The old 40pin non-DMA cable is 30 to 35 gauge while Ultra DMA (80-Conductor) is a lot thinner and Cat5e is 24 gauge. The cable itself has a signal loss after 18" while Cat5e can handle about 295 feet.

The big reason why is a IDE cable has no insulation or protection from electromagnetic interference and limits the length of the cable to about 2ft while Cat5e has insulation/protection from electromagnetic interference and the overall length can be much much longer. That's why they came out with the 80pin IDE to try and diminish the data loss, mostly because IDE was originally used for drives that transferred 5MBs to 6MBs a second. Now there's S-ATA that can support faster drives and what not.

A lot of people over at mp3car.com have been playing with this method and seems to work out quite well. Not to mention its easier to tuck/hide the cable.

The finished product depending on how the user made it can be almost as thick as a round IDE cable or really really thick. If I was to make one I would tear off the outer sleeve on the Cat5e and wrap the wires together then ether use wireloom, electrical tape or even heatshrink to seal up the cable.
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