Raw disks on computers on which other operating systems, such as Microsoft Windows systems, are installed. This can be accomplished by booting(i.e., starting the computer) from a liveCDversion of Linux such as Knoppix instead of from the operating system installed on the HDD. A liveCD is a CDROM that contains an operating system that is configured so that a computer can boot directly from it instead of from the installed system.
Attempting to edit raw disks is very risky and should be avoided if at all possible. This is because even a single byte out of place can cause a computer to malfunction, and it could result in the need to reinstall the operating system and the possible loss of data.