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Bus Width Vs Frequency Vs Memory

Last response: in Graphics & Displays
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May 7, 2009 6:45:01 PM

Hi All,
I am a first time buyer of graphics card. I have made up my mind on 4770 Sapphire reference card. Comparing the specs of 4770 Vs 4850 how much will bus width matter. I mean to ask does bus width help higher resolution or higher settings (as in high details Vs Medium details OR no AA vs 4xAA).

Thanks
Santosh
a b U Graphics card
May 7, 2009 6:51:03 PM

Bus width doesnt matter on its own.

Bandwidth is a product of memory speed and bus width. DDR5 memory is quad pumped, ie bandwitch is frequency*bus*4. DDR3 is double.

A 4850 and 4770 use different types of memory. the 4770 uses quad pumped GDDR5, the 4850 only GDDR3. The 4850 has double the bus width.. but the same effective memory transfer rate.
a c 130 U Graphics card
a b } Memory
May 7, 2009 7:00:09 PM

Performance wise they are very similar but the 4770 uses less power and is newer tec, thats why i would pick it over a 4850.

Mactronix
Related resources
May 8, 2009 1:13:21 AM

Thanks Daedalus685 and mactronix
a b U Graphics card
May 8, 2009 3:03:43 PM

It depends really, although in general performance, its a push.

A higher Bus width allows for the transfer of more data per LOAD operation. In theory, a 256-bit GPU can access 4x as much data as a 64-bit CPU in a single LOAD operation (hence, why CPU's tend to be clocked higher, to allow for more LOAD operations to compensate for a small data bus).

Provided the GPU can execute all its data in a single cycle, the higher bus width would clearly be faster. Of course, that almost never happens, so most of the data needs to be stored in RAM, where faster RAM speeds then start to close the distance.

Hence theres almost no diffrence between the two approaches, at least in current applications. I suspect that purley mathematical functions, as opposed to rendering, would run much faster on a wider bus though (maybe the reason ATI refuses to implement Physx? Because NVIDIA's larger Bus would be too big an advantage in benchies? )
March 5, 2010 10:30:17 PM

daedalus685 said:
Bus width doesnt matter on its own.

Bandwidth is a product of memory speed and bus width. DDR5 memory is quad pumped, ie bandwitch is frequency*bus*4. DDR3 is double.

A 4850 and 4770 use different types of memory. the 4770 uses quad pumped GDDR5, the 4850 only GDDR3. The 4850 has double the bus width.. but the same effective memory transfer rate.


Daedalus685... I am curious if your video card is running DDR2 would you simply times by one?

ShayneNeal at gmail dot com
a b U Graphics card
March 5, 2010 11:06:03 PM

No, DDR, DDR2, DDR3 all double-pump.
It's just that each successive gen allows for higher base clocks.
It's impossible to get DDR to 1200 MHz, hard for DDR2, and easy for DDR3.
a c 376 U Graphics card
March 5, 2010 11:22:41 PM

The bottom line when comparing those 2 cards is that the HD4770 is 5-10% slower than the HD4850 overall. The HD4770's advantage over the HD4850 is that its processor is built using a 40nm process which allows for greater power efficiency. Which you should get depends on how you personally value those 2 aspects and price.
a c 271 U Graphics card
August 3, 2011 9:08:56 AM

This topic has been closed by Mousemonkey
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