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From: mitchalsup@aol.com (MitchAlsup1)
Newsgroups: comp.arch
Subject: Re: wisdom of the ancients, was Architectural implications of locate mode
 I/O
Date: Thu, 4 Jul 2024 15:04:37 +0000
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John Levine wrote:

> According to MitchAlsup1 <mitchalsup@aol.com>:
>>S.E.L created a thing they called the RCU (Remote Control Unit).
>>It was basically a channel with writable microcode. NASA bought
>>a bunch of them because they had tapes from the deep space radio
>>telescopes where an entire 9-track tape contained 1 record. NASA
>>just started the tape and recorded satellite data until the end
>>of the tape, where they would start the next tape just before the
>>end of the previous tape.
>>
>>So we programmed the RCU to read as much as the system memory
>>allowed, backed the tap up 1 second while dumping the data to
>>disk. Then we started the tape forward with the RCU watching
>>the pattern on the tape, when it detected 4096 bytes of the
>>last read, it would start streaming data in to memory again.
>>
>>No other company could demonstrate that they could read one
>>of those tapes.
>>
>>Presto, reading a whole 9-track tape with no inter record gaps !!
>
> That is pretty amazing.  Did NASA have a plan for reading
> those tapes, or did they not realize that normal tape units
> need record gaps, or what?


The satellite sending the data just sends a continuous stream
from up to 1 light hour away. So the original data had no IRG.
It might be the satellites were sending data at the fastest
rate the 9-track tapes could write and there was no time to
put IRGs on them.

{{It has been 40 years since I did some of that}}