Coherence with 3 Displays

I have 3 displays connected to my Mac Pro. Two of them are at 1600x1200, and the third one is at 1280x1024. Coherence mode doesn't work for me. When I try to switch it gives the following error:

Unable to switch to Coherence Mode. primary operating system does not support screen resolution requested by guest operating system. Select another resolution for the guest operating system or review your video system configuration.

Any ideas?

Thanks!
jeremy

 

All displays need to use the same resolution for coherence to work when you have the "Use Multiple Displays" option enabled fromt he View>Customize menu.

 

Actually, that's not true. I use coherence on my MBP with an external monitor, where the MBP LCD is at 1440x900, and the external display is at 1600x1200. The Coherent display ends up being 3040x900, so the coherent display spans the two monitors but I lose the top of the 16x12 external display (mac applications will go there, but windows apps in paralles don't.)

I suspect the three display problem is related to going over 4096 pixels wide, which is a windows display size limit...
-Brent

 

I'm guessing the reason it works for you is that both displays "compromise" on a resolution. I can tell you that having the internal display on a MB at 1280x800 and an external at 1280x1024 just craps out with the exact warning the OP mentioned.

 

I run Coherence with my MBP and an external display and span both screens w/o any problems. The MacbookPro runs at 1440 x 900 and the external LCD monitor at 1280 x 1024. The resulting display size is 2720 x 900. So not all of the vertical height of the external display is used.

My only gripe about Coherence is that it seems to suck a lot more CPU and memory than just running an OS window....

 

Eureka... sort of. Coherence working on multiple monitors.

You may have something here. I just installed Parallel's on a 3-GHz Mac Pro (dual quad processors) connected to three 20" monitors, each with a resolution of 1680 x 1050. I'm getting the same error message when trying to use coherence to extend over the multiple monitors...

"Unable to switch to Coherence Mode. Primary operating system does not support screen resolution requested by guest operating system. Select another resolution for the guest operating system or review your video system configuration."

So my extended Mac OS desktop is configured as 3*1680 x 1050, or 5040 pixels wide and 1050 pixels deep... notice that 5040 is bigger than 4096...

... but on reading your statement about the 4096 windoze limit, I reconfigured my monitors for two across and 1 below, an extended desktop size of about 3360 x 2100 overall... and guess, what? It finally started working!! Had to reduce the color level support, but hey, it works... very annoying however.

So I see two problems which will have to be overcome to make Coherence work with multiple monitors. a) the 4096 limit needs to be overcome (is it there in Vista?) and b) the max video memory needs to be increased well beyond 32Meg to support huge desktops.

Thanks for you tip!

 

The 32MB limit may very well be part of the issue but the larger issue is how each monitor is represented even within 32MB. I've posted another note about the vertical height issue. BTW I know of no such 4096 pixel wide limitation in Windows per se and I do know that others have supported 3 and even more monitors within Windows. Those solutions tend to use speciality video cards and so are only possible with desktop computers, not laptops.

 

Definiely not correct!

I have an iMac 20" resolution 1680 * 1050 and a Samsung resolution 1280 * 1024 and Coherence works like a gem independent of the Parallels setting for a secondary display.

 

Will experiement a bit more

Hm, all I know is that with 3360x2100 Mac OS extended desktop size (in a "T" shape), Coherence went from being non-functional to being "somewhat functional"... I still did have trouble with the color depth and I'm still playing with that, but I have some other things to try:

1) I can select under System Preferences for the sum total horizonal width of the monitors to be less than 5140 (3 at max resolution side by side) to get it under 4096... to see if 4096 really is come kind of magic number.

2) I can disable one of the monitors (I have the 3rd monitor in use sometimes on an old G4 Quicksilver anyway, shared via the monitor's input select switch, which I reserve for a few OS9 applications I still need, VGA only though, not DVI).

3) I'm considering installing XP and BootCamp to see if it has trouble with all three displays running without Parallel's at all. Don't like this prospect, but I'm an electrical engineer and the CAD software I want to run on my Mac almost demands 3 monitors... (one for schematics, one for PCB/FPGA layout design, and another for various simulation utilties). At least two monitors min, but three is peachy.

I also have a 37" 1080P Spectre monitor/HDTV (1920 x 1280 or something like that) that I want to vesa mount on the wall just above the 3 lower 20" screens for a 4th monitor to do a little multimedial production work next month, but that's later. Again, it would be really nice if Parallels would handle all the monitors. Better yet, I would like to see parallels have an option to select which monitors it can use (for example, 2 for Windows and 2 for the Mac OS) just like you can specify which DVD-R drive you'd like to assign... under "add new hardware". Coherence would solve all of this, but still the flexability would be nice.

Al