V3/usr/man/man4/tc.4

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including files from this version of Unix. 
.pa 1
.he 'TC (IV)'3/15/72'TC (IV)'
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NAME		tc -- TC-11/TU56 DECtape
.sp
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DESCRIPTION	The
files tap0 ... tap7 refer to the
TC-11/TU56 DECtape drives 0 to 7.
Since the logical drive number can be manually set,
all eight files exist even though at present there are fewer
physical drives.

The 256-word blocks on a standard DECtape are numbered 0 to 577.
However, the system makes no assumption about this number;
a block can be read or written if it exists on the
tape and not otherwise.
An error is returned if a transaction
is attempted for a block which does not exist.

Addressing on the tape files, like that on the
RK and RF disks, is block-oriented.
.sp
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FILES		/dev/tap?
.sp
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SEE ALSO	rf(IV), tap(I)
.sp
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BUGS		see rf(IV)