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AST RESEARCH, INC.        TECHNICAL BULLETIN # 1106                3-27-95

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				FLOPPY DISKETTE FORMAT COMPATIBILITY


PROBLEM

Attempts to format a 1.44MB as a 720KB, or a 720KB as a 1.44MB may produce an 
unstable product up to and including loss of data.

CAUSE

Some drives rely on an internal sensor to determine the diskette type, and 
therefore the permitted data density, and others rely on the state of a 
control line from the system floppy controller.  The Epson and Mitsumi drives 
are set to react to the sensor in the drive.  If the sensor detects the extra 
hole in the diskette jacket of a High Density diskette, it reads and writes 
only 1.44 MB format diskettes.  If it detects the absence of the hole in a 
Double Density diskette, it reads and writes only 720 KB format.  An Alps 
drive, on the other hand, does not include the internal sensor, and relies on 
the signal on pin 2 of the interface to determine the read and write density.  
On the Alps drive, you can therefore record 720 KB on a High Density diskette 
or 1.44 MB on a Double Density diskette.

SYSTEMS AFFECTED
AST PART NUMBER AND DESCRIPTION

AST factory installed 3.5" floppy drives.

SOLUTION

A 1.44MB floppy disk should only be formatted as 1.44MB, and a 720KB diskette 
should only be formatted as a 720KB diskette.