On Tue, Mar 29, 2011 at 4:07 AM, Ken Schaefer <k...@adopenstatic.com> wrote: >> Note also that spec USB can't provide enough power for many (most?) 2.5" >> drives. >> The double-plug USB cables are a hack that happens to work sometimes -- maybe >> even most of the time -- but sometimes it doesn't. > > I've got more than 20 different USB 2.5" enclosures sitting at this desk > alone (some > are no-name, others branded: WD, Seagate, Lacie), and they've worked on every > laptop I've ever owned except the Dell D600. That includes a Seagate 12.5mm > 1TB > model. I think that problem was solved years ago.
The USB spec says devices are allowed 100 mA to start, and can negotiate up to 500 mA. Most double plug hacks doesn't put any intelligence on the second plug, so it can't negotiate anything. This violates the spec. It's not a problem that can that can be "solved" within terms of the spec.[1] I've encounter a few systems over the years that didn't like a given enclosure. It's fairly random -- which makes sense, since we're treading in the margins of error outside the spec. I know you've got enough experience with IT that I shouldn't have to explain the difference between "usually works, despite spec violations" and "spec says it should work"[2]. :-) -- Ben [1] I imagine an enclosure could put some minimal intelligence on the second plug, so that it could negotiate a full 1 A combined. Some enclosures may even do this. But the cheaper ones I've encountered don't. [2] And of course "spec says it should work" doesn't always mean "usually works". ~ Finally, powerful endpoint security that ISN'T a resource hog! ~ ~ <http://www.sunbeltsoftware.com/Business/VIPRE-Enterprise/> ~ --- To manage subscriptions click here: http://lyris.sunbelt-software.com/read/my_forums/ or send an email to listmana...@lyris.sunbeltsoftware.com with the body: unsubscribe ntsysadmin
