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Whenever Apple II software writes a nibble, the virtual disk advances by 1/6,656 of a rotation.
Whenever Apple II software reads a nibble, it sees an alternating pattern of "no nibble yet" and a
valid nibble from disk, and when it sees a valid nibble, the disk advances by 1/6,656 of a rotation.
This means it is possible to read nibbles somewhat faster than from a real Disk II (where a valid
nibble is ready every 32µs).
Generally when the Apple II does not read or write any nibbles, the virtual disk does not spin. The
CFFA3000 virtual Disk II will not work with software that depends on:
The disk spinning while nibbles are not being read and written
The relative positions of data when seeking to another track
Seeking to half-track or quarter-track positions.
The Disk II emulation keeps one track at a time in RAM on the CFFA3000 card. When seeking to
another track, it writes the old track to the disk image if there have been any changes, and then it
reads the new track. If necessary, it automatically converts the track between sectors and nibbles.
The CFFA3000 uses its own slot-ROM code when booting, and it implements the $Cn5C and
related entry points for compatibility with the boot sequences of various operating systems.
Special Note: Formatting of Virtual Floppy Disks
Some as
pects of the CFFA3000 Disk II support make it such that ―formatting‖ of disks may not be
successful, depending on several factors:
Speed of the destination memory device
Operating system of the software doing the formatting
The formatting program itself
Several formatting scenarios have been tested with the CFFA3000, and the ones that have been
shown to work well are:
DOS 3.3‘s INIT command
Whole-disk copies as performed by COPYA (on the DOS 3.3 System Master diskette), which
performs a format operation before copying
Whole-disk copies as performed by , which performs a format operation before copying
Disk format operations performed by
ADTPro
Formatting scenarios that are known to NOT work are:
Formatting performed by the ProDOS system utilities
Formatting performed by the Apple Pascal Operating System
In general, all of these issues may be worked around by simply using a disk image that has been
created elsewhere with programs like
CiderPress
or
AppleCommander
.
