1. Backward Compatibility
    • Same connector → PCI-X cards can go in PCI slots (and vice-versa).
    • Same software model → OS, drivers, and applications work unchanged.
  1. Techniques for Higher Speeds
    • PLL (Phase-Locked Loop) Clocking
      • Generates phase-shifted clocks internally.
      • Outputs can be launched earlier, inputs sampled later → extends timing margin.
    • Registered Inputs
      • Signals are latched at the device pin.
      • Reduces setup time at the receiver (< 1 ns vs 3 ns in PCI).
    • Combined effect → more time for signal propagation, enabling higher bus frequency.
  1. Performance
    • PCI limited to 66 MHz, 533 MB/s (max 64-bit wide).
    • PCI-X raised frequency to 100–133 MHz, supporting much higher throughput.
  1. Limitations Still Present
    • Same reflected-wave bus model → bus loading still a bottleneck.
    • Could only support a few devices per bus.
    • To add more devices → required extra PCI-X bridges, increasing cost and board space.
    • Result = still an expensive and complex solution despite higher bandwidth.