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Ram Dilemma
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AlbanianGenome
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May 23, 2008, 08:33 PM
 
I just bought a refurbished 2.16ghz Snow White iMac. I have been debating on increasing the ram from the standard 1 gig it comes with, but when i look for ram supported it says it can only support 3 gigs of ram. Enter the dilemma. I have always heard that not matching ram sticks is a no no in memory world, supposedly because then the dual channel memory support for increased performance can not be taken advantage of. On the other hand I hear that this iMac can't even support that and its a function of the motherboard, if it can support that or not. I could install 2 2 gig sticks for a total of 4 gigs but this computer is only going to recognize 3. Or I could just buy a 2 gig stick and total it to 3 gigs like apple says its supported to do. Not sure if one solution is better than another, and if having non matching sticks of ram confuses the computer or not. Any help or advice on the matter would be welcomed, thank you in advance.
     
mduell
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May 23, 2008, 08:58 PM
 
Unless your applications are very sensitive to memory bandwidth (most aren't), unmatched memory is fine in the iMacs.

2GB SO-DIMM DDR2 667 and 1GB SO-DIMM DDR2 667 gets you there for $65 shipped.
     
Simon
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May 24, 2008, 01:48 AM
 
Originally Posted by AlbanianGenome View Post
I just bought a refurbished 2.16ghz Snow White iMac. I have been debating on increasing the ram from the standard 1 gig it comes with, but when i look for ram supported it says it can only support 3 gigs of ram. Enter the dilemma. I have always heard that not matching ram sticks is a no no in memory world, supposedly because then the dual channel memory support for increased performance can not be taken advantage of. On the other hand I hear that this iMac can't even support that and its a function of the motherboard...
Every modern Mac supports dual channel memory.

The thing is that it doesn't lead to a performance increase unless you do very specific things on certain hardware. The most prominent example being 3D accelerated graphics on a Mac w/o dedicated VRAM (for example some games on a Mm, MB, or MBA). In such a situation you actually see performance gains from the increased memory bandwidth.

Since you have dedicated VRAM on your iMac that will not be an issue. And if you had been developing an app that relies highly on mem bandwidth, you'd know it. So IOW forget pairing and get 3 GB. Especially now that RAM's so cheap.
     
AlbanianGenome  (op)
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May 24, 2008, 04:12 PM
 
i thought imacs have non-integrated graphics cards? The macbook for example has integrated graphics on board. So when you say dedicated, are you referring to non-integrated? As far as ram is concerned as well, the cas latency of ram matters? Most of the 2 gig sticks I am seeing are 5, but a few are 3.
     
mduell
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May 24, 2008, 05:29 PM
 
Originally Posted by AlbanianGenome View Post
i thought imacs have non-integrated graphics cards? The macbook for example has integrated graphics on board. So when you say dedicated, are you referring to non-integrated? As far as ram is concerned as well, the cas latency of ram matters? Most of the 2 gig sticks I am seeing are 5, but a few are 3.
There are four terms to be aware of -
Discrete GPU: the graphics processing chip is seperate from the chipset (sometimes on a card, sometimes soldered to the logic board)
Integrated GPU: the graphics processing chip is integrated into the computer's chipset
Dedicated VRAM: the video memory is a seperate group of chips on the graphics card or logic board
Shared VRAM: part of the main system memory is used for video memory
You can mix and match discrete/integrated GPUs with dedicated/shared VRAM, but so far Apple has only used the discrete/dedicated and integrated/shared combinations. Discrete/dedicated is generally higher performance, higher heat, and higher cost while integrated/shared is lower performance, lower heat, and lower cost. Features (OpenGL version and option features) and screen resolutions are independent of the graphics system architecture.

Most of the iMacs has discrete GPUs and dedicated VRAM, but some have integrated GPUs and shared VRAM. Graphics systems are particularly sensitive to memory bandwidth, so when you have shared VRAM it's important to use dual channel memory. Unless your applications are sensitive to memory bandwith, it's fine to use different size memory modules if your computer has dedicated VRAM.

CAS (and the other latency figures... tRAS, etc) does matter for applications that are sensitive to memory latency, but Apple's computers aren't configured to take advantage of memory that is capable of the more aggressive timings, so you may as well save a few bucks and buy the higher latency stuff.
     
Simon
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May 24, 2008, 05:54 PM
 
Originally Posted by AlbanianGenome View Post
i thought imacs have non-integrated graphics cards?
All current iMacs do. And your 2.16 Ghz iMac does as well.

The macbook for example has integrated graphics on board. So when you say dedicated, are you referring to non-integrated?
No. Dedicated is the ley word here. Dedicated as in dedicated video memory. I'm referring to the fact that your iMac has dedicated VRAM and doesn't have to use RAM as video memory - most importantly the GPU not having to fetch things in memory through the memory interface bus. Instead your GPU has its own VRAM and a dedicated bus to communicate with it. And hence you are almost certainly not going to profit from higher memory bandwidth due to dual-channeling.

As I already said, just get 3 GB and enjoy.
     
AlbanianGenome  (op)
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May 24, 2008, 09:41 PM
 
thank you guys for the helpful feedback, I am looking at 2 gig sticks now, I opened up my iMac and saw that its using a 1 gig Hynix stick saying 555 on part of the readout, so I am taking that as its using cas of 5. If you guys were going to buy a 2 gig stick to work with that module would you rather go Kingston,Crucial, Datamem, Corsair, or a cheaper unit as long as it has a lifetime warranty?
     
mduell
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May 24, 2008, 11:15 PM
 
Crucial if you don't mind the price, Transcend if you're a starving college student.
     
AlbanianGenome  (op)
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May 24, 2008, 11:22 PM
 
lol, I think Crucial sounds good to me THanks again for the help mduell, that was a very insightful post about the terminology. I have a GeForce 7600GT 256meg graphic card in this iMac of mine, so since its not integrated VRAM, I will be fine with a 2 and a 1 gig stock of crucial memory Now if I only had a decent internet connection
     
mduell
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May 25, 2008, 01:07 AM
 
The 7600GT in the white iMacs is actually on a separate proprietary card... in theory you could upgrade it, but no one has made a card to upgrade to.
     
AlbanianGenome  (op)
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May 25, 2008, 02:58 AM
 
it is a pretty sweet card to begin with, couldnt imagine what i would upgrade it to considering it does battle with the brand new radeon 2600 pro with no sweat. mduell, would you buy a 2 gig and 1 gig stick of the same manufacturer, or would you just keep the Hynix 1 gig stick in the machine and throw any brand 2 gig in to match up with it?
     
mduell
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May 25, 2008, 11:06 AM
 
Originally Posted by AlbanianGenome View Post
it is a pretty sweet card to begin with, couldnt imagine what i would upgrade it to considering it does battle with the brand new radeon 2600 pro with no sweat. mduell, would you buy a 2 gig and 1 gig stick of the same manufacturer, or would you just keep the Hynix 1 gig stick in the machine and throw any brand 2 gig in to match up with it?
No reason to throw away the gig you already own; mixing manufacturers is fine.

I don't know that's really a fair comparison, given what a disaster the Radeon HD 2000 series was... the GeForce 8800 or Radeon HD 3600 series would both be compelling upgrades if available.
     
Chinasaur
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May 28, 2008, 08:17 PM
 
Originally Posted by AlbanianGenome View Post
...or would you just keep the Hynix 1 gig stick in the machine and throw any brand 2 gig in to match up with it?
You sure it has a 1GB stick vs two 512MB sticks?
iMac - Late 2015 iMac, 32GB RAM
MacBook - 2010 MacBook, 1TB SSD, 16GB RAM
     
Simon
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May 29, 2008, 03:01 AM
 
Originally Posted by Chinasaur View Post
You sure it has a 1GB stick vs two 512MB sticks?
That is indeed somewhat surprising since the default configurations shipped with 2x512 MB. But Apple sometimes does configure Macs slightly differently when they sell them directly to EDU or business.
     
AlbanianGenome  (op)
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May 31, 2008, 05:27 AM
 
yes i am sure, I was quite surprised as well, but it was a refurb, so not sure of they do that themselves, or possibly the user who bought this machine requested that upon original purchase. Does this surprise you guys?
     
AlbanianGenome  (op)
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May 31, 2008, 05:28 AM
 
oh and to finish up, I decided to get 2 2gig sticks from Crucial, because I sleep better at night knowing my ram sticks match up, lol. There was also that test done by OWC showing that 2 2gig sticks was actually faster than using a 2 and a 1 gig in this 2.16ghz Intel Core 2 Duo 24" iMac that I am using. Take a look for yourself..Performance testing of Apple iMac Core Duo, Core 2 Duo, and Core 2 Extreme Models with various Memory configurationsOtherWorldComputing.com
     
Simon
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May 31, 2008, 07:25 AM
 
The "measured" differences are on the percent level. The benchmarks give no error margin, but these differences are surely within them. You won't get better performance. But if it makes you sleep better at night, I guess it was the right decision.
     
   
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