This is a closer view of the main PCB from the back of the machine up to the backplane. There is a partly-handwritten serial number in the bottom left-hand corner and the issue number and description ("4M/G Main PCB") in the top right. Also in this picture we can see the four RISC-OS 3 ROMs and a spare bank for a 5th ROM, and the connectors for an Econet module.