I wasn't talking about LiveCDs or VMs either. Back in 1999 my PC had one FAT32 partition (Win95), onto which I installed QNX, BeOS and Mandrake. These 3 operating systems each created a file of around 500MB, which was a HD image. The bootloader/kernel and/or some other essential parts were launched from inside Win95, which was then shut down and the alternative OS booted. Your Google skills must be poor, I found this info about BeOS on the second page of results. For details about QNX, the first page of results throws up the necessary info. Well, that's proved me right, I won't bother finding something that proves Mandrake used the same technology.