Fujitsu M2488, Руководство по эксплуатации продукта

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TAPE UNIT SCSI COMMANDS M2488 PRODUCT GUIDE
4-78 CG00000-011503 REV. A April 1997
4-3.17.3 Description of Block ID Format
a. A 36 track tape consists of two interleaved groups of 18 tracks; each group is called a wrap. The first wrap is
written first and runs from Physical BOT towards Physical EOT. The second wrap is written second and runs
from Physical EOT towards Physical BOT. The tape unit hides the transition from the first wrap to the second
wrap so that the user sees an [abstract] continuous length of tape running from Logical BOT (the beginning of
the first wrap) to Logical EOT (the end of the second wrap).
BITS
BYTES 7 6 5 4 3 2 1 0
0 Wrap Physical reference
1 Format code Logical block position (MSB)
2 MSB
Logical block position
3 LSB
Table 4-72. Block ID Field Description
BYTE BIT VALUE DESCRIPTION
0 0-6
1-95 The Physical reference field will be in the range 1 to 95. The values in the range 1 to
95 indicate an approximate physical location on tape close to the target position.
0 7 0
1
The Wrap field indicates whether the target position is in the first wrap or second
wrap
a
of tape. If Wrap equals 0 then the target position is in the first wrap.
If Wrap equals 1 then the target position is in the second wrap.
1 6-7
The Format code field indicates the format of the tape cartridge. The meaning of the
possible values are shown in Table 4-73. When writing the format code reported will
be 01b (36 track, packeted.) When reading, the format code reported will be the format
code contained in the tape being read.
1
2-3
0-5
A unique Logical block position is associated with each data block and filemark writ-
ten on a tape. The first filemark or data block on tape is assigned Logical block posi-
tion 0; the Logical block position increases by 1 for each data block and filemark
thereafter. The maximum Logical block position is 3FFFEFh.
Table 4-73. Format Codes
FORMAT CODE VALUE FORMAT
00b 18 track, non-packeted
01b 36 track, packeted
10b 18 track, packeted
11b reserved