The Multiface is an interface made by Romantic Robots. With this interface you can save a programm without stopping it. After loading in the made copy, the programm continues from where you saved it.
This Multiface is designed for the Spectrum 128. It works on the Spectrum 128 and +2, but also on all 48k Spectrums. Not on Spectrum +2A (black) and Spectrum +3.
Only with this Multiface you can save 128k programs by the mentioned method. Of course +2A and +3 users can do the same with the Multiface +3, which is hard to get.