(from the Windows Administrator's Guide, page 134)

IBM 3494 tape categories

Typically, a software application that uses a 3494 library uses volumes
in one or more categories that are reserved for that application. To
avoid loss of data, each application sharing the library must have
unique categories. When you define a 3494 library to the server, you can
use the PRIVATECATEGORY and SCRATCHCATEGORY parameters to specify the
category numbers for private and scratch Tivoli Storage Manager volumes
in that library. If the volumes are IBM 3592 WORM (write once, read
many) volumes, you can use the WORMSCRATCHCATEGORY parameter to specify
category numbers for scratch WORM volumes in the library. See "IBM
Tivoli Storage Manager Volumes" on page 79 for more information on
private, scratch, and scratch WORM volumes.

--
Mark Stapleton (stapleton AT berbee DOT com)
Office 262.521.5627