Very cool. Seeing how almost everything from WiFi, to NVME SSDs, (to apparently USB ports sometimes?) are connected to it, is PCIe the only high-speed interconnect we have for peripherals to communicate with modern CPUs?

The high speed signals that come out of mainstream CPU chips are generally DDR, SMP, and PCIe. Outside of a very few exotic things that use QPI or HT to connect, or exotic storage might use DDR, yes high speed off-chip peripherals use PCIe.

NVLink is another one you might have heard of, although it might also fall in the exotic category. I think some systems take AXI off-chip too. So there's various other weird and wonderful things. But none you're likely to have in your PC I think.

On-chip is another story, you can connect USB or NVMe or GPU "peripherals" using an on-chip interconnect type. But I guess you are asking about off-chip.

> PCIe the only high-speed interconnect we have for peripherals to communicate with modern CPUs?

In a pedantic/technical sense, no. Practically speaking though, yes.