You need to use an 80-wire flat cable to install ATA-66 hard disks and above. The 80-wire flat cable uses the same 40-pin connector as the standard 40-wire IDE cable, but it has an extra ground wire between each regular wire to cancel noise. If you are unable to identify which kind of flat cable your computer is currently using, just count the number of wires available! Is just that simple.
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Figure 8: 40-wire flat cable vs. 80-wire flat cable.
On Figures 9 and 10 you can see exactly what happens if you use a 40-wire flat cable instead of an 80-wire cable. On Figure 9 the data has a lot of noise, which was suppressed with the use of the 80-wire flat cable, as shown on Figure 10.
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Figure 9: ATA-66 data transmission using a 40-wire flat cable.
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Figure 10: Same data transmitted using an 80-wire flat cable.
If you have a ATA-66 hard disk or above you have to use an 80-wire flat cable, or your hard disk will achieve only a maximum 33 MB/s transfer rate.
After correcting the problems you may have on your computer, you can check the hard disk transfer rate with the HD Tach program. The CPU utilization must be below 10% and the transfer rate should be higher than before. Please notice that it is almost impossible to achieve your hard disk maximum transfer rate (100 MB/s for an ATA-100 hard drive, for example), because this number is a maximum theoretical transfer rate. Actually, this number is the IDE port maximum transfer rate, not the hard disk maximum transfer rate. It means that the port can handle transmittions up that number, but that doesn't mean that your hard disk will achieve that. For ATA-66 expect something around 40 MB/s and for ATA-100 and ATA-133 hard disks expect something above 60 MB/s. The higher, the better.
You can also play with bus mastering drivers (Microsoft drivers vs. chipset manufacturer drivers) to check which version brings better performance to your hard disk.
