[ScottBurson]

On an ASR33 Teletype, backspace simply moved the carriage one character position to the left.

Rubout was a different concept entirely. The ASR33 had a paper tape punch and reader. The Rubout character was 0x7F, i.e., it had all bits set. So, to "rub out" an erroneous character from the paper tape, you could back the tape up in the punch to the desired character (by pressing a button on the punch; there was no character that invoked this function) and hit Rubout; this would punch the tape at all seven holes, changing whatever character had been there to a Rubout. (The software ignored Rubout characters on input.)

When the world moved on from Teletypes, it was natural for people to want a single keystroke that meant "delete the previous input character". But there was evidently some divergence of opinion in the industry as to whether that should be Backspace or Rubout -- notwithstanding that the ASR33's concept of Rubout didn't really map at all onto the new hardware.

[kps]

  > notwithstanding that the ASR33's concept of Rubout didn't
  > really map at all onto the new hardware.

If you are working with paper tape, Rubout (DEL in ASCII parlance), like every other code, advances the tape when punched. So, if the tape is a stream of characters, DEL erases the one under the cursor and leaves the cursor on the character formerly to the right. That is, Rubout/DEL is defined as a ‘forward delete’ operation, and that's something that remains useful.

That leaves Backspace as the natural choice for entering ‘backward delete’ on a keyboard, at least after 1979 when you have the ANSI X3.64 escape sequences for explicitly nondestructive cursor keys. I think there's a reasonable argument for Backspace being nondestructive for overstrike effects (accents, underlining, APL, etc.), especially when received by a terminal, but I know none for changing the meaning of DEL.

[flukus]

> On an ASR33 Teletype, backspace simply moved the carriage one character position to the left.

Exactly what a typewriter would do because it couldn't erase the ink on the paper.