January 10, 2008

IDE cable termination

I never gave much thought as to how IDE cables are terminated. Recently, I broke an exceptionally small IDE cable that lives in my hard drive enclosure — I can never figure out how to pull IDEs out by the head, and so I always end up yanking on the cable, often detrimentally. :)

In breaking the head of the cable, I found out that this IDE (and I assume this holds for all IDEs) is "vampire tapped", reminding me of 10BASE5 Ethernet technology. Effectively, all 40 of the insulated wire sheaths are pierced by sharp spikes in the terminator. I'm not sure if this vampire tap method also holds for the three-head IDEs (board/master/slave) — I'll have to dismantle one of those in the future. It might be fun to look into IDE arbitration protocol at some point to figure out how those three-head IDE cables work properly. Are they a single bus with three vampire taps, or two separate buses with the middle device acting as an arbiter?

At any rate, it's real hard to get one of these terminators situated right after you knock it out of place. There are holes from the previous termination that you have to place just right. So far as my external enclosure is concerned, it looks like I've gotta find a new cable. :/