Additional peripheral cartridges by companies such as PRES (via their ARA/ARA2/ASR products) allowed sideways ROM capability, that allowed the standard Acorn ROM space to be programmatically mapped out for alternative EPROMs, either physically via ZIF Sockets, or 'virtually' via ROM images loaded into (battery-backed) RAM in the same ROM address space. This enabled the Electron to achieve the same functionality as that provided by the expansion ROM slots under the keyboard and on the bottom-left of the BBC Micro B keyboard.