I implemented it to see what Windows 1.0 looked like in 4 colours:
But I thought I might as well make it up into a proper and reasonably complete patch.
- If your system's BIOS supports video ROM shadowing, disable it before switching to the Sigma card - the card does not work with its ROM shadowed.
- The card uses non-maskable interrupts to implement hardware-level compatibility with CGA. If you find this leads to instability (for example, the PC hangs when trying to scroll the screen) this can be disabled in the card configuration - this will leave it compatible at the BIOS level only.