VIA Chipsets slow down PCI cards

ATA/133: PCI-Timing

By use of a PCI probe with our logic analyzer we also checked what was happening within the PCI bus during theses transfers. With an Intel 845 based system we found a constant flow of data, whereas with VIA boards these transfers are interrupted all the time.

To take these scores, we made Maxtors DiamondMax D740X work with the Promise Ultra133 TX2 in burst mode.

After these 24 packets are transferred, a new address gets requested. The PCI bus can only transfer blocks of 96 bytes of data within one burst with this solution.

With Intels chipsets being able to transfer 1024 packets within one burst, this makes a whole transfer of 4096 bytes. As a consequence, Intels chipsets gain a higher transfer rate overall on their PCI bus than VIAs chipset.