2200 Views 1 2 3 4 Previous Next 54 Replies Latest reply: Jun 3, 2007 4:23 AM by Barry Fisher Go to original post
My two pesos!
The 1.83 17" iMac doesn't really have 512 MB of RAM available for the OS and apps because a minimum of 80 MB is used by the video card. You have even less as the video demand increases, such as when using Photoshop. CS2 will need to use Rosetta as well.
You are kind of wasting money if you put in more RAM than the iMac specs call for because, for instance, the 1.83 GHz 17" model can only address a maximum of 2 GB of physical RAM and the other models can only address a maximum of three GB.
Apple recommends that when you seat mismatched RAM modules, that the larger of the two be seated in the RAM slot closest to the display.
Matched RAM increases the throughput of data from the
RAM to the processor, but I wouldn't be too worried
about it. We're only talking an increase of a few
percent. 2 x 512 MB will be slightly faster than 1 x
1 GB, but 1.5 GB is certainly preferable to 1 GB. The
extra 512 MB will increase your performance more than
using matched pairs ever will.
Actually, in this case, I would recommend you matching the ram. Since you have the intel graphics chip set, you don't have dedicated vram. It has to share ram with system memory. This is one case where having dual channel support does boost graphics performance significantly. So if you upgrade, either upgrade to 1GB or upgrade to 2GB, don't go with 1.5 GB.
I can no longer find apple's white paper on the imac/mac mini which talked about dual channel support for computers with the intel graphics chip. I did find 2 references.
Most of these referencec deal with the mini, but the architecture is the same for any of the macs with the integrated intel graphics chip.
here is the first reference written by Blizzard (creator's of WoW):
After some examination of the Intel-based Mini's specs, it's my opinion that the ideal config for WoW will be to have a minimum of 1GB RAM installed, as a matched pair of DIMMs.
The CPU (either Core Solo or Core Duo) can use up to about 5GB/sec of memory bandwidth maximum; by having matched pairs of DIMMs installed, thhe machine has around 10GB/sec of total memory bandwidth to share between CPU and GPU tasks. At times when the CPU is executing out of its L2 cache (which is fairly large in the Core Solo and Duo), the GPU will have a larger percentage of that RAM throughput available.
A 1024x768 screen, refreshing at 60Hz and 24-bit color depth, will consume about 0.13 GB/second of bandwidth just for the pixel refresh, this is not too big of a deal.
At 5GB/sec, that should be enough fillrate to hit every pixel at 1024x768 res (assuming 24 bit color and 24 bit Z or a total of 6 bytes per pixel) over 1000 times in a second. Oh, but texture fetch bandwidth will eat into that too, so that is a very loose back-of-the-envelope number or "upper bound". Real games have more work to do than just sitting in a loop repeatedly erasing the frame buffer etc; they also tend to hit each pixel in the scene more than once.
(*) assuming the RAM "dual channel" mode is active and the DIMMs are 64-bits wide each, yielding a 128-bit wide memory system at 667MHz peak throughput.
Bottom line is that the new Mini is probably at its best for GPU speed when you have matched DIMMs installed. The base config has matched DIMMs but only 512MB total; we'd recommend 1GB minimum due to the shared RAM configuration.After some examination of the Intel-based Mini's specs, it's my opinion that the ideal config for WoW will be to have a minimum of 1GB RAM installed, as a matched pair of DIMMs.
Note from MacWorld:
Speaking of speed, there’s an important reason why Apple emphasizes (but doesn’t insist) that you should install RAM in pairs in the new Mac mini. It features a dual-channel memory controller—the machine can move double the amount of data through its memory than it could otherwise.
As I said before, the GMA 950 is integrated and doesn’t have its own discrete video RAM, or VRAM. It allocates its own frame buffer memory from the main system memory. Installing RAM in matched pairs can improve your Mac’s overall performance when you’re running software that’s likely to put a toll on the graphics chip.
if I can find the white paper, I'll post the section in it dealing with dual channel support.
Hey, hey! Perhaps someone can answer this -
From the little bit of research I'm able to do on this in the Developer Notes, ALL G5 iMacs and ALL Intel-based iMacs have the combined memory of the DIMMS "configured as a contiguous array of memory."
Yet according to the following Apple Support article it's ONLY the first and second generation G5 iMacs that can benefit from "matching" memory. Benefit of using matching memory modules (RAM)
By process of elimination, and due to the lack of further references to their RAM, G5 iMac iSight models benefit from neither "matching" nor "interleaving."
In ALL the Intel-based iMacs "both SO-DIMMs must be the same size and type for the interleaving function to be used to improve performance."
However, in the above linked Apple Support article the final sentence states: "If you have an iMac G5 (iSight) or an iMac (Early 2006), the configuration of memory is different in your computer and these instructions don't apply."
So, what is the "configuration of memory" in the Intel-based iMacs called, since it's apparently called something other than only a "contiguous array"?
It's not mentioned in either:
iMac (Early 2006), iMac (Mid 2006), iMac (17-inch Late 2006 CD): Memory Specifications
iMac (Late 2006): Memory Specifications
Without knowing the answer to this, I must admit I'm LOST:(
Message was edited by: myhighway
One thing for sure IMO, from now on we each need to well establish just which iMac model we are suggesting advice about with regard to RAM, because from the info in these referenced articles, although, with the exception of a 2 GB module, one size fits all, but won't necessarily be used the same way from model to model.
Might avoid any future dust-ups.
Sorry, I don't mean to confuse things further, but I only just noticed that in the three Developer Notes, the extra sentence that is in the late 2006 iMacs' "Memory" sections which is absent from the early 2006 "Memory" section:
"Additional RAM must be installed in pairs of equal sizes."
Not that it makes any sense to me, just what I'm reading:
"The computer provides two RAM slots that accommodate 200-pin DDR2 SDRAM SO-DIMMs up to 1.25” in height. The SO-DIMMs must be DDR2 PC2-5300-compliant and must be unbuffered, unregistered, 8-byte, nonparity, and non-ECC."
Late 2006 with ComboDrive:
"The iMac provides two RAM slots that accommodate 200-pin DDR2 SDRAM SO-DIMMs up to 1.25” in height. The SO-DIMMs must be DDR2 PC2-5300-compliant and must be unbuffered, unregistered, 8-byte, nonparity, and non-ECC. The iMac ships with two 256 MB DDR2 SDRAM SO-DIMM in two RAM slots for a total of 512 MB. Maximum memory is 2 GB. Additional RAM must be installed in pairs of equal sizes."
Late 2006 with SuperDrive:
"The iMac provides two RAM slots that accommodate 200-pin DDR2 SDRAM SO-DIMMs up to 1.25” in height. The SO-DIMMs must be DDR2 PC2-5300-compliant and must be unbuffered, unregistered, 8-byte, nonparity, and non-ECC. The iMac ships with two 512 MB DDR2 SDRAM SO-DIMMs for a total of 1 GB memory. Maximum memory capacity is 3 GB. Additional RAM must be installed in pairs of equal sizes."
Perhaps this has something to do with the fact the Apple Store has only been offering its iMac C2D memory in pairs, yet it is STILL offering to sell single RAM modules for the early 2006 (Core Duo) models???
Message was edited by: myhighway
As the poster of the original question, I'm certain now that the answer appears not as simple as I first assumed. I still would like a clear summary gleaned from all of the responses . . . for myself in particular and for others who may be generally confused. For my specific model - the base iMac Intel Core 2 Duo 17" 1.83 GHz (purchased this past month), would it be an acceptable option to add a 1 Gig module to my factory installed 512 for an unmatched total of 1.5 gigs . . . or would an additional matching 512 be the safest and most efficient way to upgrade my memory? Thanks for all the responses that my "simple" question has generated . . .
Thanks for clearing that up . . . I was under the wrong assumption all along that I had a factory installed 512 module and that the other slot was empty. So then with either of your suggestions it seems I have to disgard the 2 256MB modules. That seems wasteful to me . . . that to upgrade my memory I have to throw away the memory that was factory installed and that I paid for. Thanks again for being patient with all of the advice . . . and hopefully this discussion may benefit others with similar concerns.
From the perspective of trying to learn from Apple's Support articles, a difficult problem to deal with can occur when Apple updates the info in an article. Yes, at the bottom they do update the date of the article, but there is no note of the previous date. For those of us who bookmark these articles for ease of providing timely responses to other members' questions, a newly revised article is pulled up just the same as if it hadn't changed.
My memory is still fairly good, but not good enough to remember the previous date on the article, and certainly not good enough to recall the specific wording of the article. Therefore, even when I completely re-read an article after it's been updated, it's not always easy at all to make the connection that - "oh, look, this is different than it used to be" - I sure wish I was able to do that:))
To avoid another case of waste developing, you might want to skip straight on up to the 2 x 1GB modules setup. Since two of the three current MacBook Pro machines are currently being offered with 2GB of base memory (base, not optional), I think that's a pretty good hint of where things are headed for the rest of us, especially after Apple TV but still with Leopard, the iPhone, and who knows WHAT all in the works!!! If only we could clone Steve:))