Service bureaus (Was: Tek 4051 firmware listing

Jonas Otter jonas at
Mon Dec 20 03:14:02 CST 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.


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