by Darius Kazemi, July 2 2019

In 2019 I'm reading one RFC a day in chronological order starting from the very first one. More on this project here. There is a table of contents for all my RFC posts.

Character correspondences

RFC-183 (PDF) is titled “The EBCDIC Codes and Their Mapping to ASCII”. It's by Joel Winett of MIT Lincoln Laboratory and dated July 21, 1971.

The technical content

In 1971 the two most popular character encodings on ARPANET are ASCII and something called EBCDIC, the Extended Binary Coded Decimal Interchange Code. It's a character encoding invented by IBM and used on many of their systems, including a large minority of ARPANET sites.

There are characters that are represented in EBCDIC (like the “¢” symbol) that have no equivalent in 128-bit ASCII, and vice versa. These conceptual overlaps and mismatches were already discussed in detail in my RFC-110 post since it was about getting an IBM terminal to speak correctly to ASCII systems.

The author provides three different methods of substituting characters that can be used when one type of system is corresponding with the other type, and there is an attached questionnaire asking readers to reply with their favorite of the conversions. The idea is to eventually standardize this.


The first set of character correspondences is one recommended by IBM, and it's frankly weird to me! For example, it recommends that the ASCII symbol for ! (exclamation mark) be used as a stand-in for the EBCDIC ¡ (the upside-down exclamation mark). But the author notes that this means that “another code must be used to represent” the exclamation mark. Uhhh okay??

Anyway I haven't looked ahead but I hope that the IBM-style correspondence doesn't win the survey...

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About me

I'm Darius Kazemi. I'm an independent technologist and artist. I do a lot of work on the decentralized web with ActivityPub, including a Node.js reference implementation, an RSS-to-ActivityPub converter, and a fork of Mastodon, called Hometown. You can support my work via my Patreon.