How important is memory bandwidth interface?

Memory bandwidth is important. How the bandwidth is achieved is not.

The 4870 only has a 256 bit interface because it uses 3600MHz GDDR5. This gives it a bandwidth of 115GB/s. For comparison, your 8800GTS has a 320 bit interface with 1600MHz GDDR3. Although you have a larger bus width, the memory speed is vastly slower, and as a result, your bandwidth is only 64GB/s. (Note though that because of the added bus width, your memory bandwidth is higher than half that of the 4870, despite the memory clock speed being lower than half of the 4870's). Basically, what is important is a combination of the bus width and the memory clock, and the 4870's insane 3.6 GHz memory clock more than makes up for the slight deficiency in bus width.

according to newegg.com the 4870 has a memory clock of 4000mhz are you saying 3600 because thats the actual speed? also, what is ramdac? all the cards i compare have the same ramdac also can someone please explan steam processors? the 4870 claims to have 800 while my 8800gts has only 96 that seems like a big jump!

Ramdac basically handles certain conversions and does not affect performance. They've been @ 400mhz for years now. Basically ramdacs (from my limited understanding) handle the physical connection to the monitor.

As for the 4870. 3600mhz is stock speed but some brands sell their cards with overclocked memory at 3800mhz to 4400mhz normally. At 3600mhz it delivers 115gb/s which is far more than is actually needed at this point in time. The 4850 memory interface is about half of the speed and it handles high definition gaming...

so... i havent bought a ati card in along time... i always bought nvidia and i dont know much about HIS as a brand name for ati chipset however, from what i understand they are all pretty much the same is that true? also, how do you all feel about HIS as a brand compared to diamond, palit, sapphire, and others?

Most ATI brands are manufactured by the same handful of manufactures and just have brand stickers and perhaps custom cooling installed. I've heard HIS is a good brand and sometimes offers superior cooling.

However I've never bought one of products so I can't say from first hand experience.

from my understanding (i quickly googled this today... coincidence?  ) RAMDAC's handle the amount of colours and the speed at which they are transmitted to the monitor. apparently they are unnecessary with HDMI and such interfaces though. made in 1990 by IBM or something, and was stolen and used in every other graphics card since ^.^

Just wondering, why are you going for the 1GB version? I suppose you are using a 24" screen or bigger?  

Try reading this http://www.extremetech.com/article2/0,2845,2309870,00.a... it explains the bandwidth differances pretty well.
Also you cant compare stream processor counts between the companies as they are differant things, what ATI call a SP and what Nvidia call an SP are very differant.
His are a very good compant quality wise, they do cost more but in my experiance its worth it. I have had three of there ICEQ cooler cards now and they run really cool compared to a standard card.

Mactronix

^ +1 what this guy said.

RAMDAC is the Digital to Analog Converter. Reading up on it, it's a little more confusing than I thought lol. I always figured it was an onboard device that converted the digital information in to an analog signal. Wrong! -.-

No, i only have a 20" monitor. But I would feel stupid going from a card with 640mb to one with only 512mb on top of that the 1gb 4870 is only a little more than the 512mb one. I would go with the 2gb x2 if i thought it would fit in my case.

So... are you saying that if i dont have at least a 24" screen the 1gb card wont work? or it wont do all it can or what? by the way, here are my system specs.

Vista Ultimate x32
AMD Phenom x4 9950 be
Msi k9a2 platinum
1wd hdd w/500gb & 1 toshiba hdd w/350gb
4gb ocz memory
8800gts 640mb grap card
samsung dvd burner
Kingwin Steel case
Zalman cnps9700 cooler (i think its 9700 i know the old i took out was 9500 this one i think is 9700)
1000 watt cooler master power supply
razer deathadder mouse
$15 hp keyboard LOL

after the new video card my next step is to add a wd velocoraptor hdd for games and another for windows only. I will probably keep the 500gb wd for music and pics.

I will take suggestions from anyone!

http://www.guru3d.com/article/amd-ati-radeon-hd-4870-1024mb-review/8

you'll see improvements even with middle resolutions (19"-22") depending on the game, of course.

The 1GB will work just fine. It doesn't give as much improvement over the 512mb at lower resolutions, but in every case, it will be at least equal to the 512 MB version.