IBM 1620 invalid character symbol

Ken Shirriff via Unicode unicode at
Wed Sep 27 15:36:55 CDT 2017

I checked with the Computer History Museum about the 1620. According to Dave
Babcock, IBM 1620 Restoration Team Lead at the CHM:

The 1620 console typewriter actually had a "zha" character typebar that
it would use for unknown characters.

The only overprinting that the typewriter would do was a "flag" mark [an
"overscore" rather than an "underscore"] and a center-hyphen [used for
characters with bad parity].  For both of these, it would first print
the special character [flag or center-hyphen] without advancing the
carriage, then print the other digit or alpha character.

And yes, it was possible to get a "bad parity unknown character" which
would print the center-hyphen and zha.

The typewriter was not capable of backspacing to do any other overprinting.

With the Wheelwriter-based console typewriter that we're using for the
IBM 1620 Jr. we will be doing some real print-backspace-print
overprinting to approximate some of the special characters, like zha.

Ken Shirriff (the other Ken)

On Mon, Sep 25, 2017 at 9:48 PM, Leo Broukhis via Unicode <
unicode at> wrote:

> Wikipedia (
> describes the "invalid character" symbol (see attachment) as a Cyrillic Ж
> which it obviously is not.
> But what is it? Does it deserve encoding, or is it a glyph variation of an
> existing codepoint?
> The question is somewhat prompted by
> in the pipeline, although I learned about both earlier today within a few
> minutes of one another.
> Thanks,
> Leo
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