Mac mini 1.42 resolution problem

Hmmm... that's odd although it does make sense in a way. 1280x800 is exactly half the resolution of the 30" ACD (I'm guessing its an Apple Cinema Display) and so each pixel is being enlarged to take up four. That way there's no funny scaling going on and there aren't any blurring effects or pixel anomalies.
Running 1280x800 on a 30" ACD looks better than running 1920x1200 on it.

 

The tech specs of the 30" display says it supports
2560 x 1600 pixels (optimum resolution)
2048 x 1280
1920 x 1200
1280 x 800
1024 x 640
so it's a bit strange that you don't get that option.
Edit: By "that option" I mean 1920x1200.

 

The Mac mini can't possibly support a 30" display... can it? It'd need dual-link DVI would it not?

 

Not at full resolution, no, but apparently at least 1280x800 using single-link DVI.

 

You may try dropping down to thousands of colors to see if that frees up enough VRAM to allow the higher resolution. I don't know if you'd want to run it like that, but if it works you'll at least know where the missing resolution option went.

 

'displayconfigx' allows you to configure custom resolutions - you can find it on versiontracker.

 

It has nothing to do with VRAM. It has to do with bandwidth. The DVI interface specifies that no matter what color depth you are at, it sends 32-bits of data per pixel. And the 30" display requires more bandwidth than DVI is capable of. Hence the need for a 'dual-link DVI' connection. (Two DVI connections in one connector.) This actually gives enough bandwidth for 3840x2400, more than enough for a 30" display.

So, in short, unless your hardware has a dual-link DVI port, there is *NO* way you will get a 30" display to run at its full resolution. The mini has a maximum resolution of 1920x1200. Period. To quote Apple's mini What's Inside page:

 

Learn to read. You missed that the original poster was not trying to get the full resolution of the 30" display, but the maximum resolution that the mini is supposed to support (1920x1200).