the question is simple and clear, is any big difference between PCI x16 and PCI x4, I want to go CrossFire with Radeon HD 5770 on a Gigabyte GA-MA785GT-UD3H motherboard, so will I get FULL CROSSFIRE?

another question: every <600w PSU will handle Crossfire?

Simple answer is NO, your Crossfire will be slightly crippled- as to how much, maybe not a lot. For a definative answer you'll have to search for Motherboard/Crossfire (and SLI) reviews based around a PCIe x16, PCIe x4 board such as:
Giagbyte P55-UD3R/-UD3/-UD3P (and the P55A versions), MSI P55-CD53, ASRock P55 Pro/P55DE/P55DE3 Pro, Asus P7P55D/ P7P55D LE, EVGA P55 LE and any AMD boards (sorry, I'm lazy and AMD chipsets hold no interest for me).
As for power supply AMD recommend a 600 watt for Crossfired HD 5770- that seems a little overkill since the cards are TDP rated at 108 watts each. ASSUMING that you aren't running a massive overclock and have a usual setup ( 1-3 harddrives, 1 or 2 optical drives and some USB peripherals and case fans) then a GOOD (branded) 520-550 watt would suffice. As with any system- buying a piece of crap cheapo psu is a quick way into trouble. Stick with a good a brand: Corsair, OCZ, Enermax, PC Power & Cooling, Silverstone, Gigabyte all make well regarded PSU's, while certain models within the Thermaltake, Antec and Cooler Master lines offer a good alternative.

BTW : Why Crossfire HD5770 over a single HD5850 - surely the single card is cheaper, and offers better performance.

Why yes indeed...x16 has four times the bandwidth of x4 no?

It is an old article, but I think it is very telling:
http://www.tomshardware.com/reviews/...s,1572-10.html

Keep in mind those tests are using an 8800GTS, which delivers FAR less information than a 5770.

What brand power supply are you using? Amps? (or link?)

Way to go hellokitty- with cherrypicked pages like that you have a fine career ahead of you as a PR flak for AMD or nVidia. I think a review based on the PCIe 2.0 standard might be a little more applicable in this case rather than the Fred Flintstone era PCIe 1.0- so how about we try this http://www.tomshardware.com/reviews/...-2.0,1915.html
With the increased bandwidth offered by the PCIe 2.0 standard you'll see that the differences are lessened considerably.

the only reason why 5770 is because is cheaper, and the crossfire is for future. For components I decided to get rid of optical drive and wil have max 2 HDD and maybe an usb peripheral.

PSU is the biggest problem for me, I don't want to pay more than 60 euros on PSU, but I still know is one the most important pieces of a good PC, I was thinking of GLACIALTECH GP-AL650A and gigabyte odin 720(when I saw it it had a reasonable price, but can't find it right now) or PC Power & Cooling Silencer 610W, any other suggestions will be very very welcomed.

On motherboard side it appears that the x4 PCI will cramp a little bit my crossfire but I can't find another board with just one x16 line with a significant price drop, so most probably I'll stick with this one.

Thanks all of you for provided links!

You would be fine with any of these three power supplies. As for any others that might be suitable, that will depend on local pricing and availability. Corsair is usually priced competitively wherever it's sold.

thanks, now I know that all my PSU choices are not as bad as I thought.

As always this is the best forum!

PCI-E 2.0 x4 has the same bandwidth as PCI-E 1.1 x8, so for a card like the 5770, it would make very little difference, if at all.

This test shows a 5870 tested at all the PCI-E 2.0 speeds, and at x4, it is at 95% of its peak performance limit; the 5770 is a weaker card, so it shouldn't lose any performance at all IMO.

As for PSUs, the PCP&C and Gigabyte units are a better choice compared to the GlacialPower one, in that order. You can also go for the Corsair 450VX (which is an excellent unit) if you need a PSU urgently, but you'll need to get a more powerful one later if you upgrade to anything beyond your current card.

Lol ok bad post ^^, in fact I was almost sure PCIE x4 was a different size too...

PCI-E x4 slots are a different size mate, but the available bandwidth is double that of PCI-E 1.1, which allows for significantly better performance.

well.... I'm very impressed, I thought it will loose more performance than just 5 %, but in order to keep cost on minimum I decided to go with micro ATX motherboard and no Crossfire for the future, I think 5770 will last me at least 2-3 years with decent performance and in 2-3 years a lot of things will change.

BTW: You guys are awesome!!!

I see...

Just for clarification for anyone following this thread.
PCIe x 4 is a short, sometimes openended slot.
PCIe x 16 that only has only 4 PCIe lanes afforded it mechanically is a full length PCIe x 16 slot.
It is typically the second full length slot on budget P45/P35 boards as well as any 975X boards.
If the P45 board has three full length slots and no NF200 chip then either the 2nd or 3rd slot will be 4 lanes and cannot be populated with a GPU if the two primary graphics slots are occupied.

I will throw this into the mix. I know from research and hands on experience that the PCIE 4X 2.0 will not take a performance hit in your situation, more than enough bandwidth.

thanks, but as I sad earlier in order to reduce cost I will go micro ATX with one PCI x16, I think for me will be enough power.