Weekly Classic Computer Trivia Question (20150121)
dpi at dustyoldcomputers.com
Thu Jan 22 00:27:37 CST 2015
Many of us on this list are collectors of one sort of computer or another.
I don't think of myself as a collector so much as a caretaker of my PDP-8.
Of the things it has been fairly easy to get in recent years are the CPU
and its related cards for the models that were produced in fairly large
numbers. What is not easy to get are peripherals for these machines. So
here is a question relating to the Type 750 high speed paper tape reader
found on the early models. A few years back we were working on getting the
CPU back in good working order. We needed to read in the diagnostic paper
tapes but the reader was not reliable. Went through the tuning procedure
and found that it was trying to read the tape at nearly 450 cps. After
tuning it up the full speed now sits at 342 cps.
The question is how many frames does it have to read before it reaches full
This is probably a somewhat squishy number and would depend somewhat on
tuning. I wrote a couple of programs to determine this so I could add
correct delays to my emulator. I was able to obtain a 3 microsecond
resolution count of the delay. How that was accomplished might make for
another trivia question.
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