2.2.6 PCI (Peripheral Component Interconnect) - Notes
PCI is a legacy expansion bus that has been superseded by PCIe. It still matters because some older motherboards include PCI slots alongside PCIe slots for backward compatibility.
PCI Specs
| Specification | Value |
|---|---|
| Communication type | Parallel, unlike PCIe which is serial |
| Bit width | 32-bit |
| Speed | 33.3 MHz |
| Max transfer rate | 133 MBps |
Voltage and Keying
| Voltage | Notes |
|---|---|
| 5V | Original PCI cards |
| 3.3V | Became more common later |
| Dual-voltage | Supports both 5V and 3.3V |
Different keying, or notch positions, on cards and slots prevents incompatible voltage cards from being inserted incorrectly.
PCI vs PCIe Compatibility
- PCIe is software-compatible with PCI, so a PCIe motherboard can still include PCI slots to support legacy cards.
- PCI cards cannot fit into PCIe slots because they are physically incompatible.
- PCIe replaced PCI because serial communication and dedicated point-to-point links are faster and more efficient.