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Retina 5K iMac is going to lag like crazy

D

ddarko

macrumors 6502
May 7, 2007
290
61
OurDarkness said:
I have just visited http://www.esp.com and it seems that the images fade in. The fade in is gradual and smooth in my laptop. Can you test it on a different riMac?
Click to expand...

Moved to a regular 27" iMac, 3.5ghz i7/8gb/4gb 780M. You're right, the same thing happens with espn.com on this machine. Also went to nytimes.com and saw same phenomenon of half-images before fully loading. So I was premature to attribute it to the 5k pixels, it may be the wifi speed here at the store, it's about 7mbit download according to speedtest.net. However, I do think there is still a difference when scrolling really fast down this thread's page - the regular iMac seems smooth versus some tiny jerkiness with the retina iMac. I dunno, this is one person's impression.

Also, Safari is having trouble correctly displaying the layout on the retina iMac. On espn, all the text on the homepage is extra big and overlapping.
 
Last edited:
L

leenak

macrumors 68020
Mar 10, 2011
2,416
52
ddarko said:
Moved to a regular 27" iMac, 3.5ghz i7/8gb/4gb 780M. You're right, the same thing happens with espn.com on this machine. Also went to nytimes.com and saw same phenomenon of half-images before fully loading. So I was premature to attribute it to the 5k pixels, it may be the wifi speed here at the store, it's about 7mbit download according to speedtest.net. However, I do think there is still a difference when scrolling really fast down this thread's page - the regular iMac seems smooth versus some tiny jerkiness with the retina iMac. I dunno, this is one person's impression.

Also, Safari is having trouble correctly displaying the layout on the retina iMac. On espn, all the text on the homepage is extra big and overlapping.
Click to expand...

I went to espn.com and don't see anything extra big/overlapping on my iMac. I also haven't experienced any jerkiness.
 
theSeb

theSeb

macrumors 604
Aug 10, 2010
7,466
1,893
none
kwijbo said:
Happy to be corrected, what math are you using to come to ~14 Gb/s?
Click to expand...

Absolutely no idea mate :) The reason why I questioned your post is purely because I have read that 4K requires more than your figure. (I posted one of the quotes from Anandtech to support that earlier).

Then again, thinking about, I have been reading goobledy gook, since DP 1.3 will have 25.9 Gbps effective bandwidth and that is enough to drive 2 x 4K displays. :eek:
 
H

houkouonchi

macrumors regular
Oct 31, 2005
134
0
theSeb said:
As far as I understand it, to run a 4K 24 bpp display at 60 Hz requires ~ 14 Gbps. I could be wrong, but everything I have read tells me that I am not.
Click to expand...

The problem is he isn't taking into account the blanking. Here is the standard HDMI 2.0 4k@60Hz modeline:

Modeline "3840x2160_60" 593.40 3840 4016 4104 4400 2160 2168 2178 2250 +hsync +vsync

so with blanking its 4400x2250.

This is 14.256 Gigabits.

So you are correct as no display (that I know of) can run with absolutely 0 blanking. You can do reduced blanking to lower that. here is a cvt-r (CVT standard timings with reduced blanking):

# 3840x2160 @ 60.00 Hz Reduced Blank (CVT)
# field rate 60.00 Hz; hsync: 133.31 kHz; pclk: 533.25 MHz
Modeline "3840x2160_60.00_rb" 533.25 3840 3888 3920 4000 2160 2163 2168 2222 +HSync -Vsync


so 4000x2222 which is 12.79 gigabits. This is about a minimum level. You can sometimes go lower than CVT-R but usually not much lower before you start having signal issues.

Here is 5k (22.52 gbps) @ 8 bpc:

# 5120x2880 @ 60.00 Hz Reduced Blank (CVT)
# field rate 59.99 Hz; hsync: 177.70 kHz; pclk: 938.25 MHz
Modeline "5120x2880_60.00_rb" 938.25 5120 5168 5200 5280 2880 2883 2888 2962 +HSync -Vsync

Just 1 DP 1.2 is actually capable of driving this... just not at 8 bpc. DP also supports increasing pixel clock and lowering from 8 bpc to 6 bpc. At 6 bpc the DP 1.2 pixelclock limit is 960 Mhz (so this 938.25 Mhz pixelclock mode just barely fits in it). At 8 bpc the limit is 720 Mhz though so it definitely exceeds spec @ 8bpc.
 
theSeb

theSeb

macrumors 604
Aug 10, 2010
7,466
1,893
none
houkouonchi said:
The problem is he isn't taking into account the blanking. Here is the standard HDMI 2.0 4k@60Hz modeline:

Modeline "3840x2160_60" 593.40 3840 4016 4104 4400 2160 2168 2178 2250 +hsync +vsync

so with blanking its 4400x2250.

This is 14.256 Gigabits.

So you are correct as no display (that I know of) can run with absolutely 0 blanking. You can do reduced blanking to lower that. here is a cvt-r (CVT standard timings with reduced blanking):

# 3840x2160 @ 60.00 Hz Reduced Blank (CVT)
# field rate 60.00 Hz; hsync: 133.31 kHz; pclk: 533.25 MHz
Modeline "3840x2160_60.00_rb" 533.25 3840 3888 3920 4000 2160 2163 2168 2222 +HSync -Vsync


so 4000x2222 which is 12.79 gigabits. This is about a minimum level. You can sometimes go lower than CVT-R but usually not much lower before you start having signal issues.

Here is 5k (22.52 gbps) @ 8 bpc:

# 5120x2880 @ 60.00 Hz Reduced Blank (CVT)
# field rate 59.99 Hz; hsync: 177.70 kHz; pclk: 938.25 MHz
Modeline "5120x2880_60.00_rb" 938.25 5120 5168 5200 5280 2880 2883 2888 2962 +HSync -Vsync

Just 1 DP 1.2 is actually capable of driving this... just not at 8 bpc. DP also supports increasing pixel clock and lowering from 8 bpc to 6 bpc. At 6 bpc the DP 1.2 pixelclock limit is 960 Mhz (so this 938.25 Mhz pixelclock mode just barely fits in it). At 8 bpc the limit is 720 Mhz though so it definitely exceeds spec @ 8bpc.
Click to expand...

Thank you for the detailed explanation. :)
 
D

ddarko

macrumors 6502
May 7, 2007
290
61
leenak said:
I went to espn.com and don't see anything extra big/overlapping on my iMac. I also haven't experienced any jerkiness.
Click to expand...

This is what it looked like at the store:

RtEdKrV.jpg
 
L

leenak

macrumors 68020
Mar 10, 2011
2,416
52
ddarko said:
This is what it looked like at the store:
Click to expand...

It looks like someone messed with the font size on that system. My font for espn.com is much smaller than that. I will say the page looks normal to me, it might be a setting someone did and the espn page can't handle it.
 
5

5iMacs

macrumors regular
Oct 25, 2014
176
13
sth said:
This seems to be a problem with Yosemite in general and is not iMac specific. Happens on other Macs as well (incl. non-retina ones).
Click to expand...

After a week with Yosemite and 2 days with the 5k iMac base GPU, I am coming to the same conclusion.
 
K

kwijbo

macrumors regular
Jan 28, 2012
249
131
houkouonchi said:
The problem is he isn't taking into account the blanking. Here is the standard HDMI 2.0 4k@60Hz modeline:

Modeline "3840x2160_60" 593.40 3840 4016 4104 4400 2160 2168 2178 2250 +hsync +vsync

so with blanking its 4400x2250.

This is 14.256 Gigabits.

So you are correct as no display (that I know of) can run with absolutely 0 blanking. You can do reduced blanking to lower that. here is a cvt-r (CVT standard timings with reduced blanking):

# 3840x2160 @ 60.00 Hz Reduced Blank (CVT)
# field rate 60.00 Hz; hsync: 133.31 kHz; pclk: 533.25 MHz
Modeline "3840x2160_60.00_rb" 533.25 3840 3888 3920 4000 2160 2163 2168 2222 +HSync -Vsync


so 4000x2222 which is 12.79 gigabits. This is about a minimum level. You can sometimes go lower than CVT-R but usually not much lower before you start having signal issues.

Here is 5k (22.52 gbps) @ 8 bpc:

# 5120x2880 @ 60.00 Hz Reduced Blank (CVT)
# field rate 59.99 Hz; hsync: 177.70 kHz; pclk: 938.25 MHz
Modeline "5120x2880_60.00_rb" 938.25 5120 5168 5200 5280 2880 2883 2888 2962 +HSync -Vsync

Just 1 DP 1.2 is actually capable of driving this... just not at 8 bpc. DP also supports increasing pixel clock and lowering from 8 bpc to 6 bpc. At 6 bpc the DP 1.2 pixelclock limit is 960 Mhz (so this 938.25 Mhz pixelclock mode just barely fits in it). At 8 bpc the limit is 720 Mhz though so it definitely exceeds spec @ 8bpc.
Click to expand...

Thanks for chiming in - that was very helpful. Is the CVT mode determined by the panel, GPU or interface? It seems that DP supports CVT and CVT-R?

Looks like DP 1.3 brings the bandwidth down a hair more with CVT-R2.

theSeb said:
Absolutely no idea mate :) The reason why I questioned your post is purely because I have read that 4K requires more than your figure. (I posted one of the quotes from Anandtech to support that earlier).

Then again, thinking about, I have been reading goobledy gook, since DP 1.3 will have 25.9 Gbps effective bandwidth and that is enough to drive 2 x 4K displays. :eek:
Click to expand...

After doing some reading on what houkouonchi described, it seems DP 1.3 supports CVT-R2 which decreases the bandwidth needed even further (12.54 Gb/s for 3840*2160*24*60) so that just squeezes 2 streams in.
 
theSeb

theSeb

macrumors 604
Aug 10, 2010
7,466
1,893
none
kwijbo said:
Thanks for chiming in - that was very helpful. Is the CVT mode determined by the panel, GPU or interface? It seems that DP supports CVT and CVT-R?

Looks like DP 1.3 brings the bandwidth down a hair more with CVT-R2.



After doing some reading on what houkouonchi described, it seems DP 1.3 supports CVT-R2 which decreases the bandwidth needed even further (12.54 Gb/s for 3840*2160*24*60) so that just squeezes 2 streams in.
Click to expand...
Thank you. Very interesting stuff to cram into my brain. :)
 
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