2560x1600.
The SI Chip which you can
see at the top of the card is a TDMS transmitter
which is used to output the signal to any displays
connected to the master card, again there are two
such chips on the master.
The second major part of
the Crossfire hardware sits directly beside the
SI chips and is the Xilinx Spartan XC3S400 FPGA,
a logic chip which handles the image composing (including
blending for Super AA mode). Interestingly this
chip is programmable and can be flashed
should ATI decide to add features to the design
in the future.
Turning to the side of the
card we can see the cards bracket, this allows you
to identify it as a master card immediately, whilst
you have a DVI port as normal you also have the
new style crossfire connector for the higher spec
Crossfire cable. There is no s-video out however
on the master card.
The new design Crossfire
cable, as with the older X850 design, takes the
output of the slave card and transfers it to the
master card and is also capable of outputting to
a display. Pictured below are the three connectors
attached to the cable.
Currently ATI are using the
existing crossfire chipset for their full range
of products. The chipset codenamed RD480 is the
basis for many retail motherboards such as the DFI
LANParty UT RDX200 CF-DR, Asus A8R-MVP
and Sapphire PURE
Crossfire and all work in the same
way. Just plug in your master to the lowest numbered
slot and your slave to the 2nd slot and you are
ready for action (This results in you using two
8x pcie slot mode rather than two 16x slots as with
some SLI systems).
The new master card is also
compatible with the X1800XL Radeon, when connected
to one such card the Crossfire master card will
deactivate 256mb of its memory (reboot required)
and run quite happily in dual card mode.