Ram - How much performance does Dual Channel add?

[maggotmac]

Hi,

I've got a mid-2009 13" Macbook Pro and am thinking about upgrade the ram as I've found my page outs gets quite excessive and system slows down when working on CAD/Matlab with the rest of my things open (I have a second screen with iTunes/Mail etc running 24/7).

I currently have 2GB and I've found on Crucial that I can get 1 x 4GB of ram for about the same as 2x 2GB of ram. ±£3/4 So upgrading to 4GB or 6GB for the same price.

Does loosing dual-channel have that much of an influence if i'm gaining 2 extra GB's? I'm keeping one eye on upgrading to 8GB in the future but can't afford to at the moment. Also will upgrading, in say, 6 months/1 year to 8GB by adding another 4GB cause any problems so long as I buy from crucial again? I've heard that it is best to buy them in sets so they are identical.

Thanks.

 

[grahamnp]

Mixing RAM is not recommended but not known to cause much problem. You won't get much of a difference at all when running in dual channel. I say go for the 6GB.

 

[dusk007]

Only in applications that use both cores and need to be fed a lot of memory continuously dual channel helps but that is applies to very little things.
Also it may just work with mixed RAM. At least on Desktop Mainboards the days where you really need two equal RAM for dual channel are long past.

 

[maggotmac]

Mixing RAM is not recommended but not known to cause much problem.

So it's not recommended but there are no known problems with it... So why do people recommend not to?

Only in applications that use both cores and need to be fed a lot of memory continuously dual channel helps but that is applies to very little things.

Are there any commercial/popular apps that I might have which would suffer from this?

 

[fibrizo]

So it's not recommended but there are no known problems with it... So why do people recommend not to?



Are there any commercial/popular apps that I might have which would suffer from this?

You don't lose dual channel then.

Dual channel theoretically provides double the memory bandwidth, which would be important in intensive apps, and games, due to the graphics sharing the memory bandwidth. But again these gains are probably not too great.

I do believe that most modern chipsets (ie most since 2004) Allow for flex dual channel. Which means if you have a 4gb and 2 gb stick, the first 2 gb of each stick (ie 4gb) will run in dual channel mode, and the remainder 2gb on the 4gb stick will run in single channel mode.


Intel has pics and details. the flex mode is on the bottom.
http://www.intel.com/support/motherboards/desktop/sb/cs-011965.htm

 

[maggotmac]

Thanks fibrizo,

I think I'm going to go ahead and get the 4GB stick for 6GB total.

 

[grahamnp]

It's not a big deal really. Mixing RAM is supposed to reduce stability (not by much, I'd imagine) but I don't have experience of this and don't understand why so I won't defend this argument. As with all computer parts, when two things run at different speeds, you get the speed of the slowest component so that's another reason.