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In the early history of computing before the mid-1960s, there was no universal, de-facto standard for the written representation of a hexadecimal number, different computer systems used their own written presentations. Wikipedia has some examples.

  • The ILLIAC I (1952) computer used the uppercase letters K, S, N, J, F and L for the values 10 to 15.

  • The Honeywell Datamatic D-1000 (1957) used the lowercase letters b, c, d, e, f, and g whereas the Elbit 100 (1967) used the uppercase letters B, C, D, E, F and G for the values 10 to 15.

  • The Monrobot XI (1960) used the letters S, T, U, V, W and X for the values 10 to 15.

  • The Pacific Data Systems 1020 (1964) used the letters L, C, A, S, M and D for the values 10 to 15.

I was reading alt.folklore.computers today and found a claim: The IBM S/360 was one of the major computer systems that used 'A' to 'F' to represent a hexadecimal number, and S/360 was largely responsible the popularization of this de-facto standard due to its success.

How true is this claim?

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    Wasn't A, B, C, D, .... universally used in mathematics for digits in positional bases above 10? See e.g. Egmont Colerus: Vom Einmaleins zum Integral from 1934.
    – Radovan Garabík
    Jun 6, 2020 at 12:41
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    @RadovanGarabík: I've seen a variety of notations for digits above nine, especially when using things like base 11 or 12 (which just need one or two extra symbols) or base 20 (which sometimes used normal and altered forms of digits 0-9). No doubt people have used A-F to represent digits with values 10-15 for a long time, but older papers I've seen that talk about number bases always seemed to regard the choice of digits as arbitrary, rather than suggesting that there was a standard convention.
    – supercat
    Jun 6, 2020 at 17:14
  • Gotta say your research is excellent.
    – zarchasmpgmr
    Jun 7, 2020 at 1:16
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    @RadovanGarabík What is Mathematics by Courant & Robbins (1941) uses lower case Greek letters. There seems to have been no standard notation in the way there is today.
    – Michael Graf
    Jun 8, 2020 at 14:35
  • I gotta say, if I needed a symbol for each of 10, 11, 12, 13, 14 and 15, then ABCDEF are the first I'd think of. Even BCDEFG seems like a strange choice, unless maybe they had reason to skip A. But who on earth came up with KSNJFL and LCASMD and why?
    – Omar and Lorraine
    Oct 27, 2022 at 8:43

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TL;DR:

How true is this claim?

It's true. While others used it before, it was the success of the /360 making it the default way around the industry.

The long read:

[Preface: I love the shown research]

I was reading alt.folklore.computers today and found a claim: The IBM S/360 was one of the major computer systems that used 'A' to 'F' to represent a hexadecimal number,

True. While A-F has been used before, it didn't get much used as architectures were largely based around word sizes with a multiple of 3, making octal the best representation.

One major goal for the /360 architecture was fast (and easy) handling of decimal data without much conversion. For that byte (and word) size as multiples of four is the most obvious and storage efficient size. With an 8 bit byte two (numeric) punch card columns can be stored in one byte, 7 to a word and 15 to a double word (plus sign). As a result they needed symbols for the remaining six combination and went for A-F.

(Also, on a side note, the /360 was not simply 'one of' the 'major computer systems' but has essentially blown everything else away)

and S/360 was largely responsible the popularization of this de-facto standard due to its success.

Exactly. IBM did bet it's company on the /360 and won. Right after introduction it became an incredible success, making IBM the IT giant it has been thruout the 70s and 80s. It became the de facto architecture for mainframes, sucking in everyone able to spell at least two letters of C/O/B/O/L in arbitrary order as programmer. All manuals and training documentation presented only hex notation (*1), making it the de facto way to talk about binary.

While mini computers did take a slow change from octal to hex, basically all micros started out in Hex. Even CPUs like the 8080, with an instruction set clearly designed in octal, got published with all hex documentation. And as they say, the rest is history.

*1 - L'esprit de l'escalier: IBM did add decimal/octal conversion tables to some early manuals.

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    “ sucking in everyone able to spell at least two letters of COBOL” 🤣🤣
    – zarchasmpgmr
    Jun 7, 2020 at 1:16
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    A reason not mentioned is, that it is a noticable advantage (for base conversion routines) , to have consecutive character encodings for the additional "digits"; this eliminates all irregular examples from the question. IBMs EBCDIC encoding had lots of ugly gaps.
    – guidot
    Jun 17, 2020 at 14:58
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    @guidot ?? Neither EBCDIC nor ASCII has a consecutive order between digits and letters. Both have them in separate blocks. But more important, binary to readable-hex on a /360 was never done by calculation, it's a simple two instruction unpack and translate ( UNPK TEXT(9), WORD(5) + TR TEXT(8),ETOHEX-240 + ETOHEX DC "0123456789ABCDEF"). No calculation ever, so no need to be consecutive in any way.
    – Raffzahn
    Jun 18, 2020 at 13:16
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    @Raffzahn: Misunderstanding; Yes, one gap between digits and the first letter is practically not avoidable, but the following letters should be on subsequent positions., which fails for K, S, N, J
    – guidot
    Jun 18, 2020 at 13:44
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    @guidot Erm, yes, but having the letters consecutive isn't of any help. Code transformation should always be made as abstract as possible, no matter if using Assembly or any other language. Keep in mind, there are codes where neither letters nor numbers are in sequence. Above sniplet can be compiled with any character code (oops, should read ETOHEX-'0'). Similar in BASIC the core line would be TEXT$ = TEXT$+ MID$("0123456789ABCDEF",DIGIT,1) and so on. Avoid assuming a code set wherever possible. It's the compilers job to get around that.
    – Raffzahn
    Jun 18, 2020 at 14:03

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