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2-6
Sector Format
Before writing in the data field, the
10
field must
be read to verify that the data is being written in
the correct sector. The recovery time from the
write operation to the read operation is too long
to allow writing of consecutive sectors because;
the channel requires time to stabilize. For this
reason, the sectors are numbered: 00, 30, 01,
31 ... 06, 36,07,37, etc, as shown in the
illustration.
Sector 06
Sector 36
Sector 07
Sector 37
110
I
Data
10
l
Data
10
I
Data
10
Recovery
Rd
I
Write
Recovery
Rd
ime
Time
T
VFO sync is 12 bytes of hex FF used to synchro-
nize the read clock with data bits from the disk.
When the 12 VFO sync bytes are being written on
the disk, the attachment forces 8 bytes of hex
FF, and then cycle steals the other 4 bytes from
a 10 byte field of hex FFs in storage.
Note:
If a sector defect occurs within the 10
region (VFO sync through the
10
field CRC),
this VFO sync is extended 64 bytes (12 plus 64
equals 76 bytes).
10
field is 7 bytes as described below.
Data
J
Write
I
I
,
\
\
\
\
"
"-
.........
- --
........
~
.....
m.;.;-..--~--
Data Tracks for Head 0
I ' " " " " T - ' T - -
Data Tracks for Head 1
60 Sectors On Each Track
........
----~~~
..............................
~
/ / '
"
/ ' / '
""
/ '
"-
/ '
"
~----/--
Identification buffer (lOB) is 1 byte (hex FF) of
/ '
space allowed after reading the
10
field CRC
/ ' / '
before switching the circuits from read to write.
/
,
, - - - - - - Start write gap (SWG) is 2 bytes of hex F F that " ,
allows time to switch the circuits from read to
"
write.
"
"
"-
"
Flag Byte: - - - - - - - - - - - - - - . .
Data Field
CRC Bfr 2 EWG
Bits
Meaning
7 Bytes
Unassigned
Data in sector has possible error
0-4
5
-
-----
3
4
5
6
7
00
Good primary sector
10
Defective primary sector
6-7 .
Flag Cylinder Head
Sector
eRe
Address Address Address
01
Good alternate sector
11
Defective alternate sector
The cylinder address is 2 bytes. _ _ ............... _ ..... _ _ _ _ _
- - - J
Disk
Cylinder
Capacity
Address
3.2 Megabytes (62GV)
I
0 to 108
5.0 Megabytes (62GV)
0 to 168
9.1 Megabytes (62TM)
0 to 302
13.7 Megabytes (62EH)
0 to 302
The head address is one byte; hex 00 for head 0, - - - - - - - - -..........
hex 01 for head 1, and hex 02 for head 2.
The sector address is one byte, 0 to 59. - ............... - -.....
------------1
CRC (cyclic redundancy check) is 2 bytes of
check characters to verify that the data was read
correctly from the
10
field.
t 4 - - - - - -
256 bytes
----1
Sync is 1 byte, hex OE, used to synchronize the
bit ring. The bit ring gates the bits read from the
disk into the serializer-deserializer to be formed
into recognizable bytes.
eRC (cyclic redundancy check) is 2 bytes of
check characters to verify that the data was
read correctly from the data field.
Buffer 2 (Bfr) is 4 bytes (hex FF) of space allowed
after writing the data field CRC before switching
the circuits back to read.
End write gap (EWG) is 2 bytes of hex FF t o - - - - - -
allow time to switch the circuits from write to
read.
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