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The on-die ECC used by DDR5 (and pretty much all other recent DRAM) actually doesn't have many compatibility implications, precisely because it's done entirely on-die unlike traditional ECC memory modules that include an extra one or two chips to enable end to end ECC managed by the CPU's memory controller.

The more significant incompatibilities between DDR4 and DDR5 are in the power delivery (DDR5 has voltage regulators on the module rather than on the motherboard) and rearranging of the address bus and command encoding.

Oh, right, yeah I see the meta-confusion. They are incompatible for a bunch of reasons, of which ECC is not particularly relevant.

The incompatibility between DDR4 and DDR5 DIMMS is also enforced by a physically different notch and slot. It's always been this way.

Sure, but it's only obvious once you know that. Given that the N100 itself supports both DDR4 and DDR5, I think the confusion is entirely understandable.

DDR 4 and 5 are incompatible just because of the ecc?

You could desolder the ecc chip off a ddr 5 stick and then just plug it into a ddr 4 slot?

The reason why the author thought these might be interchangeable in the first place?