It was about saving memory by tokenizing keywords: '?' is how PRINT actually was stored in program memory, it just rendered as 'PRINT'. Most other tokens were typically the first two characters, the first lowercase, the second uppercase: I remember LOAD was 'lO' and DATA was 'dA', though on the C64's default character glyphs they usually looked like L<box char HN won't render> and D<spade suit char>.

All this being on a C64 of course, but I suspect most versions of Bill Gates's BASIC did something similar.

C64 basic was tokenized into one byte, with the most significant bit set: https://www.c64-wiki.com/wiki/BASIC_token

Each command could be typed in two ways: the full name, or the first two letters, with the second capitalized. Plus a few exceptions like "?" turning into the PRINT token ($99, nowhere near the PETSCII value for ?) and π becoming $FF.

The tokens were expanded into full text strings when you would LIST the program. Which was always amusing if you had a very dense multi-statement line that expanded as longer than the 80 characters the c64's tokenizer routine could handle, you'd have to go back and replace some or all commands with the short form before you could edit it.

the zx spectrum did this too, except you could only type the "short forms" (which were always rendered in full). It had keywords on its keys. I.e. to type print, you had to press the "print" key.

You could run them just fine as long as you didn't try to edit the listed lines if they were longer than two screen lines. The same is true for a C128 in C128 mode, except the limit is extended to 160 characters (four 40-column lines).

D♠