[Pao|o]

I know the 13" Macbook needs identical RAM modules in pairs but does the Macbook Pro have this requirement as well?

[GoCats]

No. The reason the Macbook needs RAM in pairs is to support the shared video memory. Since the MBP has a dedicated video card with it's own memory, this is not necessary.

[Pao|o]

Thanks So having 1.5GB RAM in a MBP doesnt slow down the machine vs 512MBx2?

[mduell]

Neither requires identical pairs. Both run fine with one stick, two unmatched sticks, or two matched sticks.

You'll receive the best overall performance from two large, matched sticks, as that gives you the maximum memory quantity and bandwidth.

[MacBookProJoE]

i agree with mduell, it is not required to have identical pairs in either laptops. I just recently upgraded to 2 gigs and gave my girlfriend my 512. She now has 768 megs and is running better than before.. but now we have a 256 laying around... damn apple for putting 2 256 instead of one 512. hella weak!!


-JoE

[Bryanmc]

Originally Posted by MacBookProJoE

i agree with mduell, it is not required to have identical pairs in either laptops. I just recently upgraded to 2 gigs and gave my girlfriend my 512. She now has 768 megs and is running better than before.. but now we have a 256 laying around... damn apple for putting 2 256 instead of one 512. hella weak!!


-JoE

When I ordered my MBP you could pay to have a single stick instead of two. Don't know if you can do that with the MacBook or not.

[Cadaver]

I read somewhere that while the Intel chipset in the MacBook Pros supports increased bandwidth with two matched RAM modules, real-world performance doesn't really change, for the reasons noted above (i.e., dedicated graphics chip & VRAM).

[Velocity211]

I have two 1GB chips in my PB but they are different brands, one is apple original and the other one I bought from newegg. Will this affect the performance?

[mduell]

Originally Posted by Velocity211

I have two 1GB chips in my PB but they are different brands, one is apple original and the other one I bought from newegg. Will this affect the performance?

No.

[Tuoder]

Originally Posted by Velocity211

I have two 1GB chips in my PB but they are different brands, one is apple original and the other one I bought from newegg. Will this affect the performance?

I concur with mduell. This would only matter with a crappier (symetric and crappier) implementaion of dual-channel memory.

[cornwallstone]

Certainly, if you're using more than 1GB of memory, a 1GB stick with a 512MB stick will be faster than swapping out to disk with two 512MB sticks. However, if you aren't using more than 1GB, the unmatched pair will cost you about 4% real-world performance on a machine with dedicated graphics, from all the tests I've seen. I agree that most users won't be able to tell the difference, but keep in mind that's about the same real world difference as that between 1.83GHz and 2.0GHz or 2.0GHz and 2.16GHz processors.

According to Intel's datasheet, to get "matched" (symmetric dual-channel) performance with the Intel chipset, only the speed and memory size need to be the same. You don't need the same brand or technology. Read it for yourself here: Mobile Intel 945 Express Chipset Family Datasheet

Page 331

Dual-channel Symmetric Mode

This mode provides maximum performance on real applications. Addresses are between the channels, and the switch happens after each cache line (64-byte boundary). The channel selection address bit is controlled by DCC[10:9]. If a second request sits behind the first, and that request is to an address on the second channel, that request can be sent before data from the first request has returned. Due to this feature, some progress is made even during page conflict scenarios. If two consecutive cache lines are requested, both may be retrieved simultaneously, since they are guaranteed to be on opposite channels. The drawback of Symmetric mode is that the system designer must populate both channels of memory so that they have equal capacity, but the technology and device width may vary from one channel to the other.


Dual-channel Asymmetric

This mode trades performance for system design flexibility. Unlike the previous mode, addresses start in channel A and stay there until the end of the highest rank in channel A, then addresses continue from the bottom of channel B to the top. Real world applications are unlikely to make requests that alternate between addresses that sit on opposite channels with this memory organization, so in most cases, bandwidth will be limited to that of a single channel. The system designer is free to populate or not to populate any rank on either channel, including either degenerate single-channel case.


It's a different story with computers that use the integrated graphics (Mini, MacBook, and some PCs). Matched memory can result in up to 70% faster performance with some applications, in tests I've seen.

Page 353

The entire IGD [Integrated Graphics Controller] is fed with data from its memory controller. The GMCH's graphics performance is directly related to the amount of bandwidth available. If the engines are not receiving data fast enough from the memory controller (e.g., single-channel DDR2 553), the rest of the IGD will also be affected.

[Dr.Michael]

Isn't there anyone here who can do us all a favour and test 2*256 against 1*512? This cannot be found anywhere. As mduell pointed out elsewhere, all available comparisons with matched and unmatched pairs suffer from different memory sizes in the two configurations.

There is a good benchmark tool available from geek patrol. It only lacks graphics benchmarks (which may be the crucial ones). So if someone updated his/her book from 512 (2*256) to 1 gig (2*512) and has Quake or Unreal, please post some results for the MBP and the MB, if possible.