Here is a more in-depth explanation of the manual statement:
When using the Apple Tape Backup 40SC and Tape Backup 40SC 2.0.1 software to
do a "Volume" backup, be aware of several factors. The tape backup program
puts a "mirror" image of the hard drive onto the tape. In other words, the
backup software starts at sector 0 and continues reading to the end of the hard
drive. During this process, the backup software writes the data to the tape,
sector by sector; any and all bad sectors are written onto the tape as well.
This method of backup also copies information such as boot blocks, volume size,
and the volume directory.
When the "Restore Volume" command is selected, the software checks the tape for
the size of the volume it is going to restore. You are now prompted to select
the volume you want to have restored. At this point, the tape backup program
verifies that both volumes are exactly the same size. If the volume you are
restoring to is smaller than the volume on the tape backup, you get an error
message and the backup program won't allow you to continue. If the volume you
are restoring to is larger than the tape backup volume, you'll be able to
restore, but the volume will appear to be the same size as the original volume.
For example, after backing up a HD 20SC using the backup "Volume" option, then
restoring it to a HD 40SC, the HD 40SC will appear to have a total of only 20
megabytes of storage.
Different versions of the HD Setup program format Apple hard drives with
various amounts of total capacity. HD Setup 1.0 and 1.1 format hard drives
with the same number of blocks. HD Setup 1.2 give a different number than 1.0
and 1.1, while HD Setup 1.3 and 1.4 yield yet another different number of
blocks. The numbers of blocks also depends on the physical size of the disk
(e.g. 5.25" vs 3.5") or manufacturer.
Apple HD Setup 1.4 and later versions format all hard drives of like capacity
with the same number of blocks.
To locate a vendor's address and phone numbers, use the vendor name
as a search string.
Article Change History:
27 September 1993 - Revised, removing obsolete information and adding current
compatibility information.
5 November 1987 - Reviewed for technical accuracy.