Tandberg Data
Track, Tape format and Encoding Specification
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6-4
Tandberg SLR Reference Manual
6.3. Block Layouts
All blocks, whether it is a data block, a filemark block or a control block have the same layout.
6.3.1. Format-specific Block Layouts
Preamble
Block
Marker
Control
Field
(8 bytes)
Data
- - - - - - -
Data
(512 bytes)
CRC
(32-bit)
Postamble
Recording direction
Figure 6.3 Block layout – MLR3 (SLR50)/QIC-5010-DC/SLR6 (SLR24) formats
Preamble
Block
Marker
Randomizer
Seed
(3 bytes)
Control
Field
(8 bytes)
Data
- - - - - - -
Data
(512 bytes)
CRC1
(17-bit)
CRC2
(31-bit)
Pad
Field
Recording direction
Figure 6.4 Block layout – ALRF-1/ALRF-2/ALRF-6 formats
6.3.1.1. Preamble
The Preamble consists of a recording at a special pattern specified by the ALRF-1, ALRF-2,
ALRF-6, MLR3 (SLR50), QIC-5010-DC and SLR6 (SLR24) format specifications. The
Preamble is used to synchronize the VCO (Voltage Control Oscillator) in the read electronics
with the data frequency. Three preamble types are recorded:
Normal, Elongated and
Long
.
Normal Preamble
The Normal Preamble is recorded at the beginning of every block on the track.
Elongated Preamble
The Elongated Preamble is recorded at the beginning of the first block in a frame which is
appended to already existing data on a track, and to the first block in a frame after an
underrun situation. The Elongated Preamble is always followed by a Normal Preamble.
Long Preamble
The Long Preamble is recorded at the beginning of the first block on every track. The Long
Preamble will always be followed by a Normal Preamble.
6.3.1.2. Block Marker
The Block Marker identifies the end of the preamble and the beginning of the data field on
every block. It consists of a unique pattern described in the ALRF-1, ALRF-2, ALRF-6, MLR3
(SLR50), QIC-5010-DC and SLR6 (SLR24) format specifications.
6.3.1.3. Randomizer Seed
The randomizer is initialized, prior to receiving data, with a 24 bit seed, which is created from
a random process. The seed is recorded following the preamble and prior to recording the
data field, enabling the decoder to un-randomize the data field.