The external 800K drives will work on a Macintosh 512K that does NOT have a
ROM upgrade. However, to use the external 800K drive with the Macintosh 512K,
copy these three files:
1. System
2. Finder 5.1 or greater
3. Hard Disk 20
to your startup disk from the disk "Macintosh System Update for Macintosh
512K".