Format A Track
After formatting each sector, the host must send new
values for C, H, R and N to the FDC for the next sector
on the track. The R value (sector number) is the only
value that must be changed by the host after each sector
is formatted. This allows the disk to be formatted with
The Format command allows an entire track to be
formatted. After a pulse from the IDX pin is detected, the
FDC starts writing data on the disk including gaps,
address marks, ID fields, and data fields per the IBM
System 34 or 3740 format (MFM or FM respectively).
The particular values that will be written to the gap and
data field are controlled by the values programmed into
N, SC, GPL, and D which are specified by the host during
the command phase. The data field of the sector is filled
with the data byte specified by D. The ID field for each
sector is supplied by the host; that is, four data bytes per
sector are needed by the FDC for C, H, R, and N
(cylinder, head, sector number and sector size
respectively).
nonsequential sector addresses (interleaving).
This
incrementing and formatting continues for the whole track
until the FDC encounters a pulse on the IDX pin again
and it terminates the command.
Table 28 contains typical values for gap fields which are
dependent upon the size of the sector and the number of
sectors on each track. Actual values can vary due to drive
electronics.
FORMAT FIELDS
SYSTEM 34 (DOUBLE DENSITY) FORMAT
DATA
GAP4a SYNC
IAM
GAP1 SYNC IDAM
C
Y
L
H
D
S
E
C
N
O
C
R
C
GAP2 SYNC
AM
C
R
C
80x
4E
12x
00
50x
4E
12x
00
22x
4E
12x
00
DATA
DATA
DATA
GAP3 GAP 4b
GAP3 GAP 4b
GAP3 GAP 4b
3x FC
C2
3x FE
A1
3x FB
A1 F8
SYSTEM 3740 (SINGLE DENSITY) FORMAT
DATA
AM
GAP4a SYNC
IAM
FC
GAP1 SYNC IDAM
C
Y
L
H
D
S
E
C
N
O
C
R
C
GAP2 SYNC
C
R
C
40x
FF
6x
00
26x
FF
6x
00
11x
FF
6x
00
FE
FB or
F8
PERPENDICULAR FORMAT
DATA
AM
GAP4a SYNC
IAM
GAP1 SYNC IDAM
C
Y
L
H
D
S
E
C
N
O
C
R
C
GAP2 SYNC
C
R
C
80x
4E
12x
00
50x
4E
12x
00
41x
4E
12x
00
3x FC
C2
3x FE
A1
3x FB
A1 F8
61
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