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Tape Transport
Read Back Checking
Full-Width Erasure
File Protection
Rewinding
3420 Models 4, 6, and 8
A single, direct-drive capstan moves tape forward or backward. Air bearings
reduce friction and tape wear since the oxide (recording) tape surface contacts
only the read/ write head, the erase head, and the tape cleaner. Short, tapered
vacuum columns greatly reduce tape inertia when starting and stopping tape. The
tapered columns and single-drive capstan start and stop tape quickly and
smoothly.
A two-gap read/ write head allows read back checking during a write operation.
Moving forward tape passes first the write gap, then the read gap.
An erase head applies a strong magnetic field that erases the entire width of tape
during write operations. Full-width erasure prevents interchangeability problems
when tape is written on one tape unit and read on another; it also reduces the
chances of leaving extraneous bits in interblock gaps or skip areas.
During a write, write tape mark, or erase operation, the tape unit monitors the
erase head operation. On a 3420 Model 4, 6, or 8 an erase head failure drops
tape unit ready status and halts tape motion. On a 3420 Model 3, 5, or 7 an
erase head failure sets
UNIT CHECK,
but does not drop ready status.
A write enable ring must be present in the file reel when writing. To avoid
destroying information on tape, remove the write enable ring. A reel without the
ring is "file-protected." The
FILE PROTECT
indicator remains on when a reel
without a file protect ring is mounted and no writing can occur.
Tape remains in the vacuum columns during rewind operations. Rewind ends
when a photocell senses a beginning-of-tape (load point) reflective marker on
tape.
During a rewind/unload operation, tape is rewound completely onto the file reel.
The tape unit is left in unloaded status, with the tape reel latch unlocked and the
window open, allowing the operator to remove the file reel.
The 3420 Models 4, 6, and 8 have the following added capabilities and features:
•
6250
BPI
capability.
•
0.3-inch
IBG.
Nominal data rates of 1250, 780, or 470 Kb/sec at 6250
BPI.
•
Improved access times.
•
Prec:1e motion control of the media to achieve faster data access times.
6250
BPI
or 6250/1600
BPI
density features.
•
Automatic read amplification.
New tape cleaning mechanism.
3420 Models 3, 5, and 7 can be converted to 3420 Models 4, 6, and 8.
10
3803-2/3420 Subsystem Description
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