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[ih] Impact of history on today's technology [was: why did CC happen at all?]

On 4 Sep 2014 at 23:23, John Day wrote:

> All Multics terminals were half duplex IBM Selectrix and it was 
> programmed in PL/1 that used EBCDIC.  But I will defer to Pogran on 
> this one.

You're referring to the IBM 2741.  I don't remember a lot but I once knew 
it VERY intimately because I hacked the code into the TIP to make it talk 
over the ARPAnet as if it were a regular full duplex ASCII terminal.

It was, indeed, a half-duplex, line-at-a-time Selectric.  When you typed 
a line of text and hit RETURN, it locked the keyboard until the other end 
sent something back and unlocked the keyboard.  It had interesting 
characters like circle-C and circle-D.  I think all the documentation on 
that stuff is long gone, alas.  There was some magic sequence you could 
send it that could unlock the keyboard, and so the overall sequence of 
events was something like get line of text, translate to ASCII, send out 
the connection, send the unlock the kbd sequence.   Something comes in 
from the other end: translate to EBCDIC, send the magic sequence to lock 
the keyboard, send the text out.

I believe that the ultimate test of that software [which wasn't real 
easy] was when I was able to log into TENEX from a 2741..... :o)


Bernie Cosell                     Fantasy Farm Fibers
mailto:bernie at fantasyfarm.com     Pearisburg, VA
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