I/O Interfaces & Buses

What happens when an x4 PCI Express SSD is plugged into a full-length x16 slot on a motherboard (assuming the slot is wired for at least x4)?

  1. AIt does not fit, so it cannot be inserted
  2. BIt works fine and connects with four lanes
  3. CIt automatically expands to 16 lanes, quadrupling bandwidth
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Answer: B. It works fine and connects with four lanes

In PCI Express, at the start of a connection both sides determine the lane counts and speeds they can use (link training) and operate at the largest common configuration. An x4 card in an x16 slot runs with four lanes. Conversely, a long slot may be wired for only x4, in which case an x16 card also runs at x4. Generations work the same way, settling on the speed of the generation both support.

  • A. A shorter card fits in a longer slot.
  • B. Correct. It runs at the lane count both sides support.
  • C. It cannot exceed the card's own lane count.
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More I/O Interfaces & Buses questions

  1. Which statement about the structure of PCI Express is correct?
  2. How does communication in PCI Express work?
  3. What does the PCI Express data link layer do about bit errors during transmission?
  4. How are the registers and memory of a PCI Express device made accessible to the CPU?
  5. What is a characteristic of MSI (message-signaled interrupts) used in PCI Express?