PCI Express 1x - 98 pin Female Connector
The PCI Express (PCIe) x8 connector is a card-edge slot defined by the PCI Special Interest Group (PCI-SIG) in the PCI Express Card Electromechanical (CEM) Specification, with Revision 3.0 published in July 2013. It carries eight serial point-to-point differential lanes (each lane a transmit and a receive differential pair) replacing the shared parallel bus of conventional PCI, and provides +12 V and +3.3 V power rails alongside management signals such as SMBus, JTAG, and presence-detect lines. The connector uses a 1.0 mm contact pitch and totals 98 pins (49 per side A and B), supporting link speeds of 2.5 GT/s (Gen 1), 5.0 GT/s (Gen 2), and 8.0 GT/s (Gen 3) on the same physical slot. PCIe x8 slots are widely used in servers and workstations for network interface cards, storage controllers (HBAs), and GPU-compute cards, and are backward compatible — an x4 card inserted in an x8 slot negotiates to x4 speed.
| Pin | Side B Connector | Side A Connector |
|---|---|---|
| # | Name | Description |
| 1 | +12v | +12 volt power |
| 2 | +12v | +12 volt power |
| 3 | RSVD | Reserved |
| 4 | GND | Ground |
| 5 | SMCLK | SMBus clock |
| 6 | SMDAT | SMBus data |
| 7 | GND | Ground |
| 8 | +3.3v | +3.3 volt power |
| 9 | JTAG1 | +TRST# |
| 10 | 3.3Vaux | 3.3v volt power |
| 11 | WAKE# | Link Reactivation |
| 12 | RSVD | Reserved |
| 13 | GND | Ground |
| 14 | HSOp(0) | Transmitter Lane 0, Differential pair |
| 15 | HSOn(0) | GND |
| 16 | GND | Ground |
| 17 | PRSNT#2 | Hotplug detect |
| 18 | GND | Ground |
| 19 | HSOp(1) | Transmitter Lane 1, Differential pair |
| 20 | HSOn(1) | GND |
| 21 | GND | Ground |
| 22 | GND | Ground |
| 23 | HSOp(2) | Transmitter Lane 2, Differential pair |
| 24 | HSOn(2) | GND |
| 25 | GND | Ground |
| 26 | GND | Ground |
| 27 | HSOp(3) | Transmitter Lane 3, Differential pair |
| 28 | HSOn(0) | GND |
| 29 | GND | Ground |
| 30 | RSVD | Reserved |
| 31 | PRSNT#2 | Hot plug detect |
| 32 | GND | Ground |
| 33 | HSOp(4) | Transmitter Lane 4, Differential pair |
| 34 | HSOn(4) | GND |
| 35 | GND | Ground |
| 36 | GND | Ground |
| 37 | HSOp(5) | Transmitter Lane 5, Differential pair |
| 38 | HSOn(5) | GND |
| 39 | GND | Ground |
| 40 | GND | Ground |
| 41 | HSOp(6) | Transmitter Lane 6, Differential pair |
| 42 | HSOn(6) | GND |
| 43 | GND | Ground |
| 44 | GND | Ground |
| 45 | HSOp(7) | Transmitter Lane 7, Differential pair |
| 46 | HSOn(7) | GND |
| 47 | GND | Ground |
| 48 | PRSNT#2 | Hot plug detect |
| 49 | GND | Ground |
Notes
- The x8 slot is physically longer than x4 but shorter than x16; an open-ended x8 slot may accept x16 cards electrically limited to x8 speed.
- Contact pitch is 1.0 mm; sides A and B are on opposite faces of the card edge.
- The keying notch separates the power/management section (pins 1–11) from the high-speed lane section (pins 12–49 on each side).
- PRSNT1# and PRSNT2# are presence-detect signals used by the system to detect card insertion and enable hot-plug support.
- PERST# (not shown in this table) is the PCIe reset signal driven by the system to the add-in card.
- All TX and RX high-speed pairs must be AC-coupled per the PCIe Base Specification; coupling capacitors are placed on the add-in card.
- Gen 1 (2.5 GT/s), Gen 2 (5.0 GT/s), and Gen 3 (8.0 GT/s) use the same connector and are negotiated at link training time.
Signals
- +12V — primary power rail supplying the add-in card
- 3.3Vaux — auxiliary 3.3 V rail, always present even when main power is off; used to maintain wake logic
- +3.3V — secondary power rail
- GND — signal and power ground
- SMCLK — SMBus clock line for system-management communication
- SMDAT — SMBus data line for system-management communication
- WAKE# — active-low signal asserted by the card to request link reactivation from a low-power state
- JTAG1 (+TRST#) — JTAG Test Reset, part of the boundary-scan chain for board-level testing
- RSVD — reserved; must not be connected by the add-in card
- PRSNT#2 — presence-detect output from the card; pulled low to indicate card is seated; also used for hot-plug detection
- HSOp(n) / HSOn(n) — high-speed output (transmitter) differential pair for lane n; positive (+) and negative (−) signals of the serial lane