5190/5194 Modular Tape Subsystem Manual

Introduction to the Modular Tape Subsystem
5190/5194 Modular Tape Subsystem Manual—426878-002
1-5
Labeled and Unlabeled Tapes
will occur if an application attempts to read or write. Table 1-2 summarizes 5190 and
5194 cartridge tape compatibility.
Labeled and Unlabeled Tapes
The modular tape subsystem can use both labeled and unlabeled cartridge tapes. A
tape label is a record at the beginning of a tape that identifies the tape volume and the
files it contains. An expiration date protects labeled-tape information from being
accidentally overwritten. A scratch tape is a labeled tape with an expiration date that
has passed. If a tape has no standard label, it is considered unlabeled.
You should use labeled tapes with the modular tape subsystem because they can be
cataloged and offer security features for protecting data.
The operating system supports two standard tape-label formats:
•
ANSI
•
IBM-MVS
For information about labeled-tape operations, see Using the MEDIACOM Utility for
Labeled-Tape Operations on page 4-42.
Data Compression
The 5190 tape drive can write compressed or uncompressed information to labeled or
unlabeled tape. The 5194 tape drive always operates in compression mode.
Compression can increase cartridge capacity typically by a factor of two. Compression
is further described under Controlling Data Compression (5190 Tape Drive) on
page 4-44.
The 5190 and 5194 drive CRUs write and read tapes that are compatible with the IBM
3480 and 3490 Improved Data Recording Capability (IDRC) compression format.
IDRC is a data compression technique that lets you to store more data on each
cartridge.
Writing compressed data on tape is the only mode of the 5194 tape drive, which means
the tape drive compresses data whenever possible. When using the 5194 tape drive
(assuming you use an extended tape and compression for the first time), you can store
much more data than on a 5190 tape drive.
The exact amount of data stored on tape is not predictable, because the amount of
compression varies with the data being written. Because the amount of compressed
data stored on tape can vary significantly, some comparisons between the 5190 and
Table 1-2. 5190 and 5194 Cartridge Tape Compatibility
Tape
Drive
Read 18-Track
Format
Write 18-Track
Format
Read and Write 36-Track Format
on Standard and Thin Tape Media
5190 Yes Yes No
5194 Yes No Yes