Manual

June 2004 Isis® Sonar User's Manual, Volume 2

SEG-Y requires a 3200-byte EBCDIC record followed by a 400-byte binary header at the

beginning of the tape. Each trace starts with a 240-byte trace header followed by the

trace data. The three headers are all documented in SEGYFMT.H. If you do not find this

file on your Isis system, you can download it from our FTP site (no password needed).

The first 3200 bytes are written as a single block. This block is followed by a 400-byte

single block. (You must change block size to read the tape — this is required by the

SEG-Y specification.) When trying to read SEG-Y format, if the read software does not

change block size, then it will fail to read the data. Isis includes these blocks according to

specification.

As stated elsewhere in this manual, you can also use a “modified” SEG-Y format on

optical disks. The disk format is “modified” because of the difference in the types of

media: Tape access is sequential (“flat file”) whereas disk access is random. However,

the SEG-Y specification only accommodates sequential, flat-file access, so Triton Elics

has modified the SEG-Y format to work with disks.

Refer to

‘Setting Up Tape to Record or Play Back’ in the Isis User’s Manual,

Volume 1

, to see how to set up Isis for recording on tape.

C.4 Using Magneto-Optical Drives with Isis

Isis can recognize and use up to two multi-function magneto-optical drives if they are

logically attached to the SCSI controller as drives E: and F: in a DOS or Windows

environment. For 486-based systems, the SCSI controller is an Adaptec AHA 1542C (or

1542B, 1542CF); for Pentium-based systems, the SCSI controller is an AIC-7870 on the

CPU board. The two drives should be configured for SCSI ID numbers 5 (for drive E:)

and 6 (for drive F:). The M-O drives installed in an Isis system have large capacities (one

or more gigabytes per M-O) and can read from and write to several types of cartridges.

C.4.1 Different Sector Sizes, Different Purposes

Magneto-optical (“M-O”) cartridges come low-level formatted with either 1024-byte

sectors or 512-byte sectors. The 1024 size is typically used for UNIX systems, while

512-byte sectors are more common for Microsoft operating systems. Isis, which run

under Microsoft operating systems, expects to “see” (read) 512-byte sectors. Isis can

also read 1024-byte sectors if the M-O was high-level formatted for DOS, but

performance suffers: For an M-O low-level formatted at 1024-bytes per sector, Isis reads

the M-O at about 10% of normal.

Appendix C: Mass Storage Options