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Physical Format of Hard Disks
J-4
ERROR MAP
The error map (cylinder 0, sectors 0 and 12) is used to reallocate the next normal
track in place of a bad track. Sector 0 is the error map. Sector 12 is the back-up error
map.
The map is formatted as shown in Figure J-2. Each bit corresponds to a track on the
disk.
o
5
6 7
8
188
255
I
I
I
I
I
I
I
I
EIRIMIAIP
6.
I
I
I
I
I
I
I
I
Figure J-2 Error Map
NOC
C IC
I
C'
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
# : # : # I ERROR BIT MAP
o
III
2:
I :
I : : :
I
I
,
,
.......
.......
/
........
/
........
/
~
t
~
t
t : t : t
I
t
,
I
I
I
O~
1
2 :3
: 4 :
5
MSB
............
: t
:6
1
=
bad track
.............
: t
:7
LSB
o
=
normal track
L
Number of Cylinders
C#O - C#180: Cylinder No. 0-180
to - t7: Track No. 0-7
To reduce seek time, the system uses the track that immediately follows the bad
track for the reallocation. Figure J-3 demonstrates track reallocation.
UNU:EDI
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