Tandberg Data
Track, Tape format and Encoding Specification
___________________________________________________________________________
Tandberg SLR Reference Manual
6-7
6.4. Recording Methods
For ALRF-1/ALRF-2/ALRF-6, information is recorded on the tape using the RZ (RETURN to
ZERO) method where each change in the bitstream from 1 to 0 or vice versa is recorded as a
flux reversal. A continuous series of “0” bits or “1” bits give no flux transitions on the tape.
For older formats the information is recorded on the tape using the NRZ1 (NON-RETURN to
ZERO, change on ONEs) method where each “1” bit is recorded as a flux reversal. “0” bits
give no flux transitions on the tape, but are detected by measuring the distance between “1”
bits (flux reversals).
To avoid long distances on the tape without any flux changes (strings of “0” bits only), the
information to be recorded is encoded according to VR
2
RLL for ALRF-1/ALRF-2/ALRF-6,
RLL 1,7 for MLR3 (SLR50), QIC-5010-DC and SLR6 (SLR24), and GCR 0,2 rules for the
other formats.
6.4.1. Data Encoding; RLL 1,7 Rules
RLL 1,7 rules are
used for the SLR50/
QIC-5010-DC/SLR6
(SLR24) tape format
Prior to the recording of the data on the tape, the randomized data and control information
(plus the non-randomized CRC-bytes) will be transformed into an encoded bit pattern
according to the following table.
For each byte, the most significant two (four) bits will be encoded first, then the next two
(four) bits and so on.
The most significant data bit is always to the left in the table. The most significant encoded bit
is also to the left. When recording, the most significant encoded bit in each byte is recorded
first. The
x
denotes an encoded bit which is ONE if the preceding bit was a ZERO, but ZERO
if the preceding bit was a ONE.
This encoding method will give a minimum of one ‘0’ and a maximum of seven ‘0’s between
two ‘1’s.
Data Bits
Encoded Bits
Special patterns:
Eehex
1 1 1 0 1 1 1 0
⇒
Bbhex
1 0 1 1 1 0 1 1
⇒
Normal pattern:
0 1
⇒
1 0
⇒
1 1
⇒
0 0 0 1
⇒
0 0 1 0
⇒
0 0 1 1
⇒
0 0 0 0
⇒
0 1 0
0 0 0
0 0 1
0 0 1
0 1 0
0 0 0
0 0 1
0 1 0
X 0 0
0 1 0
X 0 1
X 0 0
0 0 1
X 0 0
0 0 0
0 1 0
0 0 1
0 1 0
0 0 0
NOTE:
If the two last bits of the last CRC-byte end with ‘00’, two additional bits ‘01’ will be added to the ‘00’-
bits before encoding. The encoded pattern is then followed by a normal postamble as usual.