I would expect that old DDR4 machinery to end up somewhere else, still chugging along. Maybe someone buys the old production and keeps chugging low quality DDR4 or something.
To me, it sounds like that didn't happened. Fabs that were producing legacy DDR4 are still producing it, just selling it higher and surfing on the consumer price increase of DDR5. As DDR5 became more expensive, people looked to build old AM4 PCs with the older memory, and the market just raised the price so that option would also cost more. IMHO DDR4 price increase has nothing to do with production.
There shouldn't be much issue converting those 16nm DDR4 fabs to DDR5, it's really just an issue of swapping out the masks. That's assuming they haven't all already been converted years ago.
Even when there isn't an overlap, moving to the next process node usually isn't so much about replacing machines, but adding more machines. To oversimplify, you might not be able to convert one older DDR4 fab to DDR5, but sometimes you might be able to convert two older DDR4 fabs to one DDR5 fab.
Such conversions might not be the most cost-effective option in the long run (that unmodified fab could have kept selling DDR4 for years), but conversions might be significantly faster than building new fabs.
Like everything related to it being a clean room; All the logistics robots which move wafers around; All the machines that deposit layers of material like CVD/AVD/Sputtering; The various machines that do the actual etching; The furnaces; The inspection and quality control equipment;
Also, absolutely everything to do with dicing and packaging. But that's usually already at another factory (often a completely different company) due to how process agnostic it is. Same applies to growing and prepping the silicon wafer.
The inspection and quality control equipment is one of those that you can't just reuse without careful transitioning. DDR5 has much higher speeds, on-die ECC and all sorts of complications DDR4 doesn't have.
At least with logic ICs, they either testing/QC/bining as part of packaging (before dicing), or even have factories that specialise in just testing/QC/Binning. Such fallacies need to be flexible enough to deal with thousands of different IC designs, and there is no reason to tie them to a given process node.
I guess with memory, there are only three-ish designs (DDR, LPDDR, HBM), so maybe it does make sense to integrate testing/QC/binning into the fab.
But I doubt they would have any trouble switching it out.
packaging before dicing? That makes no sense.
I built a new gaming PC with DDR4 two months ago and it's pretty great. For servers RAM speed usually matters even less.
I'm posting this from a machine that uses DDR3 and is still perfectly capable of meeting my needs.
DDR5 fabrication requires a sub 15mm process, much more complex mounting and lots more testing equipment. It means you can't just quickly convert a DDR4 fab to DDR5.
It was meant to explain that DDR4 price increase has nothing to do with supply chain lanes, and it's more of an artificial demand manipulation than anything else.
There's no evidence of anything artificial here, except to the extent that the data center-driven demand could be called "artificial". When prices for DDR5 go up, it's only to be expected that this induces demand for DDR4, the spillover from people who were priced out of DDR5. Much the same principle that rent control advocates stumble on: "affordable housing" is mainly a consequence of more housing, rather than something to target directly.
I'm sorry. Can you summarize that part in a more concise phrase?