On Tue, 14 Aug 2007, Rogier Wolff wrote: > On Tue, Aug 14, 2007 at 10:23:27AM -0400, Alan Stern wrote: > > > The other external disk (also claimed to be full speed) seems to achieve > > > transfer speeds of 20-30 KB which seems OK. > > > > If 400 KB/s is bad, how come 20-30 KB/s is OK? > > He probably means 20-30 M byte/sec.
How could a full-speed device possibly transfer data at 20-30 MB/s? > Some motherboards, when USB 2.0 was still kind of new, have a few > USB 2.0 (high speed, 480 Mbps) ports, and some usb 1.1 (full speeed, > 12Mbps) > > To prevent confusion among consumers, the USB comittee decided that > these USB 1.1 ports should also be called USB 2.0 ports, as they > conform to the slower speed part of the USB 2.0 spec. I prefer to > call them USB 1.1 ports. The whole naming issue is very confusing for people, especially when you realize that USB 2.0 devices don't necessarily support high speed. When referring to devices, it's safest just to call them "full speed" or "high speed" -- or even "low speed", which is perfectly legal for a USB 2.0 device. To make things worse, a high-speed device attached to a full-speed hub will of course be forced to run at full speed. When it comes to ports, the situation is even more confusing. By definition, any port (on a computer's root hub or on an external hub) that conforms to the USB 2.0 spec must be able to run at high speed. So if "the USB comittee", whoever they are, decided to call a port that doesn't suppport high speed a USB 2.0 port, they did so in violation of the spec. The confusion gets even deeper when you realize that the ability to run at any particular speed isn't a property of the port at all -- it's a property of the USB controller the port is wired to, and some ports are wired to two controllers! For the most part this doesn't matter, but it does become noticeable when the BIOS has disabled one of the controllers. > The fact that not "EHCI" but "UHCI" is driving one of your ports > is a strong hint that it is a "max 12Mbps port". Or that ehci-hcd simply wasn't loaded. Maybe you didn't notice, but none of the buses in Wim's usbview listing supported high speed. Alan Stern ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Linux-usb-users@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-users
