Since high school I've wondered what those registers in the 0x3c0-0x3cf range are for. I found them in a book somewhere and started writing to them to see what

Since high school I've wondered what those registers in the 0x3c0-0x3cf range are for. I found them in a book somewhere and started writing to them to see what would happen. The only one I found interesting was the PEL mask register, which was useful for practical jokes at school (I wrote a TSR to write to the register periodically, causing the colors to change). This is the first I've heard of someone using one of these registers for something useful. It's a shame I can't send this knowledge back in time to my former self.