The old IDE(ATA) came in several standers. ATA/33 (33 MBps), ATA/66 (66 MBps), ATA/100 (100 MBps) and ATA/133 (133 MBps).
Even though the ATA/133 transfered at a speed of 133 MBps, the Hard Disks never used that full speed. That's because the Heads in the Hard Drive cannot read data from the...