Back at the start of 2020, I wondered if common (x86 desktop) motherboards would ever have very many M.2 NVMe drive slots, where by 'very many' I meant four or so, which even back then was a common number of SATA ports for desktop motherboards to provide. At the time I thought the answer was probably no. As I recently discovered from investigating a related issue, I was wrong, and it's now fairly straightforward to find x86 desktop motherboards that have as many as four M.2 NVMe slots (although not all four may be able to run at x4 PCIe lanes, especially if you have things like a GPU).

For example, right now it's relatively easy to find a page full of AMD AM5-based motherboards that have four M.2 NVMe slots. Most of these seem to be based on the high end X series AMD chipsets (such as the X670 or the X870, but I found a few that were based on the B650 chipset. On the Intel side, should you still be interested in an Intel CPU in your desktop at this point, there's also a number of them based primarily on the Z790 chipset (and some the older Z690). There's even a B760 based motherboard with four M.2 NVMe slots (although two of them are only x1 lanes and PCIe 3.0), and an H770 based one that manages to (theoretically) support all four M.2 slots at x4 lanes.

One of the things that I think has happened on the way to this large supply of M.2 slots is that these desktop motherboards have dropped most of their PCIe slots. These days, you seem to commonly get three slots in total on the kind of motherboard that has four M.2 slots. There's always one x16 slot, often two, and sometimes three (although that's physical x16; don't count on getting all 16 PCIe lanes in every slot). It's not uncommon to see the third PCIe slot be physically x4, or a little x1 slot tucked away at the bottom of the motherboard. It also isn't necessarily the case that lower end desktops have more PCIe slots to go with their fewer M.2 slots; they too seem to have mostly gone with two or three PCIe slots, generally with limited number of lanes even if they're physically x16.

(I appreciate having physical x16 slots even if they're only PCIe x1, because that means you can use any card that doesn't require PCIe bifurcation and it should work, although slowly.)

As noted by commentators on my entry on PCIe bifurcation and its uses for NVMe drives, a certain amount of what we used to need PCIe slots for can now be provided through high speed USB-C and similar things. And of course there are only so many PCIe lanes to go around from the CPU and the chipset, so those USB-C ports and other high-speed motherboard devices consume a certain amount of them; the more onboard devices the motherboard has the fewer PCIe lanes there are left for PCIe slots, whether or not you have any use for those onboard devices and connectors.

(Having four M.2 NVMe slots is useful for me because I use my drives in mirrored pairs, so four M.2 slots means I can run my full old pair in parallel with a full new pair, either in a four way mirror or doing some form of migration from one mirrored pair to the other. Three slots is okay, since that lets me add a new drive to a mirrored pair for gradual migration to a new pair of drives.)