VINCULUM's VNC1L-1A is the ASIC(Application specific IC) IC for USB Host.Check the datasheet and i am sure u will understand.
In brief one can connect any microcontroller to VNC1L-1A via SPI,UART,Parallel FIFO interface.i am using a UART interface for the same and i have found it very easy.It's just like AT commands used for GSM modems.Using theirs simple command set one can acess all pen drives,usb hard drives,etc.(All BOMs which support FAT12,FAT16,FAT32 systems)