Service bureaus (Was: Tek 4051 firmware listing - test-drb@ccmp.vtda.org

20 Dec 2010

...
  And I have a model 33 teletype here, with some
provenance claiming an
 IBM lineage, that has a slashed-oh between the I and the P keys and an
 unslashed-zero next to the 9 key.

 Pressing the slashed-oh, sends 0x4F and pressing the unslashed-zero
 sends 0x30... and conversely, it prints an unslashed-zero when 0x30 is
 sent to it and it prints a slashed-oh when 0x4F is sent to it... 
I just borrowed a book from 1974 about JCL by a person who had worked as
a systems programmer at IBM. In his coding examples, he consistently
puts a slash through the Ohs and leaves the zeroes unslashed. I would
assume therefore that that was standard practice for IBM mainframe work
at that time.

/Jonas