Topic Title: Is CAS timing or memory speed most important for APU graphics?
Topic Summary: Memory speed
Created On: 02/23/2014 12:31 AM
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 02/22/2014 10:51 PM
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AMDforMe
Overclocker

Posts: 675
Joined: 09/08/2013

Actually RAM timings on DDR3 running at 1333 MHz. or higher make very little difference. The reason for this is that at 1333 MHz. or higher DDR3 doesn't impose a bottleneck to the system. A system using an APU can benefit from higher frequency RAM if the APU actually supports it because the GPU section can use the added bandwidth.

In addition as RAM frequency increases one clock cycle becomes less in real time so CAS9 1333 MHz. RAM can have very similar real time as CAS11 1600 RAM, i.e. 13.5ns vs. 13.75ns respectively. 

http://en.wikipedia.org/wiki/DDR3_SDRAM

You are not going to see major improvement by going from 1333 MHz. to 1600 MHz. but you will definitely see some. Mixing of RAM can be a crapshoot but you can buy another 4GB 1600 MHz. SO-DIMM for ~40.  You could also buy 2x 2GB 1600 MHz. SO-DIMM kit for ~$50. The 2x 4GB 1600 MHz. kits are >$75.

Looks like the forum has some technical issue placing replies above the OP's question??? Very strange!



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Technical ignorance is NOT a destiny it is a choice. Do your homework so that you can make technically informed decisions and not be duped by advertising hype or mis-information stated as fact when its not.


 



Edited: 02/23/2014 at 12:17 PM by AMDforMe
 02/23/2014 12:31 AM
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Peon

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Joined: 02/23/2014

So I got a laptop a couple weeks ago that has an A8 4500m and a Radeon 7640g GPU.

It came with 1 SoDimm 4 Gigs running at 1600 mhz.

I know dual channel is very important for GPUs that share system memory, so even though it is slower I put in another SoDimm I had laying around running at 1333 mhz.

Sure enough even tho my memory speed went down with dual channel and the lower CAS I got a NICE boost in performance.

So my question is this.

Right now I am running at 1333 mhz CAS9. The 1600mhz stick this laptop came with is rated for CAS11 @ 1600 mhz.

I was thinking of getting another 1600 mhz stick to replace the 1333mhz stick I am using........but I am worried if they both are running @ CAS11 vs CAS9 then the performance difference will be negligable.

So then I will be in the position where instead of having to buy 1 more stick I might need to buy 2 both at at least CAS9.

How much of a difference does CAS latency make vs the mhz rating?

Thank you

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