3b5 tape driver question

[Theodore Hope]

I am writing some software which will ultimately run on an AT&T 3b5 (sVr2).
Part of this ordeal involves reading a tape written on a Big 'Ol IBM machine;
the tape has variable-length blocks of _up_to_ 6444 bytes.

 * I can read it on a Vax (4.2bsd): nc = read (fd, buf, 6444)

 * I can't read it on an AT&T 3b20 (sVr2): the mtc documentation (documentation,
   what documentation?) specifies that the largest possible read is 6144 bytes.


The abovementioned 3b5 is on the other side of the world, and I'd like to
know if anyone can tell me what the max read on the (raw) tape device is.
Is it 6144 (6k), or 8192?

Thanks in advance.
-- 
Theodore Hope
School of Information & Computer Science, Georgia Tech, Atlanta GA 30332
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