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How will having two graphics cards effect my Mac?

MythicFrost

MythicFrost

macrumors 68040
Original poster
Mar 11, 2009
3,944
40
Australia
I'm wondering how two graphics cards work?

(I have a 23i Mac monitor)

I'm thinking of two ATI Radeons HD 4870 512MB, I'd prefer one card with just 1GB, will they act the same, they both have a lot of memory? will only one cards memory be used, and the second card just sit there never doing anything?

Or will it use both cards memory, just like if I had a 1GB card?

Kind Regards
Me
 
Oh so the other cores in my Mac, can use both :confused:, this is one area where I'm completely clueless... I wish Mac could use SLI/Crossover

Kind Regards
Me
 
MythicFrost said:
Oh so the other cores in my Mac, can use both :confused:, this is one area where I'm completely clueless... I wish Mac could use SLI/Crossover

Kind Regards
Me
Click to expand...

I think you need a little explaining.

GPUs (Graphics Processing Units) are processors of Graphics. This means that they have a clock speed, base clock, etc etc. Basically, anything you find in a CPU + RAM setup, you'll find in the GPU.

So most GPUs these days have lots of cores. If you have 1 card thats 32 cores (for example) then you have 32 cores. However if you have 2 cards both with 32 cores, then you have 64 cores in total, but still retain the memory that is added together.

This is why RAM spread across more modules is better, because you get the clock speed of the RAM hypothetically doubled (dual-core in a sort of way)

Hope this explains everything.
 
I see, so two ATI Radeons 4870's will have double the cores in them, and 1GB of total memory between them for my computer to use?

Interesting, so that's good, I think I understand, having two is the same as having one ATI Radeon 4870 1GB (if it existed).

If I have a lot graphics to be drawn, it won't just use one card (512MB) it will use two if necessary (1GB) something like. =D

Kind Regards
Me
 
MythicFrost said:
I see, so two ATI Radeons 4870's will have double the cores in them, and 1GB of total memory between them for my computer to use?

Interesting, so that's good, I think I understand, having two is the same as having one ATI Radeon 4870 1GB (if it existed).

If I have a lot graphics to be drawn, it won't just use one card (512MB) it will use two if necessary (1GB) something like. =D

Kind Regards
Me
Click to expand...

They don't share memory. Each GPU get's it own 512MB for itself. Also, a 1GB 4870 would have half the cores of two 512MB 4870s, but they would all be able to use all 1GB. Again, sharing of VRAM between cards is not allowed. And the 1GB 4870 does exit, btw.

It won't use two cards, just the one. The other can only drive displays. Crossfire is meant to allow it use both, but OS X doesn't support it. Not to mention, most stuff can't take advantage of it unless it specifically designed to anyway.
 
Alright, so it just sits there, the second card?

I'll look for the 1GB ATI, if you could provide a link, I'd appreciate it..

Edit: I can't seem to find one (the 1GB)

Also, is there a 1.5GB ATI Radeon HD 4870?

Kind Regards
Me
 
J the Ninja said:
They don't share memory. Each GPU get's it own 512MB for itself. Also, a 1GB 4870 would have half the cores of two 512MB 4870s, but they would all be able to use all 1GB. Again, sharing of VRAM between cards is not allowed. And the 1GB 4870 does exit, btw.

It won't use two cards, just the one. The other can only drive displays. Crossfire is meant to allow it use both, but OS X doesn't support it. Not to mention, most stuff can't take advantage of it unless it specifically designed to anyway.
Click to expand...

Forogt about this. Lost in SLi world.
 
MythicFrost said:
Alright, so it just sits there, the second card?

I'll look for the 1GB ATI, if you could provide a link, I'd appreciate it..

Edit: I can't seem to find one (the 1GB)

Also, is there a 1.5GB ATI Radeon HD 4870?

Kind Regards
Me
Click to expand...

Apple only sells the 512MB version. There is no 1.5GB version. What do you need all that VRAM for anyhow?
 
1GB would be fine then, it will be used in adobe cs4 with some heavy graphics stuff, final cut pro, motion, etc...
and I also have vram dedicated to my virtual machine in Parallels 4.0, and intend to have more, so I need plenty.

How can I buy the 1GB version, if I do, will my Mac Pro still be under warranty?

Kind Regards
Me
 
MythicFrost said:
1GB would be fine then, it will be used in adobe cs4 with some heavy graphics stuff, final cut pro, motion, etc...
and I also have vram dedicated to my virtual machine in Parallels 4.0, and intend to have more, so I need plenty.

How can I buy the 1GB version, if I do, will my Mac Pro still be under warranty?

Kind Regards
Me
Click to expand...

Sorry, but at present there are no graphics cards available for the MacPro '09 which has 1Gb or 1.5Gb of Video RAM. Maybe someday, in the distant future some third-party will produce one but don't hold your breath.

I'm not sure where you've read stuff, but adding one or more graphics cards to your Mac system doesn't combine the memory. Even on a PC with X-fire or SLI enabled, it still doesn't combine the video ram of the two cards.

By the way, neither SLI or X-Fire are supported on the Mac, it's a windows only thing.
 
I have Mac Pro 08, and I thought J the Ninja, said there is an ATI Radeon HD 4870 1024MB?

512MB isn't enough vram, I need to dedicate a MIN of 128MB for my Windows XP Virtual Machine in Parallels 4.0, and I'll be getting Vista soon, which might be the same, if not 256MB, I will only have 128MB to 256MB left on the card for the Mac Pro... which isn't enough

Kind Regards
Me
 
I think.. that you have too much money. With regards to your last post, perhaps you should try to read some of the posts that have been made in your thread and try to comprehend them. Your questions have all been answered. There's no way to do what you want to do.
 
(Edited)

J the Ninja
......
They don't share memory. Each GPU get's it own 512MB for itself. Also, a 1GB 4870 would have half the cores of two 512MB 4870s, but they would all be able to use all 1GB. Again, sharing of VRAM between cards is not allowed. And the 1GB 4870 does exit, btw.
......

I understand that two graphics cards do not do anything, other than supporting more monitors, I need the ATI Radeon 4870 1024MB, does it exist or not? I'm a little confused, J said it was o_O

Hah, too much money, not even close, I just need a better graphics card, and one that has more memory

Kind Regards
Me
 
There is indeed a Radeon HD 4870 with 1GB of fast video ram onboard but it's only for PC. It won't be available for the Mac until someone figures out a way to flash the card with a combined BIOS. Standard PC firmware doesn't work in a Mac, this is the main thing that prevents PC graphics card from working under the OSX environment.

Perhaps, instead of ranting on about how you'd like more video ram, it'll be more constructive for you to learn about flashing standard PC cards and making them work on your Mac? Then maybe you'll be able to satisfy your needs and provide proof there's is a 1GB HD 4870 for Mac.
 
Not ranting, just trying to find out what I need to know, so I don't end up buying this, and then, hey there's this better thing out there, flashing standard pc cards? I don't know what that means, but it sounds like it might void the warranty for my Mac, I don't know want anything that has to be modified and fiddled with, I guess I'll just have to accept the 512MB ati radeon

Thanks for all your help guys

Kind Regards
Me
 
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