US What Mini PCIe is
Mini PCIe, short for PCI Express Mini Card and often written mPCIe, is a small card that plugs flat onto a motherboard to add a function without a cable or a full-size slot. PCI-SIG defined it in 2003 to replace Mini PCI in laptops, mainly so Wi-Fi and modem cards could change without redesigning the board.
The card has a 52-pin gold edge connector at one end. It slides into the socket at an angle, is pushed flat and is held by two screws or a latch, which keeps it in place under shock and vibration. The socket carries several interfaces at once: a single PCI Express lane, a USB 2.0 port, SMBus for management, a SIM (UIM) interface for cellular cards, LED outputs and a wireless disable line.
That mix is the key to understanding Mini PCIe. A card can use the PCIe lane, the USB lines or both, and the host board decides which of them are actually wired to each socket.
Full-size vs half-size Mini PCIe cards
The standard defines two lengths, both 30 mm wide. A full-size card is 50.95 mm long and is held by two screws at the far end. A half-size card is 26.8 mm long and is also fixed at its far end, so it needs a standoff at the half-length position. Boards provide either a full-length socket, a half-length socket or a full-length socket with a second standoff at the half position, so check which a board has before ordering a card. A bracket extender lets a half-size card sit in a full-length position.
Which bus a Mini PCIe card uses
Two cards can fit the same socket and still not work, because one needs PCIe and the other needs USB. This is the most common Mini PCIe problem in the field, and datasheets don’t always say it clearly.
| Card type | Bus used | Needs SIM socket | Notes |
|---|---|---|---|
| Wi-Fi and Bluetooth | PCIe for Wi-Fi, USB for Bluetooth | No | Bluetooth fails if the socket has no USB |
| 4G LTE modem | USB | Yes | Most cellular modules are USB-only |
| GNSS receiver | USB | No | Often with dead reckoning for vehicles |
| Serial, CAN and digital I/O | PCIe | No | Industrial expansion on compact boards |
| Gigabit Ethernet | PCIe | No | Adds a LAN port through a cable |
| Video capture | PCIe | No | HDMI, SDI or analog inputs |
| mSATA SSD | SATA, not PCIe | No | Same card shape, different signals |
PCIe on Mini PCIe is a single lane, typically Gen 1 or Gen 2 depending on the host, giving around 250 or 500 MB/s each way. That is ample for wireless, serial and 1080p capture. Workloads that need more bandwidth move to M.2, which carries up to four lanes. Our explainer on how M.2 keying decides what fits a slot covers the newer format.
Why Mini PCIe suits industrial computers
M.2 has replaced Mini PCIe on most new laptops, but the older format remains common on industrial boards, gateways and rugged systems, where its size and long product life suit fielded equipment.
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Screwed down, not slotted. The card lies flat and is fixed at both ends or the centre, so it copes with vibration on vehicles and machines.
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Cellular with a SIM on board. The socket’s SIM interface lets a 4G modem and its SIM sit inside the enclosure, as covered in our guide to integrating 4G, LTE and 5G connectivity.
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Focused I/O cards. Serial, CAN, digital I/O and Ethernet cards add exactly the ports a project needs without a PCIe slot or a stacked expansion board.
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Video capture in compact systems. Mini PCIe capture cards add HDMI, SDI or analog camera inputs to small embedded computers.
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Long-lived designs. Many boards and cards stay in production for years, so a socket specified today can still be populated for replacements later.
Where to find Mini PCIe sockets
Mini PCIe sockets are most common on compact boards and systems built for expansion inside a small enclosure. Many of our 3.5-inch SBCs have one or two Mini PCIe sockets, often with a SIM holder beside one of them. Our industrial IoT gateways typically use a Mini PCIe socket for the cellular modem, and several NVIDIA Jetson box PCs keep one alongside their M.2 slots for Wi-Fi or LTE.
Before choosing a card, check four things on the board’s manual: the socket length, whether PCIe, USB or both are wired, whether there is a SIM holder, and whether the socket can also take mSATA.
Quick answers on Mini PCIe
Mini PCIe: common questions
How many pins does a Mini PCIe card have?
52. The edge connector has 52 contacts across both sides of the card, the same count as mSATA, which is why the two share a socket.
Is Mini PCIe the same as Mini PCI?
No. Mini PCI is the older, larger card that carried the parallel PCI bus on a 124-pin connector. Mini PCIe replaced it and the two are not compatible.
Can a Mini PCIe card go in a full-size PCIe slot?
Yes, with an adapter. A passive carrier board puts the Mini PCIe card on a standard PCIe ×1 bracket. Cards that need USB or a SIM need an adapter that provides them.
What is a half-size Mini PCIe card?
A shorter card for the same socket. It is 26.8 mm long instead of 50.95 mm. It needs a socket with a standoff at the half-length position, or a bracket extender to reach a full-length one.
Can I put an mSATA SSD in a Mini PCIe slot?
Only if the socket supports it. Some boards detect mSATA and switch the socket to SATA. On a PCIe-only socket the drive will not be seen.
We fit Mini PCIe and M.2 cards as standard in the systems we build, matching each card to a socket wired for its bus, installing the SIM, antennas and drivers, and checking every card works before the system ships. Tell us the wireless, I/O or capture you need, and we will specify the cards and the board to carry them.