This is what happens when the Master 512 is first turned on with the Tube switched off. Note that the "ACORN" of ACORN MOS is in capital letters, indicating that the computer is fitted with MOS 3.50. This edition of the Master operating system was available only as a user upgrade. It was never fitted as standard by Acorn as, according to the user guide, it was incompatible with quite a lot of software which used unofficial OS calls.

For some reason - I think either because of MOS 3.50 or the ROM boards - the start-up sound effect is a bit different than usual. There is a very brief low-tone beep followed by a pause of about a second and then the VDU 7 bleep.