October24

Using your 27" iMac as a Display - How it works.

Tags: | Categories: Apple | Hardware | Mac OSX | Miscellaneous | Windows 7
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Well...  I did it.  I was trying to decide whether I wanted to buy a 24" LED Cinema display to hook to my 17" Macbook Pro, or whether I just wanted to buy one of the new iMacs and do the same.  Silly, I know, but then again - so is Apple's new pricing model.  I'm kind of excited to see what kind of product lineup they come up with for their cinema display line - because now that the 27" iMac contains a beautiful 2560x1440 LED Backlit display at a pricepoint $100 below the 30" Cinema display - one has to wonder who would actually buy the 30" display now.

Well - at least, that's how I justified it.  The iMac is a great machine and I've already installed Windows 7 RTM on it, but 90% of the time I'll be using it as a display for my MacBook Pro.  Since they announced this new product line - I've been searching for information on how the single Mini DisplayPort will function as both an input and output.  Scouring around the net - I saw that many people had the same simple question that no-one (even Apple dweebs in the stores) can answer.... "When you use it in display mode, does the iMac have to be turned on?"

Well - For me - that was the $1600 question.....  and here is the answer - Yes, the iMac must be turned on.  In fact, you must actually boot completely into Snow Leopard before it will "switch" into display mode.    I've run through a couple of different scenerios, and it seems that in all of them - the graphics card in the iMac is actually performing the input/output translation - and it appears that it is doing so with the aid of drivers present in Snow Leopard.  So... to summarize - here are some of the scenerio's I've tried - and what happens:

  • MacBook Pro off, iMac off.  I Connected the MBP to the iMac via Belkin DisplayPort cable, and powered both systems on.   Both systems booted independantly into their default OS (Mac OS in my case) and the MBP did not recognize the iMac as an external display until I unplugged the DisplayPort connector and plugged it back in, at which time everything instantly switched to the iMac as an external monitor.
  • MacBook Pro on, iMac off.  I Connected the MBP to the iMac and then powered the iMac on.  The iMac swiftly booted into MAC OS, and again, did not switch to display mode until I unplugged and replugged the cable.
  • MacBook Pro on and booted into Leopard, iMac on and booted into Snow Leopard.  Plugged in the cable - iMac instantly switched to display mode and the Macbook instantly recognized it.
  • MacBook Pro on and booted into Windows Vista 64-bit, iMac on and booted into Windows 7.  Plugged in the cable - nothing.  nada.  zilch.  Which is what lead me to my conclusion that something in the drivers in Snow Leopard make this a possibility.
  • Macbook Pro on and booted into Windows Vista 64-bit, iMac on and booted into Snow Leopard.  Plugged in the cable - iMac instantly switched to display mode and the Macbook instantly recognized it..... Yup.... Snow Leopard definately has something to do with it.

So.  Before I bought the machine tonight - the dweeb at the apple store assured me that when you plug in the iMac, it "sleeps" the PC and only runs the display.   I might buy that it sleeps the hard drive - but from everything I can tell, the iMac brain is still running, and needs to be running, in order for the display hardware to receive, decode, and display the digital DisplayPort connector.  It seems that this is also the case simply due to the amount of heat coming out of the vents on the iMac - if it were only the display - I can't imagine it would be running as hot as it is.

Unfortunately, I'm pretty sure that's not what most people want to hear.  It's certainly not what I wanted - but.... at the pricepoint (slightly less expensive than the 30" studio display with only 3" diagonal and 160 vertical pixel defecit) - it's definately worth a look still.  You get yourself a kick ass monitor that includes a kick ass PC that performs very well in Snow Leopard and Windows 7.

Hopefully I've taken some mystery out of the $1600 question for you ;)

Comments

25/10/2009 03:48 #

Thanks for the info. I've been wondering the very same thing since I found out about the input capability.

For the sake of nerdiness, I'd suggest you try a power-meter (I can't remember the English word for it, but I'm sure you know what I mean. The thingie you plug into the wall, and plug your device into, and then read the wattage/power consumption) - Perhaps that could give an idea about whether or not the iMac sleeps, hibernates, is in standby or has little dwarfs dancing on the desktop...

Once again. Thank you very much for info. I have one question though.

Could you supply me with some information on whether or not it would/could be possible to connect - let's say - a Playstation 3 to the iMac? I mean. With dual-boot and a PS3 it could be the ultimate center of media and entertainment.

Thanks again.

Regards
Allan, Denmark

PS.: Sorry for bad English and possible typos Smile

NoNigDK Denmark

25/10/2009 05:03 #

Great suggestion... I even have one of those "kill-a-watt" devices that could be used to test this very thing. I'll try that soon and post the results.  Information on the kill-a-watt can be found at www.p3international.com/.../P4400-CE.html

As for using it as a display for your PS3, I'm pretty sure it could be done - but I looked all over the net and was not able to find a cable to go from HDMI to DIsplayPort - although I find many cables which go from DisplayPort to HDMI.

I am not sure if these are simple cables with a pinout difference on the connector, or if there is some kind of circuitry in them to allow the conversion of the displayport signal to be displayed on a HDMI monitor. If there is no circuitry involved, then I would not see why one of these cables would not work. If there *is* circuitry involved in conversion, you'll need a HDMI to Mini DIsplayPort cable.

Basically, One would think it will work perfectly - you just need the proper cable. As to whether that cable exists yet or not - I'm not sure, but it might.

rjnedved United States

25/10/2009 05:18 #

So i- I just followed your suggestion for a really quick test.  I shut down the iMac, plugged my kill-a-watt device in-line, and then booted it back up.  Once things settled down, the system was pulling about 140-145 watts of power on average.  I plugged it into the Macbook Pro, waited until  it began operating as an external display for the Macbook Pro and then waited another 30-45 seconds to allow time for things to possibly shut down or sleep on the iMac "brains" side of things.....

The result... 140-145 watts as a display.  This tells me that the PC itself is *not* going into instant sleep mode.  I will do some further testing by lowering my sleep settings on the PC side of things to see if it ever "goes to sleep"....  but at first glance, it looks like the iMac itself is always running as earlier believed due to the heat generation while running as a display.

I'll post more detailed results later.

rjnedved United States

26/10/2009 10:23 #

Thank you for testing it. So 140-145 Watts, that's about the same as the max. power consumption of their 30 inch Cinema Display. My own Eizo S2411 draws about 110 Watts, at max.

I had hoped it was more around 90-100 Watt-ish. The 30 inch Syncmaster 305T is about 130 Watts, as far as I can remember.

Regarding the PS3, I'd hoped that I could do some HDMI -> DVI, DVI -> Minidisplayport conversion. If it would work with a TV connected that way, then why not the PS3? I have to do some research on that.

But thanks again Smile

NoNigDK Denmark

02/11/2009 03:09 #

So, as you say it seems that there is software - Snow Leopard making the switch. Is there a key combination that will flip it from monitor to computer? I was thinking of using that as a monitor, but then thought it would be a good headless server (can you remote the iMac while using it as a monitor?). Also, would like to be able to switch to the computer without unplugging the cable. is that possible?

dan United States

03/11/2009 05:25 #

See my follow-up post from today for answers to your questions - www.nedvedtech.com/.../...display-a-Follow-up.aspx

rjnedved United States