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Nergol · 04:15 PM

So I wonder if anyone can help explain this.

I have an early 2011 MacBook Pro 13". When operating normally and not attached to any external devices, the CPU runs at around 40-50C (all temps provided by iStat). When at my desk and attached to my external hard drives and USB hub (and a cooling pad), it runs at around 60C. Add my external monitor (a humble 17" Dell, connected via a MiniDisplay Port - DVI adapter cable), and that adds a few degrees, getting it up close to 70C (all temps measured after I'd been running in that configuration for at least ten minutes).

So in a general rearrangement of my desk a few days ago, I decided to try turning my monitor 90 degrees into portrait mode. From then on, my CPU started running at about 85C, with the fan running constantly at 4-5000RPM, and a noticeable general slowdown in the system (dragging windows around became stuttery, and so on). These all manifested almost immediately after boot - zero to broiling in a couple of minutes. The strange thing is, I saw no increase in CPU or RAM usage. My system just got hotter and slower.

I tried running with everything else but the monitor plugged in, and temps were normal. I turned the monitor back into landscape mode, and voila - my CPU temps and performance went back to normal.

So I'm back in landscape mode for the foreseeable future, but it still kind of bugs me that I have no explanation for this very bizarre-seeming issue. Can anyone else offer any explanation for it?

Thanks, all.

ibook_steve · Mar 30, 2012, 07:37 PM

Very weird. Operating in portrait doesn't add any resolution and shouldn't strain the CPU or GPU in any additional way.

One thing to try might be resetting the PRAM at boot with the external display attached in portrait. Hold cmd-option-p-r until you hear the boot chime twice. See if this makes a difference.

Steve

Waragainstsleep · Mar 31, 2012, 03:11 PM

Not all GPUS have always supported display rotation that way so perhaps there is more to the process than we suspect. I must be generating the display output as usual and then converting it to go sideways on the fly.