I've just read in the Intel PXA27x-specification. And there are some interesting things about the USB-capabilities of the processor:
USB-client: USB 1.1 with max. 12 Mbps
USB-host: USB 1.1 with max. 12 Mbps. The host provides 3.3 V to clients but the normally necessary 5 V for HDD or something "bus-powered" are not provided. And, the 3.3 V output is combined with a max. current of 25 mA and therefore 82.5 mW. That's much too less for a harddisk. According to Toshiba, Hitachi, Seagate and Fujitsu, current 1.8 inch harddisks need at least 1.2 W for spin-up.
Intel (see ftp://download.intel.com/design/pca/appli...als/2800002.pdf and ftp://download.intel.com/design/pca/appli.../28000502.pdf):
The +5 V VBUS source from USB host controller, which must be available for bus-powered peripherals, must be supplied from an external source, but it is not part of the PXA27x processor silicon.
I don't think Sharp added some additional USB functions which were not provided by the PXA270.
It's too bad, I really thought I could use an external HDD without power supply.