The extra instructions were mostly fine, the NEC V20/V30 implemented them too, the 186 had built-in peripheral functions like timers and the interrupt controller that were different to those in a PC.

You couldn't use the array bound check instruction as it used the interrupt used by the PC BIOS for Print Screen.

That is a hilarious limitation. I can just see someone building a test program to try it out and wondering why his printer is suddenly spitting out screenshots.

I was going to say "that's now how it works", but actually, thinking about it... I think that's exactly what would happen, heh?