Everything you Need to Know About ATA-66, ATA-100 and ATA-133 Hard Disks


Theorically ATA-33 hard disks have a 33 MB/s transfer rate, ATA-66 hard disks have a 66 MB/s transfer rate and so on. But achieving maximum performance with hard disks from ATA-33 on is not a matter of just plugging in the new hard disk on your computer. A lot of times, you won’t achieve not even close to the hard disk’s maximum transfer rate. In this tutorial we will explain why this happens and how to correctly set up your computer to reach the maximum transfer rate you hard disk is able to provide.

You can check the current transfer rate from your hard disk by using the software HD Tach. Our Figure 1 was taken in a computer with an ATA-66 hard disk. As you can see, the transfer rate achieved was only 8.2 MB/s, and the CPU utilization was over 90%.

Bus Mastering DisabledFigure 1: 8.2 MB/s transfer rate and 92.7% CPU utilization with an ATA-66 hard disk. Something got to be wrong!

This tutorial is about why this problem happens and how to fix it. After reading this tutorial and applying the suggested corrections to your computer, you should achieve something like shown in Figure 2, where the same hard disk, on the same computer, achieved 46 MB/s and 2.7% CPU utilization.

Bus Mastering EnabledFigure 2: After correct computer configuration, 46 MB/s transfer rate and 2.7% CPU utilization.

You have to keep in mind that the listed transfer rate (66 MB/s, 100 MB/s, 133 MB/s etc) is rarelly achieved, as you can see in Figure 2 where an ATA-66 hard disk achieved 46 MB/s. But far better than 8 MB/s!

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Author: Gabriel Torres

Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.

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