BACKGROUND: The Apple 800K drive for the Macintosh requires
the following software to run on a 128K or 512K Macintosh:
/HD20 Driver File
/System File Revision 3.0 or greater
/Finder File Revision 5.0 or greater.
A Macintosh Plus does not require the above listed software.
PROBLEM DESCRIPTION: Connect 800K external drive to
Macintosh 512K (NOT upgraded to a Macintosh Plus). Boot
up using Finder 5.0 or greater and System 3.0 or greater.
Attempt to read an 800K disk from the external drive: Mac
bombs with error ID=4. Attempt to initialize a 400K disk in
the 800K external drive: Macintosh displays "Initialization Failed"
dialog box. Attempt to boot an 800K disk on the external
drive: Macintosh bombs with "sad Mac" error 0F0004.
CAUSE: The system file "Hard Disk 20" (the Hard Disk
20 driver) and the other files listed in "BACKGROUND"
(above) are needed for the "old ROM" Macintosh to
communicate with volumes (drives) larger than 400K.
The necessary files may not be on the startup disk.
CURE: Install the files listed in "BACKGROUND" on your
startup disk. If you don't have the files available, contact
your local support center for copies. They are free of charge.
If the above cure doesn't fix the problem, refer to the
Tech Procedures to obtain the general troubleshooting
for this product.