The core of the OS needs 64 KB ROM. Compatible products are EPROM-cards, the ROM-RAM-BOX, [[SYMBiFACE II]], RAMcard or similar products. If you don't own such a card, you can take a look at FutureOS by using a compatible CPC Emulator (WinCPC, Caprice, WinApe).
The core of the OS itself is executed directly in (Pseudo-)ROM or EPROM where it is divided in four 16 KB blocks. It jumps between the ROMs with the help of a little common area. The free RAM can be used for applications and DIRectory buffering. Furthermore it contains memory management and , file-handlingand Low/Mid/High-level routines to access the hardware. From AmsDOS/Basic you can start FutureOS with the RSX commands |OS or |FDESK. If you use |FDESK you can leave FutureOS and get back to BASIC where you have stopped before - the first 48 KB (not the screen) have been preserved.
FutureOS only runs well on a CPC6128 or 6128plus, because they support the RAM configuration &C3 (which is essential for the mouse arrow of the GUI).