User Guide

Ampex 1308911-02 3-5
DD-2 Tape Format Instrumentation and Data Storage Recording
block sizes that are small or that divide (with their checksums) into 1,199,840 leaving only a
small remainder. For example, a data block size of 600,000 would waste almost half the space
in each physical block.
A second factor in choosing a data block size is that all transfers to/from the drive must be in
multiples of the data block size.
Byte-Stream Mode. Byte-stream mode allows data transfers of any length so long as they do
not start or end on an odd-byte boundary. Checksums are not used.
Note that byte-stream mode is not the same as variable-length records. Each byte is directly
addressable regardless of the number of bytes written at a time.
3.5 Instrumentation and Data Storage Recording
The DD-2 tape format provides an extend time stamp enable (ETSE) bit which determines
whether time code information is recorded with data written to tape.
When a DD-2 tape is formatted on a DIS tape drive operating in the instrumentation mode, the
ETSE bit is set to on to enable time code recording. The Ampex DST/DIS Tape Management
Software identifies this as the DIS format.
When a DD-2 tape is formatted on a DST drive or a DIS drive operating in the SCSI mode,
the ETSE bit is set to off to disable time code recording. The Ampex DST/DIS Tape
Management Software identifies this as the DST format.
Table 3-1 shows the read/write compatibility of DIS and DST formatted tapes on DST/DIS
tape drives. .
Table 3-1. DST and DIS Tape Format Compatibility
Tape Drive
DST Tape Format DIS Tape Format
Read Write Read Write
DIS drive operating in instrumentation mode Yes
1
No Yes Yes
DST drive or
DIS drive operating in SCSI mode
Yes Yes Yes Yes
2
1. Tape does not contain time code.
2. Invalid (zero) time code values are recorded for data written to tape.