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SYNC 1
08
CHECKSUM
SECTOR
TRACK
lOl, lO2
GAPI
SYNC 2
07
BYTEO, BYTEI
DATA
CHECKSUM 2
GAP 2
-
40 bits of ones (all l's is the highest write frequency).
-
Disk I.D. field identification mark.
-
Checksum of lO 1, lO2, SECTOR, TRACK.
-
The number of this sector
-
Track which this sector resides on.
-
2 bytes (20 bits) indicating the diskette I.D. (the I.D. is
specified by the user when the diskette is formatted).
-
72 bits of GCRO or 010 10 10 1 (8 bit byte
x
9)
-
40 bits of ones.
-
Disk data field identification mark.
-
Track and sector of next related block.
-
254 bytes (2540 bits) of data.
-
Checksum of BYTEO, BYTEI,andDATA.
-
Variable gap of GCR O. This gap is variable depending on the
speed of the disk during format. GAP 2 will be constant for all
sectors except for the tail gap (the gap between
I
st and the
last sectors).
1551 Format: Expanded View of a Single Sector
1551 BLOCK DISTRIBUTION BY TRACK
Track number
Range of Sectors
Total # of Sectors
I
to 17
18 to 24
25 to 30
31 to 35
BYTE
CONTENTS
0,1
18,01
2
65
3
0
4-143
%
1
=
available block
o
to 20
o
to 18
o
to 17
o
to 16
1551 BAM FORMAT
Track
18,
Sector
O.
DEFINITION
Track and sector of first directory block.
21
19
18
17
ASCII character A indicating
1551/4040
format.
Null flag for future DOS use.
Bit map of the available blocks in tracks 1-35.
%0
=
block not available (each bit represents one block)
78
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