I have an old (no more than 5 or 6 years) Compaq that I'm planning to re-purpose. The motherboard and CPU need to be replaced but I'm going to be able to re-use the hard drive and optical drives. I'd also like to be able to re-use the case. I'd heard that some Compaq (as well as Dell, HP, etc…) build motherboards with non-standard form-factors that only they (the vender) use. How would I be able to determine if the case can take a standard form-factor or if it only takes a special Compaq form-factor? The case itself is a standard, mid-tower size.
How to determine motherboard/case form factor
caseform-factormotherboard
Best Answer
In all likelihood, if the system uses a proprietary form-factor, it probably won't be the actual physical dimensions (width, length) that are the problem but rather the placement of components on the backplane and of the standoff holes.
If the backplane is unusual, you can probably/hopefully just pop in a compatible bezel (figure 1), though the case may not be designed to support replacing the bezel (you may be able to just cut a hole).
If the standoff holes (figure 2) are in the wrong place, then you may have to find other means of securing the board to the case, or if you are lucky, perhaps secure it with just one or two screws.
FormFactors.org has a comprehensive list of form-factors for motherboards, power-supplies, and other components, with links to PDFs of the specifications for each that include dimensions and mounting-hole placements.
Figure 1: Variety of bezels:
Figure 2: Standoff holes: