The Apple SuperDrive is a disk drive that can read and write in the standard
Macintosh 400K and 800K formats, as well as the newer 1.4MB format. It also
allows reading and writing 800K Apple II ProDOS, 720K MS-DOS, and 1.44MB MS-
DOS formats.
(NOTE: The format used for MS-DOS is the same one used by OS/2.)
The SuperDrive uses 3.5-inch disks. These disks are available from several
sources and come in three "flavors": single-sided (400K), double-sided
(800K), and high-density (1.4MB). As a rule, the various disk types are
guaranteed by the manufacturer to provide a certain level of storage per disk
with little or no errors at the rated storage capacity.
The single-sided disk can be formatted to 400K, and the double-sided disk
can be formatted as 800K with confidence (it can also be formatted to
400K). If you do format the 800K disk as a 400K disk, you lose about
one-half of the disk's actual rated storage capacity. This may be useful
if you want to pass data to a friend who has a Macintosh 512K or a
Macintosh XL, which can read only 400K disks. You do not need to buy 400K
disks -- just use your 800K disks formatted as 400K.
(Many single-sided disks are really double-sided disks that did not pass the
factory's stringent testing standards for double-sided media, but passed as
single-sided disks. So, other than the guarantee from the manufacturer,
double-sided and single-sided disks are manufactured with the same process.
High-density disks, however, are manufactured with a completely different
process [different oxides, different rating of magnetic flux capacity per
square inch, and so on].)
If you have a Macintosh that does NOT have the FDHD capability (like a
Macintosh Plus), it is possible to take the high-density media and format
it as a 400K or an 800K disk, but is NOT supported.
Unlike the double-density disk (800K), which can be formatted as 400K and be
guaranteed to work as a 400K disk, there is no guarantee (especially from the
manufacturers of the disk media) that the high-density (1.4MB) disk, when
formatted as a 800K or 400K, will work as flawlessly as the user might expect.
The high-density media is a completely different media than is used in the
single-sided and double-sided disks. Even the process to read and write
information to the 1.4MB disk differs from the 400/800K modes of disk
operation. A Macintosh configured for a SuperDrive as one of its floppy
drives can tell the difference.
IMPORTANT NOTE: The Macintoshes that support SuperDrives include:
- Macintosh IIx
- Macintosh IIcx
- Macintosh SE/30
- Macintosh SEs sold after August 2, 1989.
This article is continued in "Apple SuperDrive: User Guide (Part 2 of 3)".