[jacobush]

Also used in early revisions of the Amiga. (BCPL or Amiga Basic used pointer tags for something like garbage collect or frame pointers or something IIRC.) Mac had something called 32 bit clean which I imagined could have been pointer tagging.)

[krallja]

"32 bit clean" meant that the ROM didn't use pointer tagging; otherwise it was using the top 8 bits for its own purposes and wouldn't run on machines which used the full 32-bit address line.

http://lowendmac.com/2015/32-bit-addressing-on-older-macs/