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26

There is a clue in the name - BCD stands for "binary-coded decimal", where 4 bits are used to represent 1 decimal digit (0-9). The hexadecimal values A-F are not used in BCD. EBCDIC is an extended version of BCDIC, and it shifts BCDIC alphanumerics, and inserts characters in some of the non-decimal positions. But there's a simple relationship to ease ...


20

As pointed out by Jon Custer, part of the reason is due to the input at the time being punch cards. If holes were close together there was a risk of the card being unreadable or ripping. In addition, this punch card from the Wikipedia article helps explain why both uppercase and lowercase end at 0x_9. The punch card only goes from 0 to 9. I don't know how A ...


19

TL;DR: ASCII was never intended for processing, just as an interface standard for data exchange (hence the name American Standard Code for Information Interchange) IBM never switched, it still uses EBCDIC within mainframes and ASCII for communication. IBM was a major proponent for ASCII, but not the sole force, and especially not international. ASCII soared ...


19

IBM started using ASCII before 1970; the 2260 terminal, released in 1964, used the unpublished (but ratified) 1965 version of the ASA X3.4 standard. IBM mainframes still use EBCDIC, so I don’t think their popularity had much bearing on the popularity of ASCII (but other encodings’ popularity influenced IBM mainframes: their instruction set includes ...


4

The document everything seems to refer back to is IBM's "Character Data Representation Architecture Reference and Registry" (SC09-2190-00). There is a copy here, in IBM's BookManager format: https://www-01.ibm.com/servers/resourcelink/svc00100.nsf/pages/zosv1r13-pdf-download?OpenDocument (search for SC09-2190, about three-quarters of the way down a long web ...


4

In the 1960s, IBM used a crazy variety of character codes. IBM was the king of punched cards, commonly known as "IBM cards", so many codes related to the sparse 12 bit codes used for those. However, even these were not fully standardized: different keypunch models used different character sets! 6-bit BCDIC was designed to easily map to the most ...


2

Answering one of your questions "When did ASCII become a worldwide standard", the answer is: never. The "A" stands for "American". At the time the US adopted ASCII, other countries were adopting their own variants, substituting different characters according to national needs: for example in the UK, "£" was substituted ...


2

I'm going to provide a terrible answer, but include a couple references that might be great for nostalgia. One is NostalgiaNerd on youtube, he provides a British viewpoint of IBM's shift to ASCII (OK they only did it through codepages, not really fully/completely ASCII). The video is strangely titled, nothing about ASCII or EBCDIC in the name: "These ...


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