Answer: The hard drive will function at ATA/66 speed.
Explanation:ATA( advanced technology attachment) is a type of Disk drive that integrates it features of the drive controller into the drive it self directly,ATA range from ATA/1,ATA/2,ATA/3,ATA/33,ATA/66,ATA/100. When ATA/66 is installed on a computer with ATA/100 capable,the hard drive of the Computer will function at the speed of ATA/66.
It is recommended that when working with an ATA/100 capable drive it is better to install an ATA/100 disk drive.