Non-resigning computers

We all know that there are few, if any, computers out there that will opt to resign rather than play out a hoplessly lost game to the finish. The following is a game between my Excalibur chess station (on its highest level setting) and one of chessmaster 8000's personalities:

So, does anyone know why 21.Rxe1?

And when would you have resigned?

If the rook doesn't take, then 21. ... Nc2 fork.

It's the user-interface, not the engine, that decides when to resign. Fritz, Aquarium, and Arena all let you configure the resignation point.

I couldn't find the option in my Rybka/WinBoard combination (downloaded from here: http://www.chess.com/download/view/portable-winboardx--rybka-22---updated-setup)

It's a real pain when I'm trying to practice some endgame positions (like K+B+B vs K or K+B+N vs K or some King and Pawn endgames) and the engine keeps resigning....

Does anyone know where to turn it off in WinBoard?

Only the weak and the meek resign

I got a resignation out of my Novag Obsidian just the other night (it was set on a level that has roughly the same strength as a novice after a three-martini lunch).  I think it's a nice feature although not essential.  Gives it a bit of a human touch, and if you want to, you can force the computer to play on to the bitter end.

Thanks - didn't spot that

Ofcourse, the rook on a1 doesn't actually do anything throughout the entire game, whilst the other rook would have been a useful defender.