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At Apple's introduction of the new 27-inch iMac with Retina 5K Display, Phil Schiller noted that the machine's $2499 starting price compares favorably with some of the higher-end 4K displays on the market today for closer to $3000, leading some to wonder whether it would be feasible to use the iMac as an external display for something like a Mac Pro.

For a number of years, iMacs have supported a feature known as target display mode, which allows them to serve as external displays for other computers, but as pointed out by TechCrunch's Matthew Panzarino yesterday, the new Retina 5K iMac does not support this mode.

imac_retina_waterfall.jpg
The probable reason for this is also likely the reason why Apple did not announce a standalone Retina Thunderbolt Display yesterday: bandwidth limitations. The current DisplayPort 1.2 specification used over Thunderbolt 2 on Apple's latest Macs simply isn't capable of handling the bandwidth necessary for 5K video over a single cable.

As a result, no current Mac, including the Mac Pro and Retina MacBook Pro models that do support 4K displays, can currently drive a 5K external display. Technically, Apple could allow another Mac to output video at a lower resolution and have the Retina iMac scale the content up to fit its display, but this would not be ideal and Apple has apparently elected not to support it as an option.

As noted by Marco Arment, simple plug-and-play support for 5K external displays over a single cable will need the new DisplayPort 1.3 standard, but that won't be an option until Intel's Skylake platform, the successor to the upcoming Broadwell family, is launched.
Doing it right will require waiting until DisplayPort 1.3 in Thunderbolt 3 on Broadwell's successor, Skylake, which isn't supposed to come out for at least another year -- and Intel is even worse at estimating ship dates than I am, so it's likely to be longer. [...]

I'd estimate -- granted, I'm wrong a lot -- that Apple won't ship a standalone 5K display until at least 2016, and it won't work with any of today's Macs, including the 2013 Mac Pro.
Arment points out that Dell's upcoming 5K display uses dual DisplayPort 1.2 cables for connectivity but that no current Macs appear to support the setup and even if they did performance would likely not be ideal.

Another potential product on the horizon is a Retina 21.5-inch iMac likely at 3840 x 2160 pixels, although it is unclear when Apple plans to launch such a machine. KGI Securities analyst Ming-Chi Kuo predicts a second half of 2015 launch for the machine in a similar pattern to that seen with the MacBook Pro, where the larger 15-inch model received a Retina display option a number of months before the 13-inch model followed suit.

Article Link: Retina 5K iMac Will Not Act as External Display, Standalone Apple 5K Display Unlikely Soon
 

Eweie

macrumors regular
Oct 5, 2013
152
84
Why would you want to? I doubt anyone would like to connect their windows pc this beauty to use it as a monitor lol.
 

sputnikv

macrumors 6502a
Oct 3, 2009
506
3,184
I go by this:

If I had to guess, you’ll have a long wait, and they won’t work with any Mac sold to date.

Panel yields may be tight for a while, and external displays are a low priority for Apple. The original 27” iMac’s groundbreaking LCD panel wasn’t available in an external display from Apple for almost a year after its release. But that’s not the biggest problem.

Pushing this many pixels requires more bandwidth than DisplayPort 1.2 offers, which is what Thunderbolt 2 ports use for outputting video signals. (I wrote about this a few times.) Doing it right will require waiting until DisplayPort 1.3 in Thunderbolt 3 on Broadwell’s successor, Skylake, which isn’t supposed to come out for at least another year — and Intel is even worse at estimating ship dates than I am, so it’s likely to be longer.

It may be possible to use two DisplayPort 1.2 or Thunderbolt 2 cables to power a 5K display, but only if the GPU could treat each port as its own full-bandwidth DisplayPort 1.2 channel, the sum of which represented one logical display, and had the panel combine and properly sync the two at the other end.1 I don’t think any of the current Macs can do this, including the Mac Pro — MST to run 4K panels at 60 Hz only seems to be supported within individual ports, not spanned across two.

I’d estimate — granted, I’m wrong a lot — that Apple won’t ship a standalone 5K display until at least 2016, and it won’t work with any of today’s Macs, including the 2013 Mac Pro.
 
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HenryDJP

Suspended
Nov 25, 2012
5,084
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United States
better throw away that 5k monitor/computer in 5 years when 5k finally becomes a standard.

Well in 5 years I'm sure many people will upgrade to the latest model of this machine anyway.

I guess Apple wants the Mac Pro users to get a 3rd party 4K display. Not a problem. Not everybody has to have an actual Apple display to use the Mac Pro.
 

Sonmi451

Suspended
Aug 28, 2014
792
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Tesla
Why can't they rig some kind of dual thunderbolt adapter to give it the necessary bandwidth?

Too bad, but I don't really need a 5k display anyway. maybe next year.
 

NICKXXXXXX

macrumors regular
Oct 9, 2014
215
29
Well this sucks. I really wanted a screen for my macbook pro retina when I use it at home. Do you think there is any chance that they will release an updated Thunderbolt display though? With like usb 3.0 etc. HDMI and obviously thinner.
 
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sputnikv

macrumors 6502a
Oct 3, 2009
506
3,184
Well in 5 years I'm sure many people will upgrade to the latest model of this machine anyway.

I guess Apple wants the Mac Pro users to get a 3rd party 4K display. Not a problem. Not everybody has to have an actual Apple display to use the Mac Pro.

If they released a 5k display, only the Mac Pro would be able to output to it. Then they would have to advertise that it doesn't work with macbooks or the mac mini... it's a headache. Not worth it.
 

J. Jizzle

macrumors regular
Mar 30, 2013
231
79
U.S.A.
I was thinking about getting one... Until I saw the price! No thanks, Apple. I can buy two 27" iMacs for practically the price of one 5K Retina iMac. 5K isn't really needed at this point in time, since there aren't any devices that can record in 5K. There aren't really many on the market that can even record in true 4K, so I'm going to wait a while
 

reedog117

macrumors newbie
Feb 6, 2012
29
3
No! I wanted to hook up my TiVo to this to prevent having to buy a new TV for my home office!
 

ipearx

macrumors member
Sep 18, 2005
65
12
New Zealand
I'd like to see a 4K 24" display in the meantime. Sure a 27" retina would be nice, but if it's just not possible to drive at the moment, then so be it. Give me a smaller one!
 

JHankwitz

macrumors 68000
Oct 31, 2005
1,911
58
Wisconsin
Why can't they rig some kind of dual thunderbolt adapter to give it the necessary bandwidth? Too bad, but I don't really need a 5k display anyway. maybe next year.

Exactly the point. A second 5K display isn't needed or desired by 99% of the Mac buyers. Apple no longer wants or needs to make products for the 1%ers.
 

JackANSI

macrumors 6502a
Feb 3, 2011
558
413
Well in 5 years I'm sure many people will upgrade to the latest model of this machine anyway.

I guess Apple wants the Mac Pro users to get a 3rd party 4K display. Not a problem. Not everybody has to have an actual Apple display to use the Mac Pro.


Apple's 4K/5K display would probably have to cost around $4000 and it wouldn't sell in massive numbers anyway since a lot of people looking for that type of display have already bought something else...
 

JHankwitz

macrumors 68000
Oct 31, 2005
1,911
58
Wisconsin
I was thinking about getting one... Until I saw the price! No thanks, Apple. I can buy two 27" iMacs for practically the price of one 5K Retina iMac. 5K isn't really needed at this point in time, since there aren't any devices that can record in 5K. There aren't really many on the market that can even record in true 4K, so I'm going to wait a while

They're only 25% more than the old model, but the extra $500 for the 5K may not be worth it for most users.
 

britboyj

macrumors 6502a
Apr 8, 2009
814
1,086
Well I guess I won't be getting 5K iMac then. Makes things a bit cheaper on my wallet.

I use a Hengedock for my work MBP at home that lets me combine workstations with the flick of a switch. This is a deal breaker for me, albeit an understandable one.
 

guzhogi

macrumors 68040
Aug 31, 2003
3,725
1,804
Wherever my feet take me…
I have a 15" rMBP for personal use and a 13" non-retina MBP for work, and I can't really tell the difference. I don't know if if I have bad eyesight, or just don't care. Meh.

However, the article says Thunderbolt 3 will support DisplayPort 1.3. Will it also support PCIe 3, or better yet, 4? As PCIe 3 supports 128b/130b encoding while PCIe is 8b/10b, we'd get far better throughput due to lower overhead (1.54% versus 20% overhead).
 
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