Torch BBC Model B
Torch BBC Model B
Here's the ATPL Sidewise Sideways RAM/ROM expansion board. As well as some logic circuitry, there are spaces for the OS ROM and 7002 ADC displaced from the motherboard. There's a battery circuit, which isn't fitted, and I'm not sure that the two-way switch on the left-hand side near the cut-in is original, and somebody has been having a go around R1 adding an extra diode.
Beyond that, there are 13 sockets for ROMs, the idea being that 2 8K RAM chips would be used to make up a single bank of 16K sideways RAM, which was common in the 1980s as presumably 62128 chips were harder to come by. BASIC is on this expansion board, whether that is required or advised, or just user preference, I'm not sure.