According to Wikipedia, USB 2.0 can support up to a maximum of 5 load units at 100 milliamps per load unit. So the port is required to supply up to 0.5 A at 5 VDC (2.5 Watts).
I just looked up several 2.5" 320 GB 5400 RPM drives from Hitachi (5K32) and Seagate. I also looked up a 2.5" 7200 RPM 320 GB Hitachi drive (7K320). The startup power for all is at least 5 Watts. Once running, the power for seek is 2.2 Watts or lower. So, if the USB port on the Thinkpad is power limited at the USB 2.0 spec, the 320 GB drives I looked up will probably fail to start with a single USB port supplying power. I expect that is why my Lacie 7200 RPM drive fails to start when powered from a single USB port. I expect that is why Lacie provided a wall wart with my 7200 RPM drive and they didn't with the very low power 1.8" 60 GB drive (2.5 Watt max at start). For reliable external drive performance, I'd expect you would need to use 2 USB ports or some sort of external power. A 6-pin firewire 400 or 9-pin firewire 800 port should also power a drive if the enclosure and computer had such ports. The firewire 400 version might perform a bit better than the same device using USB. If the drive has a high data rate, firewire 800 would provide better performance than either USB or firewire 400. Note that there is a USB 3.0 spec and it allows higher power (6 load units of up 150 mA or 0.9 Amps). Still not rated high enough for startup loads of 1.0 or 1.1 amps listed for the hitachi 5400 and 7200 RPM drives. Stuart > > Another exception here, I have the Seagate Momentus 5400 160 gb drive in an > enclosure and I need either the second USB port OR the wall wart to have it > run. Otherwise it just clicks. > > Stuart Friedman > > > OK, thanks for the correction. > > Maybe I should have said "any external 2.5" 5400 RPM drive". > > > Stuart Biggar wrote: > >> There's nothing about either the T43 or this LaCie drive that would > >> cause any incompatibility between them. Only one USB cable is needed, > >> because a singe USB port on any T4 series Thinkpad provides sufficient > >> power for any external 2.5" drive. > > > > > > That is not my experience. I have a Lacie enclosure with a 7200 RPM > > Hitachi 2.5" laptop drive. The drive will NOT spin up correctly when > > plugged into a USB port on my T43p. It works fine when powered > > by a provided Lacie power wall wart (quite small) and then plugged > > into either of the two USB ports on my T43p. It does work OK > > when powered through a 6-pin Firewire connection with an iMac but > > does not work correctly with only the USB connections on an iMac. > > The Lacie enclosure supports 400 MB firewire (standard 6-pin > > socket) and USB. > -- > Stuart Friedman > Montpelier, VT USA > 802.522.6228 > _______________________________________________ > Thinkpad mailing list > [email protected] > http://stderr.org/cgi-bin/mailman/listinfo/thinkpad _______________________________________________ Thinkpad mailing list [email protected] http://stderr.org/cgi-bin/mailman/listinfo/thinkpad
