A DOS error message. The full message is|
Not ready reading drive x
Abort, Retry, Fail?
This means the drive door is left open, or the floppy disk is not in the drive. Either put the appropriate floppy disk in the drive or close the drive door (turn lever) and press R.
To switch to another drive, press F, and type in the drive letter you want to go back to when you get the "Current drive is no longer valid>" message. In DOS versions prior to 4.0, type I for Ignore rather than F for Fail.