What is the reserved data at $FF18 - $FFFF?

[JMcGibbitts]

Hi.

I see data from address $FF18 (65304) - $FFFF. 231 bytes. It seems to start with F3 0D CE 0B E3 50 CE 0B... I have not seen it change size or start address across a few programs.

What is this data? Does it remain constant / static?

Provided I keep my main program code < $C000 and I copy this reserved data from $FF18, into all 128K banks 1-7, will I be free to use 128K paging as I choose, loading data and / or binary code into each page at specific addresses?

Will the program need this reserved data in the other 128K pages or is it maybe only used during program initialisation?

Thanks!

[boriel]

That's mostly old RAMTOP data plus UDG old data (unused). So it's not reserved. If you use --sinclair for compatibility, then yes, UDG will be used in another memory region.