These names were very well thought out. They were part of a larger vocabulary in fact; most of that vocabulary died out and only car and cdr remained. There were things like cwr, ctr and others. MacCarthy and gang were well aware (of all people!) that the language is machine-independent and not something that will be forever stuck to the particular IBM machine; they used these names anyway because there was nothing wrong with them.
By the way, the C and R are not machine specific; any machine can have a "register" and any register can have "contents". On any machine where we implement cons cells, we can just call the two fields registers, understood as being A and D.
These, in turn, can be "ante" and "de", if someone desperately needs mnemonics:
In addition to car and cdr, there were cpr (Contents of the Prefix part of Register) and ctr (Contents of the Tag part of Register).
> By the way, the C and R are not machine specific; any machine can have a "register"
Slight nitpick: the first machine on which I had a decent Lisp to use (Portable Standard Lisp) was a Burroughs 6800, a stack machine with no general purpose registers, or indeed any registers directly accessible by the programmer.
Vi has "registers" and so do TeX and troff. I think once upon a time, it was more common to use the word for things beside CPU registers and I/O ports.
If a cons cell is a context with two registers (R) whose contents we can access (C), the only vestiges of that IBM machine are the A and D letters sandwiched in between to distinguish them.
Compared to how option letters change meaning between Unix commands, it's nothing. -h help? Nope, h)uman readable sizes.
^ to anchor regex at beginning; $ for end. Because on common keyboards, ^ is on the right, and $ on the left!
By the way, the C and R are not machine specific; any machine can have a "register" and any register can have "contents". On any machine where we implement cons cells, we can just call the two fields registers, understood as being A and D.
These, in turn, can be "ante" and "de", if someone desperately needs mnemonics:
https://en.wiktionary.org/wiki/ante
https://www.etymonline.com/word/de-
"active word-forming element in English and in many words inherited from French and Latin, from Latin de "down, down from, from, off; concerning."