@avalos @jalefkowit The triple fault technique and the keyboard microcontroller reboot methods were both used to reset the CPU without rebooting the rest of the PC.

The problem with these techniques is the very poor performance that comes with it. The CPU state needs to be preserved prior to using this, since many of the CPU registers are destroyed in the reset process (e.g., CS is forced to 0FFFFH), the code needs to check done state variables to make sure it's not a cold boot, etc.

Then there's the issue of having to manually swap out the lowest 640KB of memory as needed to bring in the DOS application, and you prayed that the DOS application didn't go into protected mode on its own, thus granting it ring-0 access to the rest of the system memory.

Even if the 286 supported clean re-entry to real mode, you'd still have major issues supporting multitasking in 286 mode.