[X4U] RAM Memory - What's the max?

[Stroller]

On 20 Jul 2007, at 15:27, Robert A. Virzi wrote:

> More memory is good.  I have heard conflicting reports on max  
> memory for macbook pros.  I have a 2 Ghz intel core duo MBP with 2  
> gig of RAM.  I'd like to add more, especially to help with running  
> Parallels.  I've heard:
>
> 2 gig RAM is the max
>
> 3 gig (1Gb and 2Gb strip) will work (Apple store)
>
> 4 gig (2 2Gb strips) see http://www.newegg.com/Product/Product.aspx? 
> Item=N82E16820146684
>
> Does anyone have experience in going over the original 2 GB RAM  
> limit on this machine?

I was surprised to read the Apple Store recommending 3gig, but it  
appears they are correct:
   http://docs.info.apple.com/article.html?artnum=304662
   http://docs.info.apple.com/article.html?artnum=303491

Normally on modern PCs (Core & Core2 Duos, some Pentium 4s & AMDs but  
not sure which models) it's preferred to keep both sticks of RAM the  
same size (usually a "matched pair" of the specification is used) in  
order to allow "dual-channel" access. This basically means that half  
of each byte is stored in each stick of RAM which allows for faster  
memory access than waiting to get the whole byte from a single stick.

Unmatched pairs don't allow the RAM to operate in dual-channel mode  
and from reading those articles I think 2 x 2gig sticks in a MacBook  
Pro wouldn't either.

Realistically, however, the speed difference is negligible for most  
applications - all the discussions I've read about this have been on  
a video-playback mailing list. User observations there seem to  
suggest you can only tell when using the machine for 1920 x 1080 hi- 
def video - which is quite demanding - when the machine is at its  
limits anyway. EG: 1 x 1gig stick (in single-channel mode) might  
stutter during playback whereas 2 x 512meg sticks (dual-channel) or 1  
x 2gig (single-channel) would not. Note that the 1 x 1gig RAM might  
not cause a faster processor to stutter.

 From the Apple articles you'd benefit from replacing one of your  
1gig sticks with a 2gig, providing your apps are using it. Clearly  
this would work and the only reason not to is if you're concerned  
about the cost - to estimate if the investment would be worthwhile  
the best thing to do is open Activity Monitor & watch how much free  
memory you have. Memory is shown by selecting the 2nd tab, 2/3 down  
the page, and is shown in green. Check back in that window  
periodically and when your 2gig Mac is out of free memory then that  
is when you'll benefit (my some inestimable amount) from the extra  
RAM. If you're running Parallels (and Safari and Mail and Word  
and ...) and there's still green in the pie-chart then the expense of  
extra RAM would be of no benefit. Of my new 2gig RAM nearly half is  
still unused and I've been using my machine moderately for a number  
of hours today.

I make these remarks because I'd personally find it cost-prohibitive  
to throw away 1gig of RAM to increase memory by only 50% - whereas I  
might be prepared to dispose of both sticks were I able to double the  
RAM (and I felt the need). It's not clear from Apple's site whether  
the 3gig maximum is a limitation of 10.4 or of the MacBook itself - I  
guess since a G5 or (presumably) MacPro can use 4gig that the  
MacBookPro is the cause and that there's no chance that later o/s  
updates will allow use of 4gig in it.

Stroller