Am 06.06.2013 19:22 schrieb slickrcbdnews@gmail.com:
So, were they single density or double density drives?
Woz used GCR, which is comparable to double density (the technical word is "modified frequency modulation", MFM).
Did single-density disks even exist,
No. This is marketing gibberish. A FM signal consists of a clock bit and a data bit, a MFM signal uses combined clock and data bits and stores two of them in the same area. So from the magnetic disk's point of view there is absolutely no difference.
Patrick