> We have both models, DLT4000 and DLT7000. The DLT7000 can read the
> DLT4000 tapes; however, the reverse is not true. The DLT4000
> canNOT read the
> DLT7000 tapes.

From Quantum's on-line manual for the DLT7000:
"To select density on the tape drive:
   1. Load the tape cartridge into the tape drive.
      The amber Tape in Use LED blinks while the tape
      loads and calibrates.
   2. After calibration is complete, the Tape in Use
      LED remains steadily lit. The appropriate tape
      density LED along the left edge of the drive's
      front panel lights to indicate the tape's
      prerecorded density (if any), such as 2.6 GB
      or 6.0 GB.
   3. Use the tape drive's density Select Button to
      select the desired density, if different than
      that indicated by the lighted tape density LED.
      Density selection is inactive until a WRITE from
      BOT is issued. The controller retains the selected
      density until 1) the density selection is changed,
      or 2) the tape is unloaded."

The media used determines the default density and available alternate
densities. A DLT IV defaults to 35/70, and can be overridden to 20/40;
a IIIxt can only be used at 15/30; a III defaults to 10/20, with
alternates of 2.6 and 6.

Density can also be controlled by the host. If HP is using a MODE
SELECT (SCSI command) to force the drive to use its maximum density
(or to reset it to the default for the media present), that's their
choice; a DLT7000 is perfectly capable of writing tapes that can be
read on a DLT4000 (or a DLT2000).

Trivia note: the bit density of the original DLT, a 10GB DLTIII or a
15GB DLTIIIxt, is 62500 BPI. Coincidence? Maybe...


Steve Dirickson   WestWin Consulting
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