Does IGP slow down CPU memory access?

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Does IGP slow down CPU memory access?

Postposted on Tue Jul 31, 2012 9:01 am

Since IGP shares main memory with CPU, does it slow down CPU memory access? BTW I only use light 2D graphics to display real time financial market data chart. I think for heavy duty graphics application, that will become an issue.
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Re: Does IGP slow down CPU memory access?

Postposted on Tue Jul 31, 2012 9:26 am

In theory sure, but it shouldn't impact any common usage scenario.
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Re: Does IGP slow down CPU memory access?

Postposted on Tue Jul 31, 2012 9:56 am

The thing to remember is that its going to be shared memory, and most IGP's memory access can be limited in quantity. That being said, the IGP doesn't care a bit when you are loading a large spreadsheet or what-not. This requires no shaders and generally won't even have a measurable impact on your CPU. If you are worried about it, set your IGP memory down to 128 MB.
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Re: Does IGP slow down CPU memory access?

Postposted on Tue Jul 31, 2012 10:12 am

There are tons of optimizations, cached writes, bulk reads and writes to reduce the impact... but yes when its all done, the IGP *IS* using #x64 memory paths to the main memory and is sharing the memory buss reducing the amount of bandwidth available to the cpu.
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Re: Does IGP slow down CPU memory access?

Postposted on Tue Jul 31, 2012 10:52 am

In general, yes. You will see a slight reduction in memory performance when using an IGP, due to the memory bandwidth being used to refresh the display. For a given resolution, the impact on memory performance has gone down over time due to the steady increase in overall available memory bandwidth.

Server motherboards typically have a dedicated frame buffer for their onboard graphics, and are therefore unaffected by this issue.

A (very) small number of AMD desktop motherboards implement a feature called "SidePort" which is essentially a dedicated IGP frame buffer. All the ones I've seen have been 128MB... if you need more than 128MB VRAM it starts using system RAM just like a normal IGP.
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Re: Does IGP slow down CPU memory access?

Postposted on Thu Aug 02, 2012 7:11 pm

I can remember when using the IGP (usually SiS) on early 66MHz FSB K6 and P2 boards nearly cut memory bandwidth in half--and made 2D redraws noticeably slower on the K6 systems. We don't have it nearly as bad today. :)
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Re: Does IGP slow down CPU memory access?

Postposted on Thu Aug 02, 2012 9:04 pm

IIRC you get a lot more benefit out of dual-channel RAM if you're using IGP.
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