We just got done with our hands-on time with Apple’s new products, and we’ll start with what’s likely the sneakiest of them, the iMac with Retina Display.

Why “sneaky”? The answer is all in the HiDPI display, which Apple calls the “Retina 5K Display”. The retina display is definitely the star of the new iMac, as the rest of the hardware is largely a minor specification bump from last year’s model. In fact turned off you’d be hard pressed to tell the difference between the 2013 (non-retina) and new retina models, but the screen is immediately evident once on.

At 5120x2880 pixels, the new Retina 5K Display is precisely 4x the pixels of the 2560x1440 panel in last year’s model. What this means is that Apple can tap their standard bag of tricks to handle applications of differing retina capability and get all of it to look reasonably good. This also means that 2560x1440 content – including widgets – will scale up nicely to the new resolution. Apple does not discuss whom they have sourced the panel from, but given the timing it’s likely the same panel that is in Dell’s recently announced 27” 5K monitor.

Much more interesting is how Apple is driving it. Since no one has a 5K timing controller (TCON) yet, Apple went and built their own. This is the first time we’re aware of Apple doing such a thing for a Mac, but it’s likely they just haven’t talked about it before. In any case, Apple was kind enough to confirm that they are driving the new iMac’s display with a single TCON. This is not a multi-tile display, but instead is a single 5120x2880 mode.

This also means that since it isn’t multi-tile, Apple would need to drive it over a single DisplayPort connection, which is actually impossible with conventional DisplayPort HBR2. We’re still getting to the bottom of how Apple is doing this (and hence the sneaky nature of the iMac), but currently our best theory is that Apple is running an overclocked DisplayPort/eDP interface along with some very low overhead timings to get just enough bandwidth for the job. Since the iMac is an all-in-one device, Apple is more or less free to violate specifications and do what they want so long as it isn’t advertised as DisplayPort and doesn’t interact with 3rd party devices.

Update: And for anyone wondering whether you can drive the 5K display as an external display using Target Display Mode, Apple has confirmed that you cannot.

Meanwhile driving the new display are AMD’s Radeon R9 M290X and R9 M295X, which replace the former NVIDIA GTX 700M parts. We don’t have any performance data on the M295X, though our best guess is to expect R9 285-like performance (with a large over/under). If Apple is fudging the DisplayPort specification to get a single DisplayPort stream, then no doubt AMD has been helping on this matter as one of the most prominent DisplayPort supporters.

The rest of the package is very similar to the 2013 iMac. It comes with an Intel Haswell desktop class CPU paired with 8GB or more RAM, 802.11ac support, and Apple’s SSD + HDD Fusion drive setup. Apple now offers a higher speed CPU upgrade option that goes up to 4GHz (4.4GHz Boost) – likely the Core i7-4790K – that should make the high-end iMac decently more performant than last year’s model by about 10%.

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  • SirKnobsworth - Wednesday, October 22, 2014 - link

    Because you can't drive that many pixels over a single external connection.
  • milleron - Friday, October 17, 2014 - link

    If one wanted to use a 2560 x 1440 secondary display connected by Thunderbolt, would it be necessary to get the upgraded GPU with 4GB of video RAM or might the R9 M290x with 2GB be sufficient?
  • milleron - Saturday, October 18, 2014 - link

    Hope that's not just boilerplate text copied and pasted from the features list of prior iMacs.
  • GC2:CS - Saturday, October 18, 2014 - link

    Holy **** an 27" screen with 200 ppi....
  • repoman27 - Sunday, October 19, 2014 - link

    In case anyone missed iFixit's teardown ( https://www.ifixit.com/Teardown/iMac+Intel+27-Inch... ), the TCON is a semi-custom chip made by Parade for Apple. The DP665, as it's marked, looks to be an 8-lane eDP 1.3 timing controller with PSR.

    So if the GPU isn't treating the display as two separate tiles and using two separate DP 1.2 outputs, the sneaky bit would be how Apple managed to get a single display controller and digital encoder / transmitter block to support 5120x2880, and then bind both links of a UNIPHY transmitter block into a single 8-lane eDP interface. I guess this works fine with TMDS for Dual-Link DVI, so maybe it was possible all along for DisplayPort as well. It's odd to think that Pitcairn can pull off driving a 5120x2880 panel as a single tile though.

    I'm guessing the flexibility of AMD's digital encoder / transmitter blocks and PHYs is the primary reason Apple went with their GPUs for the Retina iMac.
  • houkouonchi - Saturday, October 25, 2014 - link

    I am kind of curious if they are just doing something like running at 18-bit color (6bpc) with dithering or something. Not even using that extreme of timings (regular cvt-r) one can run 5120x2880 @ 60Hz via a 938 Mhz pixelclock which is within spec of what DP 1.2 can do @ 6 bpc (limit is 960 Mhz). The 8bpc limit is 720 Mhz pixel clock and if they are staying true to that no timings would be capable of of fitting it in 720 Mhz as absolutely 0 extra blanking would still be 884 Mhz pixelclock.
  • repoman27 - Sunday, October 26, 2014 - link

    Yeah, but like I said, if you look at the teardown photos which show the TCON, it's pretty clearly an 8-lane eDP job, which is more than enough for 5120x2880, 24 bpp, 60 Hz using HBR2. I seriously doubt they would double the number of signaling pairs between the GPU and TCON unless they were actually using them.
  • likethesky - Wednesday, November 5, 2014 - link

    Hey repoman27 or others ~

    What I'm wondering--for future proofing purposes, as I'm about to drop over $3k on one of these--is: Do you or others you might check in with think it's possible and therefore probable that a third party or perhaps software upgrade from Apple will allow this iMac to be used in *4k* (yes, 4, not 5) Target Display Mode at some point? That'd at least be a nice consolation prize for having bought early and getting to use it with computer at 5k now, knowing that at some point--even with the DP 1.2, unlikely to ever be upgradable--that this could be used as a secondary 4k display, at the least?

    I'd love to know the answer to that question.
  • jporomaa - Tuesday, October 21, 2014 - link

    will anandtech do some benchmarking on it?
  • odedia - Friday, October 24, 2014 - link

    I'm waiting for this review any day. This is the only thing that keeps me from ordering this machine!

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