Weekly Classic Computer Trivia Question (20141205)

Jerome H. Fine jhfinedp3k at compsys.to
Tue Dec 9 14:01:14 CST 2014

 >Doug Ingraham wrote:

>Oh my!  I never expected to kindle a flame war (maybe it is rekindle).
>My favorite answer is "All of them."  If you assume a terrabyte is
AGREED!  However, you should really obtain some production figures
to justify that conclusion.

>1000000000000 bytes which is 10^12 and the smallest you could expect such a
>drive to be.  And also assume a DECtape (not DECtape II) has an unformatted
>capacity of 2700000 bits which is 337500 bytes.  So smallest drive capacity
I contend that the unformatted capacity of 337500 is completely
irrelevant since even if the unformatted capacity had been 10 times
that value, it would have made no difference in the number of bytes
written to the hard drive.  After all, the system reading the DECtape
received only the formatted result into memory (the hardware in the
controller probably did the reduction).  The same information would
then be written to the hard drive irrespective of the efficiency of the
method used to allow for errors when the DECtape was read and
the extra bytes in each sector or block were used to detect if an
error was present.

>and largest DECtape capacity would give at least 2962962 DECtapes.  Larger
>drives and smaller capacity tapes only increase this value.  We know that
>DECtapes used by OS/8 have usable capacity of 283008 bytes.  In that case
>it would be 3533469 tapes.      It is unlikely that even 2.9 million tapes
>were manufactured.
The number of DECtapes which were manufactured is really the
essential aspect of your (trick?) question.  I do agree that since
only a DEC user would have ever used a DECtape, less than
2.9 million tapes were ever made.  Can anyone who worked
at DEC confirm this?

I do apologize for starting the flame war when I provided my
description of the number of bytes in a terabyte, but that was
only to have a simple formula for the number of tapes whose
read contents (not the unformatted sectors) could be written
onto the hard drive.

Jerome Fine

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