SSD – Connect PCIe 3.0 SSD to Another Computer

USB is slower then SATA. The new SATA 3 standard operates at a theoretical maximum rate of 6.0 Gbps, while USB 3 operates at a theoretical maximum of 4.8 Gbps bi-directional. If we crunch these numbers...

      USB 3.0                    SATA 3
      4800Mbps            6000Mbps each way
      600 MBps            750 MBps each way

      USB 2.0                    SATA 2
480Mbps divided by 2      3000Mbps each way
  240Mbps or 30MBps       375 MBps each way

EDIT: As per @MrAlpha, I stand corrected on USB 3; it can take advantage of Full Duplex (as described here)

All PCIe SSDs support any number of PCIe lanes. Both devices and slots are intercompatible providing you can find a card that will fit. Most native PCIe SSDs are fairly expensive and require a larger slot, so you will need an open-ended x1 slot.

M.2 SSDs don't fit into PCIe directly but you can get cheap, passive adapters like this one, though obviously you would need to look for one that is x1 if you do not have an open-ended slot.

Whether PCIe x1 is faster than SATA (there is no such thing as a "DATA connection") depends on what version of PCIe you have and what version of SATA you have. The following is a brief summary of speeds:

• PCIe v1 1x = 2.5Gbps raw = ~250MB/sec
• PCIe v2 1x = 5.0Gbps raw = ~500MB/sec

• PCIe v3 1x = 8.0Gbps raw = ~1000MB/sec

• SATA 1 = 1.5Gbps raw = 150MB/sec

• SATA 2 = 3.0Gbps raw = 300MB/sec
• SATA "3" = 6Gbps raw = 600MB/sec

So if you have 6Gbps SATA and a PCIe v2 slot then no, it will not be faster (of note, all southbridge PCIe slots on Intel boards before Skylake are PCIe 2.0 only)

Your most important concern though should be whether your BIOS/EFI can boot from a PCIe SSD. Most older boards (>1 generation or >= 2 years) cannot boot from a native PCIe SSD so you must have a SATA SSD or HDD to boot from.