Crossfire Question

**BrokenApe** · 02-09-11, 01:27 AM

Folks I've heard that with ati's crossfire and cards of a similar series for example HD 48** I can combine say a 4870 and and 4850 or 4890 unlike with nvidia's SLI where the cards would have to be of the exact same type... has anyone here tried this with cards of a simliar nature and if so its it reasonably workable? (no more then the usual crossfire/ati issues *wry grin*) thinking of buying a basic 4850 to try with my 4870 and get a few more fps/shinies till tax returns come in later this year when I can get a better setup

**HeavyG** · 02-09-11, 03:14 AM

This is true. But always remember the old saying "The carriage will only go as FAST as the SLOWEST horse". This saying applies directly to Crossfire. Basically, you would be under-clocking your 4870. This is fine as you will still see better performance with the Crossfire setup than with a single, higher clocked 4870.

I ran dual 4850s for over a year and they ran most games great. I upgraded so I could run DX11, but for DX9 and DX10 games, they ran most stuff with more than acceptable frame rates.

**BrokenApe** · 02-09-11, 05:35 AM

Aight, thanks man I plan on going with something in crossfire in perhaps the hd 6000 series later but having everything slow down during major gun battles and with most of the shinies turned off... well it's just irritating so a few bucks for a used 4800 series will help tide me over

**Kanati** · 02-09-11, 08:37 AM

I ran two 4850s and a 4890 in crossfire. Ran pretty well. As Heavy said, the 4890 was underclocked to match the 4850s. The plan was to pull the 4850s and swap in two more 4890s eventually... But I wound up going nvidia so it never happened.

**Phyrelight** · 02-09-11, 09:05 AM

that is one of the major advantages of ATI in my opinion. The ability to string the cards together is especially useful when new ATI cards come out and you can pick up the older ones dirt cheap. Grab a couple and toss them in crossfire and you have great FPS for half the cost. I am a fan of nvidia myself.

**maximusboomus** · 02-09-11, 09:12 AM

Can I add a question... I plan to get a second 5870 this year most likely, would my 750W be sufficient? i5 12GB machine.

**Phyrelight** · 02-09-11, 09:16 AM

Originally Posted by maximusboomus

Can I add a question... I plan to get a second 5870 this year most likely, would my 750W be sufficient? i5 12GB machine.

I think 750W is pushing your luck.

Power Consumption : ATI Radeon HD 5870: DirectX 11, Eyefinity, And Serious Speed

this shows the power consumption of the different cards. 354W under load for one, 141W idle. For crossfire with 2 cards that jumps to 561W under load. You would need to run a power consumption tool on your system to see what you are currently pulling. Depending on the efficiency of your PS (ie silver, gold etc) it will determine it. I would recommend a 1000W PS for anything CrossFire/SLI personally unless you have a top rated PS with 80+ percent efficiency rating.

edited to be clearer....check your current draw. That that draw and subtract it from 750* the efficeincy of your PS and you get your safe available power.

example. If you are currently pulling 550w with processor, ram and GPU and your PS is 80% rated then your safe power consumption with spikes is .80*750 = 600W

600W-550W=50W of safe power draw available.

You DO NOT want to pull more than the efficiency rating on your PS or you run the risk of blowing something in your system.

To add a second card to this example above you need an addition 207W (561-354) to put in another card in crossfire so you would need to add an additional 207-50= 157W of power and on a 80 percent efficient PS that would be 200W to get 160W after the 80 efficiency so you would need 950W PS with an 80% rating.

**BrokenApe** · 02-09-11, 05:15 PM

for budgetary concerns as well as performance, when I built my current machine I went with antec's CP-1000 series power supply it only fits in certain of their cases, but I can't hear it, it stays cool and it's performed like a champ so if you've got one of those handfull of cases that can hold it (weird size p/s) then I'd recommend that being several dollars less then the equivalent rating watts wise on regular size items