An IDE drive is only low level formatted at the factory
Yes indeed. Low level format overwrites not only the data and partitioning
information, but also the markings that constitute the tracks and sectors.
You used to be able to actually change the numbers of tracks and sectors
on the drive, and their physical location.

When today's HD manufacturers supply a "low level format" utility,
all it does is erase all data from all sectors of the drive, including
the MBR, putting the drive in the same condition as new.

Naturally your OS will not be there any more. You will have to partition,
format, and install an operating system.