Etienne Lorrain (etienne_lorrain.delete@this.yahoo.fr) on March 4, 2021 6:26 am wrote:
>
> Historically, I think ECC error detection was removed approximately at the time it took too much time to
> initialise the memory. At power-up, the parity bit is not initialised: if you dump the DDR before initialisation
> you get mostly zero bits but you will also get bits set (I do not know why the capacitor is still charged
> at power-up). If you do a quick power-cycle, it is obvious you will still have bits set.
> When the memory of the PC increased to few tens of megabytes, the CPU (at that time) was
> not able to clear that DRAM (so initialise the ECC) in less than 10 seconds, and the PC never
> had a powerful DMA to do such work. To cut boot time, they removed the parity bit.

Or you could not bother clearing memory. BIOS/Bootloaders need to initialize however much they use, the kernel needs to keep a bit per page to indicate whether memory has been cleared before and lazily do the work as memory gets allocated. We did that in a past project. It has the added benefit that you can leave crash dumps in RAM and retrieve them after reboot.