The PCI bus is even slower then the current FSB's of todays boards. Most people don't realize that the circuitry of the mainboards are segregated. The CPU, Memory, GPU constitute the FSB (frontside bus). It is normally set on current boards to the clock of the processor. The IDE bus is separate from the PCI bus. The IDE bus is a 64bit bus while the PCI bus is 32 bit. The ATA 100 7200 rpm drives on the IDE bus are 66Mhz @ 64 bit X 1.5 clock. The new buses on the boards are now 128 bit. You can certainly get a PCI ATA 100 adapter card, but your bios must accept booting from it. Most older bios will not accept a PCI card connected drive as its main boot drive. The card must have a bios rom that overrides the system bios in this regard. It doesn't always work with older systems. I depends upon the chipset and bio version used. If it works you will have a ATA 100 drive connected via 80 wire cable to a SCSI card sitting on a 32 bit bus running at 33Mhz x 3. The drive was designed to run on a 64 bit 66Mhz bus not a 32 bit 33Mhz bus. So of course it will be slower because it will default to 5400 rpm due to the 33Mhz 32 bit PCI bus. People incorrectly assume because the drive works, it means they are getting the actual performance they think they are. Most of the time they aren't. Frankly simply attaching the ATA100 harddrive to the normal IDE port with a standard IDE cable and simply running it as a UDMA 66 performance level drive is more stable and faster then using a cheap adapter card.