MXM Compatibility

Three compatibility types

Three different types of compatibility can be distinguished. Firstly, there is obviously the mechanical leg. Closely related is the thermal leg, and finally there's the software part. Information is very hard to get by, but what we have, you get!

However, please keep in mind that as long as manufacturers do not explicitly advertise that their laptop GPU's are MXM parts, they are in no way obliged to adhere to the rules Nvidia has drafted in their specifications. Furthermore, even if MXM is explicitly mentioned, there is no way to enforce full compatibility. In short, we once again stress the information contained in this page is for your viewing pleasure but does not guarantee anything.

Update (24 august 2007): Guess what: even if manufacturers advertise their notebook as MXM, that still doesn't give any guarantee it will work with other MXM hardware!

Mechanical and thermal

MXM System Type	Module Compatibility	Maximum GPU Size	Thermal Compatibility
I	I	35mm x 35mm	I
II	I,II	35mm x 35mm	II
III	I,II III	35mm x 35mm 40mm x 40mm	II III
IV	?	?	?
HE	I,II, III,HE	35mm x 35mm 40mm x 40mm	II HE

This is the table as it is provided by Nvidia. The 'Module Compatibility' is fairly straight forward: all modules of a 'lower' type can be mounted on a given MXM type motherboard. Practically, this means that the mounting holes that fit on the standoffs on the motherboard are always on the same spot.

The 'Thermal Compatibility' column seems less straightforward. First off all, this could mean a number of things. Is this about thermal capacity? Or rather about the mounting of the thermal solution. MXM Upgrade believes this it's the last .Unfortunately, , the table as it is provided by Nvidia seems not to match the mechanical dimensions they provide in the mechanical specifications document that can be found on this page. Apart from memory thermal pads that may require an increase in size, which is a rather minor issue, the determining factor to know whether the thermal solution will fit would seem to be the positioning of the mounting holes provided for the heatsink.

There are always four of these holes positioned around the GPU, but for Type I and II the upper left hole is positioned at 55,3mm from the bottom left corner, while Type III and HE feature the same hole at 60,5mm. We assume there are two possible explanations. One would be that there are more mechanical types than there are listed in the Nvidia document, namely a subtype of both Type III and HE. This 'subtype' would feature the overall dimensions of the 'mothertype', but it would provide the same mounting holes of Type II and it would feature the same GPU size.

Another possibility would be that the Nvidia made a mistake. Type I thermal solutions can be only mounted on Type II cards, and Type III is only compatible with Type HE. Keep in mind that this only takes the mounting holes into account. There' s still component height, thermal keep outs to consider after that.

We believe that there the first explanation is the right one. The overall Type III dimensions will have thermal provisions for either a Type /III thermal interface or for a Type III thermal interface.

That means that before you ever order an upgrade card Type III for your laptop, you must check your thermal interface's mounting provisions!

Update (24 august 2007): We included Type IV for good measure, but we have no idea about compatibility.

Software

Video Bios

The Video Bios is in the only place it can be, namely in a ROM on the MXM card itself. Indeed, as the MXM card can be removed/upgraded, this is the only way to ensure a matching Video Bios is loaded in the system. The Video Bios is a function of the actual card, and therefore it is logical that it is a part of it.

MXM information

All relevant information regarding the laptop must be communicated to the MXM. This information includes

Notebook output configuration.
Video out configuration.
MXM heatsink thermal rating.
Notebook power supply capabilities.

The output configuration is used to 'tell' the MXM what kind of panel is attached, if a DVI out is present, if there's TV out, what type it is etc.

The heatsink rating tells the MXM how much power the heatsink can evacuate, the power supply capability parameters tell the MXM how much electrical power the notebook can supply. The MXM may throttle it's speed if these numbers are not sufficient. We have no information whether notebook manufactureres actually use this information. This could be a source of incompatibility.

At least some of the Thermal Throttling for the MXM is currently only supported through Windows.

The above described information can be store in two places: either on a separate ROM on the motherboard, directly connected to the MXM, or as a space in the systembios. The latter offers easier tweaking, you might try the bios of a comparable laptop, but it is also the more dangerous option.

Last updated 24 august 2007