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Which is more important, data rate or CAS latency, when choosing RAM?

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April 3, 2014 6:25:15 AM

I'm upgrading from 6gb to 8gb of RAM, and have been comparing stats online.

I've found two 4gb modules of PC3-12800 with a CL of 11, and two other 4gb modules of PC3-10600 with a CL of 9.

So, is data rate or CAS latency more important?
April 3, 2014 6:31:49 AM

Hi, first question- in what context?

If you're building a system around an AMD APU (laptop OR desktop) then correct ram settings is essential to get the most out of it.

If however you're machine has a dedicated graphics card then the specification of the memory makes very little difference in overall perforamance.

The other key question- if you're upgrading from 6gb to 8gb I'm assuming you're keeping a 4gb module already and adding a second? In that case you need to match you're new 4gb module to the old one. The machine will only be able to run them both at the speed of the slowest anyway, and ideally ram should always be matched. If you put dissimilar ram modules together in the machine it can cause all sorts of problems and may not even boot up...
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April 3, 2014 7:23:15 AM

cdrkf said:
Hi, first question- in what context?

If you're building a system around an AMD APU (laptop OR desktop) then correct ram settings is essential to get the most out of it.

If however you're machine has a dedicated graphics card then the specification of the memory makes very little difference in overall perforamance.

The other key question- if you're upgrading from 6gb to 8gb I'm assuming you're keeping a 4gb module already and adding a second? In that case you need to match you're new 4gb module to the old one. The machine will only be able to run them both at the speed of the slowest anyway, and ideally ram should always be matched. If you put dissimilar ram modules together in the machine it can cause all sorts of problems and may not even boot up...


Hi, thanks for the quick response.

It's a laptop with a integrated Intel HD Graphics 3000 card. And the RAM limit is 8GB.

Yeah I already have a 4GB card, it's a PC3-12800 with a CAS latency of 9. The 2GB card is a PC3-12800, also with a CAS latency of 9.

Obviously I'd like to get a card which is exactly the same as the 4GB one I already have, but I can't find one with a CL of 9 (all other specs match up though).

So the problem is that I can get 1 new 4GB card, but the CAS latencies won't match. Alternatively, i could get two new 4gb cards, both with exactly the same specs, but they'll cost twice as much.
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April 3, 2014 7:30:24 AM

matb said:
cdrkf said:
Hi, first question- in what context?

If you're building a system around an AMD APU (laptop OR desktop) then correct ram settings is essential to get the most out of it.

If however you're machine has a dedicated graphics card then the specification of the memory makes very little difference in overall perforamance.

The other key question- if you're upgrading from 6gb to 8gb I'm assuming you're keeping a 4gb module already and adding a second? In that case you need to match you're new 4gb module to the old one. The machine will only be able to run them both at the speed of the slowest anyway, and ideally ram should always be matched. If you put dissimilar ram modules together in the machine it can cause all sorts of problems and may not even boot up...


Hi, thanks for the quick response.

It's a laptop with a integrated Intel HD Graphics 3000 card. And the RAM limit is 8GB.

Yeah I already have a 4GB card, it's a PC3-12800 with a CAS latency of 9. The 2GB card is a PC3-12800, also with a CAS latency of 9.

Obviously I'd like to get a card which is exactly the same as the 4GB one I already have, but I can't find one with a CL of 9 (all other specs match up though).

So the problem is that I can get 1 new 4GB card, but the CAS latencies won't match. Alternatively, i could get two new 4gb cards, both with exactly the same specs, but they'll cost twice as much.


Yeah you really need to get the same.

I've done a little digging and you can get a 4gb, PC3-12800 module with cl-9 if you look around, an example:
http://www.ebuyer.com/370058-corsair-4gb-ddr3-1600mhz-v...

Another good source for specific ram is Kingston Memory:
http://www.kingston.com/en/memory/upgrades?ktc_campaign...

Or Crucial Memory:
http://www.crucial.com/uk/index.aspx?gclid=CMrb0uDDxL0C...

Both should be able to provide something that matches if you can't find it anywhere else (although it might cost a little more).

By the way, what is your reason for upping the ram? Given the specifications of your laptop I'm not sure it will provide much benefit unless your running some software that's using all your current 6gb?
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April 3, 2014 8:12:45 AM

Thanks for the links

I've got 3D modeling software/2D vector-drawing software which run slowly and sometimes crash when they're doing a lot of work.

Is there much of a difference between a CAS latency of 9 and one of 11? I know the 9 will function better, but is there a real difference between the two?
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April 3, 2014 8:22:54 AM

matb said:
Thanks for the links

I've got 3D modeling software/2D vector-drawing software which run slowly and sometimes crash when they're doing a lot of work.

Is there much of a difference between a CAS latency of 9 and one of 11? I know the 9 will function better, but is there a real difference between the two?


In terms of performance I don't think you'd notice a difference between CL-9 and CL-11 (it really is minimal). The only thing that concerns me is *if* the laptop will accept a stick of CL-9 memory and another that's CL-11. It might work fine, however it could lead to some annoying problems / instability of the system if not.

I do allot of 3-D design work myself- unfortunately I think your issue here is quite possibly the performance of that integrated HD 3000 gpu.

If you want a cheap laptop for 3-D work I'd recommend looking a an AMD A-Series based machine (at least an A8) as they incorporate a Radeon GPU which is faster and better supported by this type of software.
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April 3, 2014 2:04:35 PM

I had feared the GPU would be the source of the problem - I've tweaked some of the settings for the GPU and the 3D modeling software does work more smoothly.

I think the increased RAM and RAM speed will probably improve the laptop as a whole, so I'm still going ahead and upgrading.

I've had a look around the web and it appears to be that the laptop/pc doesn't need a specific CL number to use the card. The guides on choosing ram don't talk about ensuring the CL number is constant, and the manufacturers page on the laptop also don't make it apparent that any RAM must have the right CL number.

Thanks for the help,
Matt
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