> you just have 9 bits per byte rather than 8 bits per byte physically on the module. More chips but not different chips.

For those who aren't well versed in the construction of memory modules: take a look at your DDR4 memory module, you'll see 8 identical chips per side if it's a non-ECC module, and 9 identical chips per side if it's an ECC module. That's because, for every byte, each bit is stored in a separate chip; the address and command buses are connected in parallel to all of them, while each chip gets a separate data line on the memory bus. For non-ECC memory modules, the data line which would be used for the parity/ECC bit is simply not connected, while on ECC memory modules, it's connected to the 9th chip.

(For DDR5, things are a bit different, since each memory module is split in two halves, with each half having 4 or 5 chips per side, but the principle is the same.)