The VIA KT400 chipset: ahead of the pack?
The KT400 has been drastically improved from the KT333 chipset to support AGP
8x compatible videocards, "un"official DDR400 compatibility and and undergone an
overhaul called V-link.
V-link is the spiffy name used to
describe the communications link between the northbridge and southbridge, and this directly relates
to yet another 8x nomenclature. KT4000 features an improved rate of AGP Texture transfer, increasing
from 4x (1.06 GB/s) to 8x (2.1 GB/s).
Perhaps with more bandwidth available, videocard
manufacturers will try and take advantage of AGP Texturing more. We were able to
get an ECS AG400 (Xabre400) to run at 8x AGP properly, but the BIOS would not
allow us to change the AGP rate to anything else.
As you can see,
the V-Link that connects the KT400 Northbridge to the VT8235 Southbridge runs at
8x V-Link and has an actual transfer rate of 533 MB/s - doubled from
the old transfer rate of 266MB/s for the old 4x V-Link
found in KT266A, and KT333 chipsets.
With bandwidth
hungry devices such as IEEE 1394 (Firewire), USB 2.0 and IDE RAID it was
possible to saturate the original V-Link data bus (266 MB/s) between the Northbridge
and Southbridge. To solve this potential problem, VIA has doubled the bandwidth between them
to 533 MB/s which should be more then enough to satisfy
even the most well equipped computers.
In
regards to memory, VIA can't adhere to a standard which doesn't
yet exist, and that's the official reason why the VIA KT400 does
support DDR400 (aka PC3200) RAM. Unofficially though, there have been
rumors
floating around the web that VIA may be having problems getting the KT400 chipset to
run properly with DDR400 compatible memory.
We
encountered a few problems getting a stick of 256MB Corsair XMS3200 CAS 2 to run
at 400 MHz in our tests. The system would simply
lock up at POST.
Lowering the CAS Latency to 2.5 allowed the system to run
flawlessly so this may not be the fault of the motherboard. As
there is no likely sight of an official JEDEC DDR400 (aka PC3200)
standard on the horizon, all current DDR400 DIMM's on the market are really only
DDR333 DIMM's which are overclocked and may have compatibility
problems with certain motherboards/chipsets.
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