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Technical Notes
Applications
Most applications will use the default volume or will
name a volume when accessing a file. No special Mac
Disk handling is required from applications that
use
volumes this
way.
Applications which eject disk volumes
should be written
so
that they can gracefully handle
an
elTOr return if they attempt to eject a Mac Disk volume.
The application
can
check to see if a drive is ejectable by
calling the Mac Disk driver (see Ma9
Disk Characteristics
below).
Mac Disk Characteristics
Davong's Mac Disk is a block -oriented device handled
by the Macintosh file system. To bypass the file system
and talk directly to Mac Disk, call the Mac Disk driver via
the Device Manager read and write traps
I
specifying the
drive· number of the volume you want to access.
The driver is always open.
It
supports calls to read
and write one or more sequential 512-byte blocks of the
disk. (The Mac Disk does not support file tags; therefore
your I/O request is truncated to a 512-byte multiple.) You
can only access the disk space of volumes that can be
read by the Macintosh operating system.
The disk driver is loaded from SYSTEM.RSRC at boot
time. It is a reSOlU"ce of type DRVR named
.'Mac Disk.
The Davong disk driver occupies about 2K bytes of the
system heap. The driver refnum, resource
10,
and size
are all subject to change.
Mac Disk resident volumes are identical to
diskette~based
volumes with two exceptions:
•
Volumes are not ejectable
•
Version
l~lg
of the Finder does not 'vvrite out boot
block data to nondiskette devices; therefore, copying
a system file from a Mac Disk
volume
to diskette
does not produce a boatable diskette.
C-2
~
Copyright 1985 Davong Systems,
[nco
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