
The Evolution of Character Codes, 1874-1968 [pdf] - dang
http://trafficways.org/ascii/ascii.pdf
======
iconjack
Enjoy this character code puzzle.
[http://realmode.com/punch22.html](http://realmode.com/punch22.html)

~~~
nickysielicki
I've been thinking about this all night. I can't seem to wrap my head around
it. Got a hint for me?

~~~
KMag
It's not possible if they want to be able to over-punch their current stock of
5-bit punched used tapes. Proof: take for instance the character U. U has 4
holes, leaving 3 unpunched spots, which means 7 possibilities for modification
(2^3 - 1 = 7). Those 7 possible modified Us must cover all of the 25 non-U
letters.

We can assume then that it's not a requirement to be able to over-punch their
existing used 5-bit punched stock. Then it's possible, and my proof above of
why it's not possible to convert a 4-hole U to more than 7 other characters is
a big hint as to one solution... think of a primary encoding and a secondary
encoding. What property must the primary encoding have in order to guarantee
any character in the primary encoding can be over-punched to one of 25
characters in the secondary encoding?

------
dang
Via
[https://news.ycombinator.com/item?id=11093735](https://news.ycombinator.com/item?id=11093735).

