I also had a Mac Plus with an external 20MB hard drive (this was late 1988). It wasn't the Apple HD20 [0] (which I had never heard of until now) but a 3rd party model, it used the Plus's SCSI port and had the same footprint so it sat underneath. I see Apple also made an HD20SC that used SCSI.
I didn't understand walrus01's comment to mean an external, rather than internal, hard drive.
Comments
I also had a Mac Plus with an external 20MB hard drive (this was late 1988). It wasn't the Apple HD20 [0] (which I had never heard of until now) but a 3rd party model, it used the Plus's SCSI port and had the same footprint so it sat underneath. I see Apple also made an HD20SC that used SCSI.
I didn't understand walrus01's comment to mean an external, rather than internal, hard drive.
[0] https://en.wikipedia.org/wiki/Hard_Disk_20