IBM 1620 invalid character symbol

Ken Shirriff via Unicode unicode at
Wed Sep 27 17:48:17 CDT 2017

More information from Tim Coslet of the Computer History Museum 1620 Team:

The Model I printed a Cyrillic Ж for invalid character codes.
The width of the Cyrillic Ж was narrower than shown at left, so that it
matched the width of other characters the typewriter typed.
The Model II printed a character called "pillow" for invalid character
codes. "Pillow" was a solid black rectangle.

Ken Shirriff (the other Ken)

On Wed, Sep 27, 2017 at 1:36 PM, Ken Shirriff <ken.shirriff at>

> 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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