Think I'll try to install this on my Harlequin at some point. Definitely worth trying in an emulator if you don't feel confident tackling it in hardware. https://twitter.com/TheRegister/status/1245694271912652800

Okay, so I was expecting something a little different. That looks pretty familiar to me. Wonder what the differences are? #ZXSpectrum #PrototypeRom

If you're interested in trying out the prototype Spectrum ROM image for yourself, it's available for download on the Centre for Computing History website here: http://www.computinghistory.org.uk/det/51620/Sinclair-ZX-Spectrum-Prototype/

Note, the 128K style menu on the screenshot has been overlaid by my emulator, and is not part of the prototype 16K/48K Spectrum ROM. Before any folk keel over with excitement.

Ah, there are some differences in the Sinclair prototype ROM. The prototype ROM on the right has extra data near the end of the ROM... The mystery thickens.

At some point I may start doing some digital archaeology on this. I've got just the book to help me out...

Okay, if you try to run any BASIC program in the emulator, you get this error message, at least when running as a 48K. And the ROM doesn't seem to like booting at all in 16K mode.

Looks like system variable P_RAMT is being set low. In ZEsarUX it'ss around 15,000. On ZXSpin it's 60. Should be in the region of 65000. Last byte of RAM available to BASIC. Strange.