RISC OS has the concept of "OS units" which don't map directly onto pixels 1:1, and it was possible to fiddle with the ratio on the RiscPC from 1994 onwards, giving reasonably-scaled windows and icons in high-resolution modes such as 1080p.

It's hinted at in this tutorial, but you'd have to go through the Programmer's Reference Manual for the full details: https://www.stevefryatt.org.uk/risc-os/wimp-prog/window-theo...

RISC OS 3.5 (1994) was still 2MB in size, supplied on ROM.