The original IBM PC/XT had parity RAM. In the early PC/XT and PC/AT clones you had banks of 9 DIP sockets for memory chips with the 9th being for parity.

The DDR4 ECC RAM has 72 bits total and 64bits of data which means the same 9/8 ratio of data storage to usable data as the original PC/XT.

The Z80 and 6502 based computers in the 80s typically didn't have parity RAM. The Amiga and Macintosh were higher performance systems in the 80s which also didn't have parity RAM.

We could and should have gone straight from parity RAM to ECC RAM for everything.