What Is an MXM Slot?

An MXM slot is where an MXM GPU module plugs into a computer. It is not a slot in the PCIe card sense, with a bracket and an opening in the case. It is a right-angle edge connector on the motherboard or a carrier board, a set of standoffs that hold the module flat, and a cooling interface that presses a heat spreader or cold plate onto the GPU and its memory.

The module carries the graphics processor and its memory, as our guide to what an MXM GPU is explains. The slot provides everything else: PCI Express lanes from the processor, power, control signals and a path for the display outputs to reach the connectors on the case. Because the module lies flat, the slot also decides how the GPU is cooled, which is why MXM suits sealed and fanless systems where a full-height graphics card would not fit or would not last.

MXM 3.0 and its 3.1 update use a 314-pin edge connector, the same on every module size. Through it the slot provides four groups of signals:

MXM 3.x defines two module sizes. Both are 82 mm wide and use the same connector. What changes is the depth of the module, and with it the room for a larger GPU, more memory and stronger power circuits. A third label, Type B+, is used by module makers for high-power modules on the Type B outline.

Because Type B+ is not a separate size in the specification, a B+ module needs a slot and thermal solution designed around it, not just any Type B slot. The power figures above are typical of current modules; each module’s datasheet sets its exact rating.

The datasheet is the reliable source. Look for four things: the MXM version, the type, the PCIe lane count and the maximum module power. If a datasheet says only “MXM 3.1 slot”, ask which type and what power the slot supports before choosing a module.

On the board itself, the standoffs show the size: they are set for a 70 mm module on a Type A carrier and a 105 mm module on a Type B carrier, and some Type B carriers have both positions. In our MXM GPU computers, some box PCs put the slot on a separate MXM layer, and the deeper version of that layer takes a Type B module in place of a Type A one.

In most embedded systems an MXM module has no cooler of its own. The slot’s cooling interface does that job, using a heat spreader that conducts heat into the chassis, a fan cooler or a high-airflow fan cooler. Module makers offer the same GPU with each option, and the MXM GPU modules we supply list fan coolers and heat spreaders for most builds, with operating ranges such as 0 °C to 55 °C that depend on the cooler and the system around it.

That is why a slot is rated for a power level, not just a size. A Type A slot designed for a 35 W headless module may not shed the heat of a 60 W module with display outputs, even though both fit. Check the system’s temperature rating with the module you plan to fit, and see our guide to thermal throttling for what happens when a GPU runs too hot.

A standard slot makes upgrades possible but not automatic. A newer module of the same type will plug in, but the carrier has to supply its power, the BIOS has to recognize it and the cooler has to match the new chip and memory layout, which can change between generations. Display outputs may also be wired differently.

In embedded systems the module is normally chosen when the system is specified and kept for the life of the design. Embedded MXM modules have long availability, which is one reason rugged GPU computers use them, and changing the module later is treated as a system change to check with the supplier.

We fit the MXM module, cooler and GPU drivers to suit the slot and the enclosure as standard, so the system arrives ready for its workload.