800K floppy drive with Mac 128K/512K?

[bigmessowires]

Does anyone know if you can use an 800K floppy drive to read 400K disks with a Mac 128K or 512K (the ones with 64K ROM)? I know those machines can't read 800K disks, but can they read 400K disks from an 800K drive? Anyone have the necessary hardware to try it?

I'm trying to determine if my floppy emulator needs to emulate a 400K *drive*, or only a 400K disk in an 800K drive, to work with those Macs.

 

[bbraun]

Yes, a 400k disk written from an 800k or even 1.4MB drive will be fine. By default, macos will write MFS to 400k disks, and you have to do some contortions to make it write HFS to 400k.

The 64k ROM machines can use an 800k drive (and HFS) if you load the HD20 init.

 

[bigmessowires]

Thanks. We may be talking about slightly different things, however. I was wondering about the compatibility of the drive itself rather than the media. I.e. can you connect a M0131 external 800K drive to a stock Mac 128K or unenhanced 512K, and expect it to work, as long as you only read/write 400K MFS disks?

Thinking about it further, the answer must be yes, otherwise there would be no way to load that HD20 init.

That's good news, as it means my floppy emulator can identify itself as a double-sided drive in all cases, and the 128K/512K will just ignore the second side. Of course it will only work if you select a 400K MFS disk image.

 

[waynestewart]

Made me curious. Got out my 128k Mac for first time in about 18 months I think and plugged an 800k drive into the floppy port. Put a 400k disk into it and booted off it.

Then I tried formatting a disk in the 800k drive but no go.

I thought maybe it's the drive and when I grabbed another, I accidentally grabbed a Superdrive. It won't read any disk or successfully format one.

Got out anther 800k drive and it also won't format a disk. Moved my system disk to it and formatted on the internal 400k. Afterward I could move the formatted floppy back to the 800k drive where I could read and write to it.

I've used Superdrives on Macs and Apple IIs in place of 800k drives and they were always seen as 800k drives. Finally found an exception. I'll have to make sure I don't upgrade all my external 800k drives.

 

[bigmessowires]

Interesting! So the external 800K drive works ok for reading 400K disks with the Mac 128K, but not for formatting those disks? What kind of error did you get when you tried to format a disk, and how far into the format process did it get? Did you try doing any plain old writes to the 400K disk, copying files, etc?

 

[Anonymous Freak]

On my 128K-with-512K-motherboard, I can use a later 800K floppy drive just fine with 400K disks.

I'll try formatting when I get home - I doubt I'd ever tried that, likely just used the internal to format.

 

[waynestewart]

I tried several disks in two 800k drives. When I tried to format the drive would whir for less than a second and display the message "Initialization failed !"

After formatting a disk in the internal 400k drive, I moved it to the 800k and was able to read and write to it.

I was using Finder 1.1

 

[bigmessowires]

Huh, well that's odd. I guess I'll just have to wait and see if my emulator can initialize virtual floppies with the 128K/512K or not. It sounds like it's not an issue with how the drive identifies itself to the Mac, since reads and normal writes work just fine. It must be some kind of timing-related or disk RPM thing.