I/O Interfaces & Buses

What does it mean that a PCI Express lane is full duplex?

  1. AIt can transmit and receive simultaneously
  2. BIt alternates between transmitting and receiving
  3. CIt can only transmit, never receive
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Answer: A. It can transmit and receive simultaneously

Full duplex means data can flow in both directions at once. A PCI Express lane has separate transmit and receive differential pairs, so it can, for example, send data to a GPU while simultaneously receiving results back. This is why bandwidth figures must state whether they are per direction or a two-way total. Using one set of wires alternately is called half duplex.

  • A. Correct. Transmit and receive use separate differential pairs.
  • B. That is half duplex.
  • C. It can receive too.
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More I/O Interfaces & Buses questions

  1. Which describes the credit-based flow control used in PCI Express?
  2. In AI systems with many GPUs, why are dedicated high-speed GPU-to-GPU links (such as NVIDIA NVLink) used in addition to PCI Express?
  3. In PCI Express, sending many packets that each write 64 bytes yields effective bandwidth well below the theoretical figure. What is the main reason?
  4. Which statement is correct about DMA using a ring of descriptors in memory, as widely used by network cards and NVMe SSDs?
  5. Which statement is correct about PCI Express link power saving (the L0s and L1 states of ASPM)?