This interface is based on the CH376 chip and allows access to USB mass storage and other USB devices on CPC.
The CH376 chip implements FAT32 in hardware, which means no filesystem driver is needed on the CPC side. It also implements the lower level aspects of USB, making it relatively easy to write drivers for other USB devices (mouse, joystick, ...).
Albireo also includes a high-speed serial port, allowing speeds past the megabit per second mark. [http://pulko.mandy.pagesperso-orange.fr/shinra/cpc-usbalbireo.shtml CH376 Albireo interface homepage]