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

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.