Table of Contents
Advertisement
Chapter 1. The IBM 3480 Magnetic Tape Subsystem
The IBM 3480 Magnetic Tape Subsystem consists of a 3480 Control Unit,
Model All or A22, and up to four 3480 Tape Units, Model Bll or B22. Each
tape unit contains two magnetic tape drives. With a Dual Control Unit
Communications Coupler feature, two control units can be connected to
allow mutual control of eight tape units (16 drives). The Automatic
Cartridge Loader feature, which allows both the automatic loading of
premounted tape cartridges and the manual loading of single tape
cartridges, can be added to any or all of the tape units. With additional
channel attachment features, each control unit can connect with up to four
channels.
The subsystem can read and write data at rates up to three megabytes per
second. This high data rate is achieved by recording 18 data tracks at a
linear data recording density of about 38000 bytes per inch.
The control unit contains a buffer that stores the data being transferred
between the tape drive and the controlling processor. The buffer reduces
delays in the operations of the processor that are normally caused by the
start and stop actions of individual drives. Because of the buffer, blocks of
data to be written are transferred to the control unit before the tape drive
is ready to accept them. The channel is then released to do other work
while the data transfers from the control unit to the tape drive. During
reading, data is transferred from the tape drive to the control unit buffer so
as to be available when the controlling processor requests it.
Because the 3480 subsystem indicates that the writing action is complete as
soon as the write data has been transferred to the buffer, the subsystem also
provides a tape-write-immediate mode of writing data to tape.
Tape-write-immediate mode forces the subsystem to write the data on the
tape before it indicates that the action is complete. Tape-write-immediate
mode should be used only when the data is critical because this mode
reduces subsystem performance.
The 3480 subsystem provides a high-speed search function. With high-speed
search, you can search for specific blocks on the tape (with the subsystem
disconnected from the channel) at much higher speed than is used for
reading and writing. When the block is found, the subsystem reconnects to
the channel to signal that it is ready for the next command.
Each tape drive has a message display on its operator's panel. The
messages on this display can keep the operator informed of the status of the
tape drive. In an MVS system, the program can write any necessary
messages to the drive message display.
Chapter 1. The IBM 3480 Magnetic Tape Subsystem
1
Hide quick links:
Advertisement
Table of Contents
