The AMSSIO interface is a RS232 interface by the dane, Martin Zacho. As opposed to other serial interfaces the AMSSIO is meant to be installed on top of the Z80 CPU in the CPC. However the circuit can easily be built on a breadboard and connected to the expansion port as well.
AMSSIO exists in 3 different versions.
A new and improved version is the AMSSIO II.
The software for AMSSIO can simulate a disk drive and a printer on a PC connected via RS-232. The software comes in two parts. The first part is for the CPC. It replaces relevant parts of the jump block, redirecting disc and printer access via RS-232. The second part is called CPCSHELL and runs on a PC under DOS or Linux. Part of the PC harddisk can be used as a giant CPC disk via this mechanism.
A spare PC can therefore be used as a method to add a cheap harddisk to the CPC. Although the software required on the CPC reduces compatibility somewhat it works for most well behaved applications and games that consist of a single binary (no special loader).
Other RS232 interfaces for the CPC
AMSSIO project lives here! (broken link)