Mac Mini noticably laggy when using dual monitors

[zzappbrann]

Hello!

I've got a late 2009 Mac Mini 2.26ghz, 2gb RAM, 9400M 256mb VRAM that I hooked up two monitors to: One Samsung 24" 245B (Via the MiniDVI) and one 20" DELL 2005fpw (Via MiniDisplayPort to DVI). I've also tried the MiniDVI/MiniDisplayport the other way around.

If I only have the 24" Samsung connected everything is very smooth and enjoyable but when I connect both of the displays (extended desktop) things like moving/resizing a window around, using exposé, spaces becomes much (or slightly) more laggy/choppy. I would expect 256mb of VRAM to be enough seeing how I had both of these monitors connected to my old PC with less VRAM without problems. (Maybe you can't compare old non-GPU accelerated XP to OS X...)

I've also tried to run both the monitors on a lower resolution without any improvements. Searching google for this issue has yielded me nothing.

Any ideas on how to fix/further troubleshoot this? Anybody with similar issues?

BR
John

[saul]

First I've heard of this problem. Two monitors works just fine for me but mine are smaller.

Check to see if you have any 3rd party screen drivers (SwitchResX, etc.) that might be interfering.

Also - if you do mirroring, do you see the same lag?

[zzappbrann]

Thanks for your quick reply, no I don't have any third party display drivers installed.

I used the term "much more laggy" before, that was probably an overstatement, its only slightly more laggy.

From what I can see mirroring works fine (no lag).

I also downloaded and tried the program "ATI NVIDIA Tool v 0.93" that displays the amount of free VRAM according to it I have plenty of free VRAM, even with both displays connected (> 100mb)

Where did you hear of this problem before? Any links?

[JohnnyBoy]

I'm running two HP 20 inchers out of the back of my Mini, and this is also the first that I've heard of this problem.

The only time that moving windows around gets slightly "stuttery" on this machine is when I'm dragging a window from one screen to the other -- it's noticeably smoother when the window remains on the same screen.
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[saul]

I know that on Windows there was an issue with complex background images. Can you try changing the background to a solid color?

Otherwise it is time to ask Apple directly.

[zzappbrann]

It might just be my imagination, but changing the background to a solid colour instead of a picture made it feel less sluggish... I wonder why though...

Thanks for all the help!

[DannySmurf]

This sounds more like a lack of RAM than a video problem (remember video RAM is shared with the system in that model... and you only have 2GB). If your computer is starved for memory, that could put pressure on the video system as well.

Do you have some spare RAM lying around that you can temporarily use to bump that machine to 4GB? I have a feeling doing that may solve your problem. My wife's older mini was slightly sluggish with only 2GB of RAM, with only a single monitor connected.

[zzappbrann]

Buying more RAM is definitely on my TODO list! It looks like the price of a single 4gb module is going down...

But if your assertion were true, wouldn't I experience the same sluggishness when running out of RAM with just one monitor attached?

No, sorry I don't have any DDR3 ram laying around! If I had, I would put it in my Mini right away, permanently.

[zzappbrann]

I decided to stop being a cheapskate and just go out and buy one single 4gb memory stick...

It turns out that DannySmurf was actually right, most of the lag problems just disappeared! I guess 2gb of RAM nowadays just isn't enough.

So I currently run one 4gb Corsair DDR3 1066mhz stick combined with one of my old, preinstalled 1gb Hynix 1066mhz sticks, bringing the combined memory to 5gb. Works great!

Thanks again for your help.

[JohnnyBoy]

[DannySmurf]

[quote="zzappbrann"]I decided to stop being a cheapskate and just go out and buy one single 4gb memory stick...

It turns out that DannySmurf was actually right, most of the lag problems just disappeared! I guess 2gb of RAM nowadays just isn't enough.

So I currently run one 4gb Corsair DDR3 1066mhz stick combined with one of my old, preinstalled 1gb Hynix 1066mhz sticks, bringing the combined memory to 5gb. Works great!

Thanks again for your help.[/quote]

Glad to help. Regarding not seeing the sluggishness with a single monitor... memory problems are not a simple black-and-white issue to solve. Lots of factors come into play: how much stuff is actually on the screen, what's on the screen but behind something (which gets dumped to system RAM, not video RAM), how much work the video card is actually doing (if it's working too hard, more stuff becomes inactive and gets bumped to system RAM, increasing memory pressure), whether the CPU is able to move data between memory and the video card at an appropriate speed... etc.

Your setup was probably perfectly adequate to drive a single display, given your pattern of usage. But adding the second monitor either outran your video card, which couldn't get more memory from the system, or just caused too much inactive junk to be dumped into system RAM, which caused the rest of the hardware to have to spend an increasing amount of time clearing the memory backup that was created.