It really depends if the motherboard on the system supports the transfer rate of the hard drive. For example, if the motherboard on the system only supports ATA 66 and the hard drive is ATA 133 the drive will downgrade the transfer rate limiting the transfer rate to ATA 66. Adding an Ultra ATA 133 PCI Adapter card will increase the performance of the drive because the drive in not limited to ATA 66 and can now operate at a ATA 133 rate. However, if you have a drive that is ATA 33 and put it on an ATA 133 PCI Adapter card, it will not increase disk performance because the drive is only capable of ATA 33.