SLI and Crossfire Questions

  • Thread starter Thread starter Gabriel Knight
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Gabriel Knight

Hi all, I know if I have two 3D cards in either SLI or Crossfire that the
rendering is split in half to the two cards to process but does two 2 gig
cards give a total of 4 gigs? or does it remain at 2 gigs? Thanks GK.
 
Gabriel said:
Hi all, I know if I have two 3D cards in either SLI or Crossfire that the
rendering is split in half to the two cards to process but does two 2 gig
cards give a total of 4 gigs? or does it remain at 2 gigs? Thanks GK.
Click to expand...

Remains at 2GB from a texture storage perspective.

From an address space perspective (i.e. working out whether
you need a 64 bit OS or not), the address space needed is
still 4GB. Basically, it's like two identical copies are
loaded, a copy of data structures for each card. The
effective storage ("how much stuff a users game can store"),
is limited to 2GB. But while the OS/DirectX/games are
working with the video cards, both cards need to be addressed
uniquely, so 4GB of address space is needed.

With a decent amount of system RAM, such a system might be
in the 8GB address space vicinity (say 4GB address on video,
4GB of space for the system RAM), and needs a 64 bit OS.

In exceptional cases, the BIOS actually made some mistakes
on this issue. Some early PCI Express motherboard, the BIOS
decided to open both a cached address space and an uncached
address space for the video cards. With two 2GB video cards,
that would have required 8GB of address space, just for
the video cards. That seems to be fixed on more modern stuff,
and only one space is opened per card. So if I plugged
your two cards into my dual slot motherboard, it would
use 4GB of address space now.

Paul
 
Hi all, I know if I have two 3D cards in either SLI or Crossfire that the
rendering is split in half to the two cards to process but does two 2 gig
cards give a total of 4 gigs? or does it remain at 2 gigs? Thanks GK.
Click to expand...

I have to say, if this is for your friend's new gaming rig, you are
going about it the wrong way. With a $600 total budget, your friend is
far better off getting one good graphics card instead.

When I built a new rig last year, I ended up spending $190 on my
motherboard, $160 on my SSD, $100 for RAM, and $270 on the CPU. Notice
how that's already $720, and does not include the case, PSU, CPU fan,
extra case fans, or graphics card.

Basically your friend's budget is too low for SLI/Crossfire. He needs
a budget of about $1300 before buying dual graphics cards. Anything
less than that, and he is better off getting upgrading some other part
of his system.

The main reason for such a high threshold is that a $300 graphics card
will out perform two $150 graphics cards in SLI/Crossfire format. So
the only reason to go SLI/Crossfire is when you are buying top end
graphics cards. And there's no reason to get top end graphics cards
without a top end CPU/motherboard to go with them.
 
Hi Ting, thanks for the reply but you misunderstood my post what I said was
he had $500 to $600 for the motherboard to play with but thanks. GK.


Hi all, I know if I have two 3D cards in either SLI or Crossfire that the
rendering is split in half to the two cards to process but does two 2 gig
cards give a total of 4 gigs? or does it remain at 2 gigs? Thanks GK.
Click to expand...

I have to say, if this is for your friend's new gaming rig, you are
going about it the wrong way. With a $600 total budget, your friend is
far better off getting one good graphics card instead.

When I built a new rig last year, I ended up spending $190 on my
motherboard, $160 on my SSD, $100 for RAM, and $270 on the CPU. Notice
how that's already $720, and does not include the case, PSU, CPU fan,
extra case fans, or graphics card.

Basically your friend's budget is too low for SLI/Crossfire. He needs
a budget of about $1300 before buying dual graphics cards. Anything
less than that, and he is better off getting upgrading some other part
of his system.

The main reason for such a high threshold is that a $300 graphics card
will out perform two $150 graphics cards in SLI/Crossfire format. So
the only reason to go SLI/Crossfire is when you are buying top end
graphics cards. And there's no reason to get top end graphics cards
without a top end CPU/motherboard to go with them.
 
Hi Ting, thanks for the reply but you misunderstood my post what I said was
he had $500 to $600 for the motherboard to play with but thanks. GK.
Click to expand...

Having $500-600 for just the motherboard (and presumably the CPU to go
with it), is pretty much being budget-unconstrained. Many high-end
options are available at this stage.

Yousuf Khan
 
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