Cool, I’ve wanted an OS ROM chip since the early nineties, and often wondered why nobody seemed to be doing it. Guess they were all along!

You technically didn’t have to park the old MFM and RLL drives, but if you didn’t, then you just had the drive heads resting on the platters after you shut them down. Then if you bumped or moved the PC at that time, it could scratch the disk like a record. If you never tried to move it, there probably wasn’t much risk.

From the sound of it, the HDD in your Tandy probably would have been an MFM or RLL drive, and depending on the drive model, it either autoparked the drive heads or didn’t. As a PC clone running MS-DOS, the command was probably supported, but maybe not needed. Or you may have just been the equivalent of one of those rebels who held down the power button every time they wanted to shut down the PC and always got away with it!