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firebirdta84
March 12th, 2015, 12:46 AM
I'm just beginning my deep-dive into learning how the mid-late 1980s QIC tape cartridges were written with the distribution software (For Convergent Technologies & CTIX in particular).

From all indications I see, the logical end of tape (EOT) is marked with 2 consecutive filemarks (EOF marks).

In trying to re-create one of these original install tapes, I realize that I have no idea how to create this double filemark at the end.

In modern Linux, I can write the files doing consecutive dd if=FileNameXX of=/dev/nst0 commands (where the n in nst0 tells it not to rewind after writing).

However, when I try to just write a 0-byte file, I just get:

0+0 records in
0+0 records out
0 bytes (0 B) copied, .....

But the tape drives never moves to write another filemark.

Does anyone know how they did this back in the day?

Even if it can only be done on old UNIX or CTIX, I can try it on my running MightyFrame at least.

For now, I am using a Tandberg TDC-3620 with SCSI card, Linux distro:
Linux version 3.16.0-31-generic (buildd@akateko) (gcc version 4.9.1 (Ubuntu 4.9.1-16ubuntu6) ) #41-Ubuntu SMP Tue Feb 10 15:24:46 UTC 2015

...if that makes any difference...

Chuck(G)
March 12th, 2015, 10:05 AM
The mt untility has been in Unix for donkey's years. "mt weof 2" will write 2 filemarks. Note the use fo the environment variable TAPE or the optional /f argument that specifies where the tape is to be found.

firebirdta84
March 13th, 2015, 01:15 PM
Thanks, Chuck(G). I will experiment with that command as I progress.

I also sent a link to this post to my friend Tom (http://cholla.mmto.org/computers/mightyframe/), and he replied with an idea, that I will copy here for discussion:


The mt command was my first thought. You may not need to write two. My memory is that when you close the device, the tape writes two and then backspaces over the second one. This means that if you just rewind the tape, then you end up with the proper two filemarks -- but if you keep on writing another file, you get a single filemark since you write over the second.

I tested out his suggestion on my modern Linux setup, and indeed, it appears that the last file I write on the tape does have 2 filemarks, without me having to do anything special to create it.