Sector Format; Logical Vs. Physical Sectors; Surface Mode Vs. Cylinder Mode - HP 7925D Service Manual

7925
Theory of Operation
~INDEXZONE
~
SECTOR
0 63 62 ....
PHYSICAL
LOGICAL
0 63
62
62 61
61 60
60
59
59 58
T
2
2
OF~I~~~i:g~
- - - - - - - -....
3
3
2
o
3
4
.... 4
3
4
o
H
~
2
D
7311-34
Figure 1-3. Logical vs. Physical Sectors
~
SECTOR 0,1, 2 ...
SECTOR ... 61, 62, 63
~
TRACK N
TRACK N
+
1
TRACK N
+
2
SURFACE MODE
SURFACE
~CYllNDERN
j
CYLINDER N + 1
HEAD
~
, CYLINDER N
+
2
t
I I
I
I
0
I
I
L:J
DATA
1
L:J DATA
2
I
I
I
I
L:J
DATA
3
L:J
DATA
I
I
SERVO
I I
L:J
SERVO
4
L:J
DATA
I I
5
I I
L:J
DATA
6
L:J
I I
DATA
I
I
L:J
DATA
8
CJ
DATA
CYLINDER MODE
7311-35
1-6.
SECTOR FORMAT
Figure 1-4. Surface Mode vs. Cylinder Mode
which specifies the head and sector addresses and provides
the spare, protected, and defective track status indicators.
The smallest addressable data storage area on a data
surface is a data sector (see figure 1-5). Accessing a data
sector is accomplished when the controller specifies the
address of the cylinder, head, and sector. Each data sector
contains a 15-word preamble, a 128-word data field, and a
7-word postamble.
The data field is used to store 128 words of data. Each
word is defined as being 16-bits. Only the data field is
transferred to and from the system during most data oper-
ations. The preamble and postamble are normally gener-
ated and checked by the controller.
The 15-word preamble is used for synchronization and
addressing purposes. It is comprised of a 12-word sync
field; a sync word; a cylinder address word; and a word
The 7 -word postamble consists of a cyclic redundancy
check word and six words of error correction code. The
controller generates this check information during a write
1-3