On Thu, Nov 27, 2008 at 5:20 PM, Alan B. Pearce wrote: >>The 30MB/s I get could very well be the physical >>limit of the drive, or it could be USB, > > Interestingly, reading 'USB Complete' by Jan Axelson, she gives this as > around the maximum attained speed at 480MBit/s. Yeah that is about right. It is the same under Linux as well. http://www.linux-usb.org/usb2.html "Where "quick" often means up to 30 MByte/second, with off-the-shelf hardware". http://www.everythingusb.com/usb2/faq.htm "As far as we know, effective rate reaches at 40MBps or 320Mbps for bulk transfer on a USB 2.0 hard drive with no one else is sharing the bus. Flash Drives seem to be catching up too with the some hitting 30MB/s milestone." "A fast usb host can achieve 40 MBytes/sec. The theoretical 60 MB/sec cannot be achieved, because of the margin taken between the sof's (125 us), so if a packet cannot take place before the sof, the packet will be rescheduled after the next sof. On top of that, all the USB transactions are handled by software on the PC. For instance, a USB host on a PCI bus will send or receive the data via the PCI bus; the stack will prepare the next data in memory and receive interrupt from the host." And USB 3 Superspeed is said to be several times faster with initial pre-release silicon. http://frescologic.com/index.php?option=com_content&view=article&id=56:fresco-mass-storage-devcon&catid=34:news&Itemid=50 Xiaofan -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist