A 128 can read & write to an 800K external drive. A 1.4 drive won't work. When I got my Mac in 1984, one of the first upgrades I made was to stick an 800K mechanism from an Apple][ into it. Worked like a champ. The 800K Apple][ drives were readily available, but 400K external Mac drives were scarce as hen's teeth.
You can sometimes get a HD disk to work in a 400K or 800K drive, but the disk will not hold its data for long. The lower density drives don't use enough write current to fully erase or magnetize the HD media.
You can sometimes get a HD disk to work in a 400K or 800K drive, but the disk will not hold its data for long. The lower density drives don't use enough write current to fully erase or magnetize the HD media.