The Viglen Sideways ROM Cartridge system allows a user to change out ROMs for the BBC Micro without the need to open the case every time a ROM needs changing. It came with a modular storage system which can be seen on the lower right of the photo which protects the ROM cartridge edge connector when it isn't fitted to the socket on the BBC Micro.
The socket on the BBC Micro is fitted to the ROM expansion slot commonly referred to as the "ash tray" and has a dust cover that fits to the socket keeping dust and contaminants out of the socket when it is not in use.
Fitting a ROM Cartridge to the socket is easy as it simply plugs into the slot but it must be fitted and removed whilst the BBC Micro is switched off.
The Viglen Cartridge is a relatively simple circuit board encased in a plastic case.
To fit a ROM or EPROM to the cartridge, the two screws holding the two halves of the case need to be removed.
Here's a quick shot of the entire cartridge disassembled. You don't have to do this to fit a ROM or EPROM.
Here's a detailed shot of the cartridge circuit board.
After fitting a ROM or EPROM, the cartridge is ready for reassembly.
provided courtesy of Stardot STH forums