Rounded IDE cables is a recent fad to come about the geek world. This involves taking the old 80's style and slicing down between the wires or ordering ones from someone like Thinkgeek.
There has been quite a controversy about the performance of the rounded cables. Some experts are saying that there is a 60% drop in performance, but with test after test it is showing that there is only an average of 1% drop in performance.
So for you people who wanted to make the inside of your computer look tech, but was afraid that you might take too much of a perforance hit, go right ahead with rounded cables and get out of the 80's.
The test results as performed by Mike Kitchenman (Kudos!):
ATA 33 Flat
Max Min Sustained
Read: 27410 18170 22714 kbs
Write: 27243 12949 19836 kbs
RA: 13.6 ms
Burst: 30.1 Mb/s
ATA 33 Hand Rounded
Max Min Sustained
Read: 27270 18170 22541 kbs
Write: 24632 10929 19568 kbs
RA: 13.6 ms
Burst: 29.9 Mb/s
ATA 100 Flat
Max Min Sustained
Read: 33262 18181 24369 kbs
Write: 26538 12962 19730 kbs
RA: 13.7 ms
Burst: 75.9 Mb/s
ATA 100 Hand Rounded
Max Min Sustained
Read: 33256 18191 24339 kbs
Write: 26215 12957 19870 kbs
RA: 13.7 ms
Burst: 71.7 Mb/s
ATA 100 Machine Rounded
Max Min Sustained
Read: 33287 18178 24372 kbs
Write: 26593 13699 19689 kbs
RA: 13.7 ms
Burst: 76.0 Mb/s
Key:
Read: Read speed on HD
Write: Write speed on HD
RA: Random Access Time
Burst: Read Burst Speed
Source: http://www.systemlogic.net/articles/01/6/flatvsround/page2.php