iMac 27" with AMD Radeon Pro 570 4 GB, 575 4 GB, and 580 8 GB - 8 GB necessary for dual 5K displays?

[Eug]

I'm curious. I ordered the iMac with 8 GB Radeon Pro 580 just because it was only double digit $ more than the 575 with 4 GB. (I ordered the i7-7700K and these were the two GPU options available.)

For now I'll be using one 27" 5K (internal) HDR display with one (external) 27" SDR 2560x1440 display, but the intent is to eventually get a second 5K display, for dual 5K HDR displays once the pricing on these comes down.

I don't game and I don't do VR. Some mainly 2D media applications. eg. Some photo / video editing with some 3D accelerated filters.

Are both the 580 and it's 8 GB video RAM total overkill? If so, how much power and VRAM are actually needed?

 

[nathanddrews]

The amount of GPU memory required for the display buffer itself is miniscule. If a graphics card from 10 years ago had a modern display output, it could do the job.

((horizontal pixels * vertical pixels * number of bits per pixel color) / (8 to convert bits to bytes * 1024 to get KB * 1024 to get MB))

5K 10-bit:
((5120 * 2880 * 30) / (8 * 1024 * 1024)) ~ 53MB

((5120 * 2880 * 40) / (8 * 1024 * 1024)) ~ 71MB (including alpha channel)

This is, of course, before the RAM itself is filled with assets from whatever application you're using (including the OS).

 

[Eug]

Note that they are 10-bit displays. So, let's say there a few apps applications open and perhaps a dozen 20 MP images too.

With some 3D filters and such, what would one need? 2 GB? Would the faster GPU make any noticeable difference for video filters?

Not that it really matters. The way they price these machines, if you're getting the 7700K, you may as well get the 580 as well.

 

[nathanddrews]

Note that they are 10-bit displays. So, let's say there a few apps applications open and perhaps a dozen 20 MP images too.

With some 3D filters and such, what would one need? 2 GB? Would the faster GPU make any noticeable difference for video filters?

I accounted for the 10-bit display in the calculation (10-bit = 10 bits per R, per G, per B = 30 bits per pixel (before adding 10 more for alpha)).

The GPU RAM will only be used if the application you use is GPU accelerated, otherwise all the performance will come down to your CPU and system RAM. For functions that utilize the GPU, it will behave according to its abilities - faster GPU will render filters faster, more RAM will enable smoother previews for longer time frames, etc. You might want to poke around on the Apple/Mac forums before making your purchase to ensure that you're getting the right setup for your needs. Most pro video and photo editors I know focus mostly on maximum CPU speed/cores and system RAM and don't invest tons into GPUs, but there are always going to be exceptions depending upon certain applications and plugins used.

 

[wilds]

You seem like someone who keeps their PC's for a long time. The RX 580 won't seem like overkill in a few years but rather adaquate for smooth dual 5k performance.

8 GB of VRAM is overkill but 4 GB is not one bit. It is very easy to use 4 GB of VRAM nowadays. 8 GB will age very well on OS X.

 

[Guru]

It doesn't really matter. Even 1GB would be sufficient enough to run any video or images, etc... Now whether you are using one or two monitors or more, it depends on the application what amount of vram you are going to use.

So gaming will obviously be the biggest vram user.

 

[Eug]

Yes I do keep my machines a long time. My current machine is a Lynnfield Core i7 from 2010. That one has a Radeon HD 5750 with 1 GB RAM. That machine lagged somewhat with photo libraries and editing software even back then but I suspect it had to do more with the CPU and the platter drive. Definitely time for an upgrade.

Truthfully I was just more curious about the VRAM than anything, as the cost here is not really a significant factor. These machines are not cheap, but because of limited configuration options, once you make the choice to go for the i7-7700K, the price difference between the 575 4 GB and the 580 GB isn't that much. With some configuration combinations in the US the difference in price for the 575 vs 580 comes out to just $20 or even $0.

http://tidbits.com/article/17286

In Canada it ended up being about a US$64 difference, but because this is being partially expensed as a business expense, my additional personal out of pocket cost is less than US$40 so I figured why the hell not. Their upselling strategy worked on me I guess.

The only negative I can see is that the 580 can likely use way more power at peak load, but then again I suspect its idle power usage probably isn't that much more than the 575.

The other reason I was asking is it now impossible to configure such a machine with less than 4 GB. 4 GB comes with the base model GPU. Given that multimedia creation types that like iMacs do much more 2D stuff than 3D, I found that a bit odd.

BTW, here are the specs of the cards:

http://creators.radeon.com/radeon-pro/

Reading around the net it seems with its 217 GB/s memory bandwidth, the Radeon Pro 580 represents a downclocked Radeon RX 580, making it a mid-rangish or upper mid-range card.

 

[Mopetar]

I'm curious. I ordered the iMac with 8 GB Radeon Pro 580 just because it was only double digit $ more than the 575 with 4 GB. (I ordered the i7-7700K and these were the two GPU options available.)

Are both the 580 and it's 8 GB video RAM total overkill? If so, how much power and VRAM are actually needed?

I actually just bought the exact same iMac (using it right now) as you to replace the practically ancient iMac (early 2008 model) I was using prior to that. It was pretty much relegated to being a bedroom television and web surfing machine, but it was definitely feeling its age.

I don't think the GPU will be overkill, because Apple has been pushing Metal a lot and I expect that applications will be able to make a lot more use of it. I'm assuming that Apple's apps already make use of the GPU as much as they can, but I suppose it depends on what you'r using.