I have a "favorite old computer" that can dual-boot real-mode and XP, use for embedded system development. It would run DOS reliably, but XP would crash after running 10 minutes or so. Thought it was bad memory- was not. DOS would allow both-fans to kick in, XP- one fan and crash. DOS running at 2GHz is fast. Read online that someone else had the same problem. They were advised that this was an issue with the Paste used to hold the CPU Heat Sink on. Yup. That was the problem. The paste had flowed off the CPU die and onto the rest of the chip. Put it back onto the die, reseated the heat sink- it's running.