Question on DDR2 RAM

[xxcool]

I had asked this question in another thread before so please don't flame me for being redundant, I'm really just trying to get some straight answers and solicit opinions from people.

Anyway, I heard and read the the DDR2 RAM used in the MBP works best when installed in pairs to get the full 128 bit access, so if I opt for the 3gb RAM option, will I lose that benefit?

I spoke to an Apple sales rep about this and he put me on hold to check with a tech support. He came back with some vague answer saying that I won't lose the benefit. "Benefit of what?" I tried to press him to answer my question but I got the sense that he really didn't know what he was talking about.

So does anyone here have a definitive answer? If this is indeed the case, isn't that poor engineering decision to allow only up to 3 gb of RAM? I guess unless you can install 2x1.5bg.

Will going for 3gb of RAM still a wiser choice even though you wipe out the benefit of 128 bit access?

Thanks in advance for any comments.

 

[Silentwave]

If you need 3GB RAM (getting lots of pageouts with 2GB) then get 3GB.
You lose some part of the RAM bandwidth, but in the case of the MBP it is minor- it has more effect where integrated graphics are involved (like the MB) or so I'm told.
It's a chipset limitation to 3GB i'm afraid.

 

[WildCowboy]

Yes, you will lose the speed benefit of matched pairs. However, the benefit is very small and is trumped by the fact that you will have more total RAM, which should give you faster performance.

However, it also depends on how much RAM you routinely use. If you never use more than 2 GB of RAM, you might see better performance from a matched 2 GB set. But the general rule of thumb is that the primary consideration is the amount of RAM, with the matched RAM being secondary.

This is particularly true in machines with separate graphics cards to handle display duties. Matched RAM seems to have a bigger effect on shared-RAM machines like the MacBook and the mini. But the MacBook Pro doesn't see much benefit (6-8% anecdotally) in matching the RAM...you'll usually be better off to go straight to 3 GB if you need it. It's pricey though.

 

[gr8tfly]

hi,

According to the Apple Developer Notes on the MacBook Pros, there is no restriction as to matching capacity. The Mac Pro, however, does, but I don't have the specifics handy. Here's the "RAM Expansion" dev. note link: http://developer.apple.com/documentation/HardwareDrivers/Conceptual/HWTech_RAM/index.html#//apple_ref/doc/uid/TP40003031

The reason for the 3GB limitation is how some of the internal I/O address space is mapped - it conflicts with portions above 3GB. Perhaps in a future version of the main board, it will be relocated.

I'm going with the stock 2GB for now (hoping to get the machine this week, but so far, none of the 17" MBP C2Ds have shipped). I figure that in 6mo, I can most likely pick up a 2GB SODIMM for a lot less than the ~$450 Apple gets (and, a WHOLE lot less than OWC - they're over $600).

 

[Eidorian]

"Intel® Flex Memory Technology" allows for dual channel access on chips that aren't the same size.

 

[Demon Hunter]

I had asked this question in another thread before so please don't flame me for being redundant, I'm really just trying to get some straight answers and solicit opinions from people.

Anyway, I heard and read the the DDR2 RAM used in the MBP works best when installed in pairs to get the full 128 bit access, so if I opt for the 3gb RAM option, will I lose that benefit?

I spoke to an Apple sales rep about this and he put me on hold to check with a tech support. He came back with some vague answer saying that I won't lose the benefit. "Benefit of what?" I tried to press him to answer my question but I got the sense that he really didn't know what he was talking about.

So does anyone here have a definitive answer? If this is indeed the case, isn't that poor engineering decision to allow only up to 3 gb of RAM? I guess unless you can install 2x1.5bg.

Will going for 3gb of RAM still a wiser choice even though you wipe out the benefit of 128 bit access?

Thanks in advance for any comments.

For more information see this thread.

 

[Eidorian]

For more information see this thread.

A better link.

 

[WildCowboy]

Dang...I'm so out-of-date.