• What it is:
  • If a PCI device can act as a Bus Master, it can transfer data directly to another PCI device.
  • This means the transaction happens entirely on the PCI bus, without involving system memory or the CPU.
  • Since both devices are equals (“peers”), this is called a peer-to-peer transaction.

Advantages

• Efficiency:
  • The transfer stays local to the PCI bus.
  • CPU, memory, and other system resources remain free to do other tasks.

Why it’s rarely used

• Compatibility issues:

  • Different devices often use different data formats.
  • Unless both devices are from the same vendor (and designed to work together), their data may not match.

• Workaround:

  • In most cases, data is still sent through system memory, where the CPU can reformat it before sending it to the target device.
  • This defeats the efficiency gains of direct peer-to-peer transfer.