The Bad Track Table - AT&T 6300 Service Manual

DIAGNOSTICS
The Bad Track Table
The Bad Track Table (BTT) is a table in memory that stores
information on bad tracks, obtained from the Verify Surface Test
and from information manually inserted by the user.
If the "FORMAT BAD TRACKS" option or option 1 of "DISPLAY
AND EDIT BAD TRACK TABLE" is selected, (the following
sections describe these functions) all the tracks stored in the BTT
will be physically reformatted with the "bad track flag" bit set in
the ID field of each sector. The reformat of each bad track is
verified and retried once, if all the sectors in the track fail to
return codes. If the verification fails after the second reformat, a
failure message is printed.
• This BTT is cleared when the utility is loaded and is never
cleared while the utility is running.
• Bad tracks will not generate error messages unless the
number of bad tracks exceeds the maximum permissible
number. The maximum permissible number is:
a. Either 64 bad tracks total, or 2 bad tracks per megabyte
of formatted storage, whichever is larger. In other
words, the magic number is 64 for storage up to 32 MB
and 2N megabyte/megabyte for higher storage.
b. Cylinders 0, 1, 2, and 3 must be error free.
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