Maximum Resolution for prospective 'retina' screens

[sammich]

Hope this hasn't been brought up before, but here goes:

The following assumes that between now and when the new 'retina' displays are introduced next month or so, the Thunderbolt spec won't be updated.

The maximum useful throughput (goodput) for the current TB spec is 8Gbit/s per direction/per channel (8b/10b encoding). This is below DisplayPort 1.0/1.1 spec of 8.64Gbit/s.

What this means is that there is a ceiling on the size of the display that can be driven with a Thunderbolt cable. And seeing as the TB Display is Apple's flagship external display, it will likely see updates to the resolution, matching, or at least exceeding other displays available in Apple's range. If Apple's brand new 'universal port' spec that they championed, and had a headstart with, couldn't work with their new high resolution updated TB Display, why bother with updating the display resolutions at all.

So, with all that out of the way, the maximum resolution is:

3072 x 1728.

60 fps * (3 * 8) bit colour * 3072 * 1728 = 7.644 Gbit/s.

This is all sheer speculation, but grounded in my form of logic. There's nothing stopping Apple from using 'retina' displays in internal screens that are beyond the size above, but to me it just doesn't sit right. Suppose a new Mac Pro is released and all Apple sells are these new 5120x2880 TB displays but you're forced to run them at 2560x1440 because that's all that TB can supply. You could argue that the GPU's in them would have their own later spec DisplayPort that would drive them at full res...but no spec handles that amount of data.

How much data?

60 fps * (3 * 8) bit colour * 5120 * 2880 = 21.23 Gbit/s. You'd need two HDMI 1.4 spec cables, or 3 TB cables to power that beast.

 

[Ashok0]

DisplayPort 1.2 has a throughput of 17.28Gbps. It supports 60Hz * 30bpp * 3840 * 2160 = 14.9Gbps. The new ZOTAC GeForce® GTX 680 has a DisplayPort 1.2 output and supports a 3840x2160 resolution. Technically Apple could release a 4K iMac now, all they would need to do is add a DP1.2 port or respec Thunderbolt to use DP1.2.

 

[sammich]

DisplayPort 1.2 has a throughput of 17.28Gbps. It supports 60Hz * 30bpp * 3840 * 2160 = 14.9Gbps. The new ZOTAC GeForce® GTX 680 has a DisplayPort 1.2 output and supports a 3840x2160 resolution. Technically Apple could release a 4K iMac now, all they would need to do is add a DP1.2 port or respec Thunderbolt to use DP1.2.

Can't respec. Thunderbolt carries the display data and TB is limited to 10Gbit/s throughput. Means that DP has to fit in that.

But as I said, Apple should be supporting their own standard, not leaping back and forth, confusing people, especially if they try to daisy chain these displays.

 

[Ashok0]

Can't respec. Thunderbolt carries the display data and TB is limited to 10Gbit/s throughput. Means that DP has to fit in that.

But as I said, Apple should be supporting their own standard, not leaping back and forth, confusing people, especially if they try to daisy chain these displays.

Yeah... that being said, isn't Thunderbolt supposed to scale up to a theoretical maximum of 100Gbps with optical cables? Obviously that isn't going to happen over night, but Apple has hinted it won't be locked at 10Gbps forever.

 

[sammich]

Yeah, that's on the roadmap...just not by next month, which is when everyone is expecting 'retina' displays all around.

 

[ajr9]

Thunderbolt can go into DisplayPort-only mode

According to wikipedia, Thunderbolt is backwards compatible with DisplayPort 1.2. So if a TB port detects a DisplayPort device connected, it will "provide a native DisplayPort signal with 4 lanes of output data at no more than 5.4 Gbit/s per lane". However, if a Thunderbolt device is connected, then DisplayPort data will be intermixed with PCI data, capped at 10Gb/s, as sammich has said.

So, Apple could do a 27" Retina display, but it wouldn't be Thunderbolt -- DisplayPort only. And while Apple is still making the 27" Cinema Display (in support of the only non-Thunderbolt that Apple sells, the Mac Pro), it seems odd that Apple would go "backwards", and make a new display that doesn't have all of the whizzy options that the 27" Thunderbolt display provides.

This is a bit of a bummer. It means that unless Apple does something proprietary (which isn't totally out of the question for Apple), the best we could hope for at WWDC is retina MacBooks and possibly a retina iMac. But no Mac mini or Mac Pro.

 

[Mr. Retrofire]

So, with all that out of the way, the maximum resolution is:

3072 x 1728.

60 fps * (3 * 8) bit colour * 3072 * 1728 = 7.644 Gbit/s.

...

How much data?

60 fps * (3 * 8) bit colour * 5120 * 2880 = 21.23 Gbit/s. You'd need two HDMI 1.4 spec cables, or 3 TB cables to power that beast.

Apple uses ARGB in iOS and Mac OS X, not only RGB. So replace 3 with 4.

 

[sammich]

Apple uses ARGB in iOS and Mac OS X, not only RGB. So replace 3 with 4.

But the display has no use for an alpha channel, right? Wouldn't a final RGB value be calculated and sent?

 

[Randomoneh]

It seems like it's 32 bits per pixel if we trust these quotes from Wikipedia (without sources):

"Many modern desktop systems (Mac OS X, GNOME, KDE, Windows XP/Vista/7, etc...) offer an option for 24-bit truecolor with 8 bits for an alpha channel, which is referred to as "32-bit color". When switching to an 8/16/24-bit color option in those systems, generally transparency/translucency effects are disabled, and the only reduction in color depth is seen when going to 8/16-bit color."

and

"A typical computer monitor and video card may offer 8 bits of resolution (256 output levels) per R/G/B color channel, for an overall 24-bit color space (or 32-bit space, with alpha transparency bits, which have no bearing on the output resolution)."

 

[JacaByte]

Transparency is handled by the graphics card. (Or at least it should be...)