History of ASCII – Why Was It Needed?

The concept of character sets is older than Unicode.

Before Unicode, a character set defined a set of characters and how each character was represented as bits. Most character sets mapped a character to a byte (which allowed a set of 256 characters), some mapped to two bytes, and a few (like ASCII) to only 7 bits. Different character sets often assigned different values to the same character, and there was no universal translation key between the various character sets in use.

Unicode was an attempt to solve this problem by unifying all the various character sets in a common "superset". For this purpose Unicode introduced some additional levels of abstraction, for example the concept of character encodings as something separate from the code point values. This allowed Unicode to redefine the pre-unicode character sets as unicode character encodings.

The charset attribute in HTML (which mirrors the charset parameter in the HTTP content-type header) for example, is from before unicode was widely adopted, but when it was decided to accept unicode as the universal character set of the internet, the charset attribute was just redefined to specify the encoding in use, but the name wasn't changed to allows backwards compatibility.

Time-sharing, multi-user, systems were invented in the late fifties, but they were comparatively rare through all through the 60s. Most computers ran in batch mode, running a single program at a time, with no facilities for interacting with users other than the card reader, the line printer, and maybe a separate teletype for the console operator. Terminals you say? Up until the late 60s, electronic terminals with video displays were exotic, fabulously expensive gadgets limited to research facilities and specialized jobs like air traffic control, and national defense. Those computers that did support interactive sessions generally used teletypes. Entering a program on a teletype was just as unpleasant as punching it onto cards.

Let me expand a little bit on the problem of batch processing since it is so foreign to the way most people use computers now. It would certainly have been possible even in the 50's to write an interactive editing program that would have worked with a teletype. However, because of batch processing, the editing program would have completely monopolized the computer the entire time you were sitting at the teletype editing your program. Since several hundred to several thousand other people would have been waiting their turn to run their programs, you would have been a very unpopular person. You would also have been charged several dollars a minutes while your editor was running. It was much more cost-effective to write your program out in long hand, hand the final draft to a key punch operator, and let them transcribe your program onto punch cards or paper tape. That avoided wasting the CPU's precious milliseconds waiting for you to type 'GOSUB'.

Hard disk drives were also invented in the late fifties, but they were small (around 1mb), rare and expensive, not something you gave users casual access to. Obviously users did need some sort of long term storage. The choices were paper tape, punch cards and magnetic tape. Magnetic tape was new and expensive. Paper tape was used by some systems, but punch cards were an established technology used in non-computer business machines like tabulators and sorters since 1928, so a lot of businesses already had a major investment in punch card machinery and storage.