Magnetic Tape Reel

This is 1/2" wide, 2400ft long, 9 track magnetic tape reel.
About 12ft of tape is unreeled to expose the BOT (Beginning Of Tape) reflective strip.
It is stuck at the front edge. A light shining at an angle is reflected to photo-electric
cell that triggured a stop to the tape movement.
(Hence the prohibition of flash photography of the drives.)

There was a similar reflective strip 12ft from the end of tape stuck at the back edge
that signalled the End Of Tape and last block to be written.

The reel is out of its self-loading collar. When in its collar all that the computer operator
had to do was place the reel on the hub and press the LOAD button when the drive automatically
threaded the tape to the take up reel and wound it on a few turns, then air pressure sucked
the tape into the vacuum columns and the capstan moved the tape till the BOT was detected.
The whole loading process took about 10 seconds.

At fullsize the label on the reel can be read, albiet upsidedown.
On it is the volume serial number T0014T and the rack number T014.
The volume serial number is magnetically written on the tape and is checked by the
Operating System when the tape is mounted.
The rack number is where the tape is stored when not in use. This tape was a backup tape.

Before 1960 disk drive storage was in its infancy and data storage was on magnetic tape.
A program might read data from a magnetic tape, process it and produce a printed output.
Or a program might read data from paper tape and the magnetic tape,
process both and write the results to another tape that became the input for the next process.
(As in a payroll application.)

By 1980 most data stored on computers was stored on disk drives.
Magnetic tape was just used to store backup copies of disks.