I was thinking of 386 era computers and strictly speaking it was just parity RAM, not ECC. Which often led to annoyances when a single parity error would cause your whole computer to halt.

Wikipedia says "By the mid-1990s, most DRAM had dropped parity checking as manufacturers felt confident that it was no longer necessary.". https://en.wikipedia.org/wiki/RAM_parity

I'd love to read a technical deep dive on RAM reliability over time. You'd think with increasing memory cell density and overall larger RAM the number of absolute errors on a desktop computer would be going up over time.

I can remember 486 Motherboard in Packard Bell (quite the entry brand...) systems frequently used 36 bits ECC FP SIMMs.

Printers and plotters from this era used ECC modules most of the time.

But by the end of the century, they were replaced by unbuffered, unregistered 16/32/64 bits modules.

Every mid range server still use ECC. Entry HPE Servers use ECC UREG (unregistered, 9 chips) modules, while mid range and more use ECC REG modules (9 chip + interface controller onboard). Ironically, UREG module are more expensive than ECC REG.

Also, most workstations used ECC modules. Less frequently since 4-5 years.

I know the Pentium Pro/2/3 chipsets and motherboards all(?) supported it. Unsure of the Pentium 1 as the 430TX on my Tyan Tomcat IV doesn't, and that is a dual processor board. 486 and earlier likely depended on the chipset as there were many.

At work I have two working slot 1 PIII 800's each with 1GB ECC (4x 256MB DIMMS) on a regular Asus board (doing nothing but waiting to go home with me one day). The board reports the RAM is in fact ECC and that it is enabled.