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RAM and speed increase?

It is often said that adding more RAM to a computer will increase its speed. I understand how this can be true if the computer has too little RAM but that never seems to be mentioned.

My question is, how could adding RAM increase my MacBook's speed if, due to the applications I run, there is always 1/5 or more of the existing RAM available as is displayed in Activity Monitor?

2GHz Macbook Core 2 Duo, Mac OS X (10.4.10), 7200 RPM 200GB Hitachi drive

Posted on Oct 27, 2008 4:16 AM

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12 replies

Oct 27, 2008 10:04 AM in response to Len D

Thanks for the response but I am still not quite clear...

If you open Activity Monitor and click on the Disk Usage tab isn't the swap file included in the blue colored portion of the pie chart? I would think that if there is any green at all ( Free space) then you are not interfering with swap file storage space, unless the swap file uses the green area.

If you click the System Memory tab of Activity Monitor my assumption is that the swap file is in the yellow piece of the pie. Or, is the swap file not shown anywhere on the chart, thus making it difficult to know if there is room enough for it to work unimpeded in the event that there is very little green left?

Oct 27, 2008 12:20 PM in response to Gregory Mcintire

Having 1/5th of your RAM available does not mean that adding more memory will not improve your performance. Most modern operating systems will always try to keep a portion of your RAM free for the most efficient operation of your system. What increasing your installed RAM does is allow more data to be retained in RAM. For example... if you have 1GB of RAM and you see that you typically have 1/5th of your RAM available... and you upgrade to 2GB of RAM, you will likely see an increased amount of RAM used. What you are doing by installing more RAM is giving the system a little more breathing room before it needs to cache data to your hard drive. The more RAM you have, the more data will be retained. The system will always keep a chunk of RAM free however... So, as I had mentioned, just because you have 1/5th available now, that does not mean that you won't see an improvement by installing more RAM.

Oct 27, 2008 1:01 PM in response to Gregory Mcintire

Well, the disk usage tab isn't really helpful in determining swap file usage. It is just showing you how much of your hard drive is currently used up (blue), and how much is free (green). The swap file would be accounted for in the blue area though.

In the system memory tab, the pie chart shows you how your RAM is split up between the "active", "inactive", "wired", and "free" states. Those states only pertain to your RAM and has nothing to do with your swap file. If you add up the active, inactive, and wired values (reg + blue + yellow), you will see how much physical RAM is in use. The green is free RAM. The VM size, I believe, is how large the swap file currently is. The best indicator of how often you are using the swap file is the page in/out values. If those are high, then you would benefit from additional RAM.

Oct 27, 2008 3:35 PM in response to Len D

Len D wrote:
Well, the disk usage tab isn't really helpful in determining swap file usage. It is just showing you how much of your hard drive is currently used up (blue), and how much is free (green). The swap file would be accounted for in the blue area though.

In the system memory tab, the pie chart shows you how your RAM is split up between the "active", "inactive", "wired", and "free" states. Those states only pertain to your RAM and has nothing to do with your swap file. If you add up the active, inactive, and wired values (reg + blue + yellow), you will see how much physical RAM is in use. The green is free RAM. The VM size, I believe, is how large the swap file currently is. The best indicator of how often you are using the swap file is the page in/out values. If those are high, then you would benefit from additional RAM.


Virtual memory is often poorly understood. If you see 4GB devoted to an active process in VM, that doesn't necessarily mean it uses 4GB with part of it as swap space in hard drive space. Part of it is a programming efficiency trick to make the program think that it has (let's say) a 4GB space all to itself, but that doesn't necessarily mean 4 GB is being used for that program. It's likely a smaller space that's mapped to the program space via "dynamic address translation". That's not to say that it can't be swapping to disk to some degree, but that's not generally very good from a performance standpoint.

http://en.wikipedia.org/wiki/Virtual_memory

I'm not that well versed on this, but apparently when it does heavily swap data from drive to memory, it's called "thrashing".

Oct 27, 2008 5:10 PM in response to Gregory Mcintire

I already have 2GB RAM and after a fresh boot it is a long time before there are any page outs. It remains at 0 for a day or more at seems.

So am I right to assume that getting 3GB would not give me any noticeable speed increase. The reason I say 3GB is that my MacBook is a 2006 model and will not address 4GB.

There are two ways to put 3GB in it though. One way is to use a 2GB module and a 1GB module. The other way is to use two 2GB modules. The advantage of this, as I understand it, is that Apple strongly recommends that you use two balanced RAM modules and two 2GB cards would be that where a 1GB and a 2GB would not.

So, what is the consensus?

Oct 27, 2008 5:53 PM in response to Gregory Mcintire

Gregory Mcintire wrote:
I already have 2GB RAM and after a fresh boot it is a long time before there are any page outs. It remains at 0 for a day or more at seems.

So am I right to assume that getting 3GB would not give me any noticeable speed increase. The reason I say 3GB is that my MacBook is a 2006 model and will not address 4GB.


It depends on what you're doing. If you've got a lot of open, memory-hungry applications, more memory is going to help. Always.

There are two ways to put 3GB in it though. One way is to use a 2GB module and a 1GB module. The other way is to use two 2GB modules. The advantage of this, as I understand it, is that Apple strongly recommends that you use two balanced RAM modules and two 2GB cards would be that where a 1GB and a 2GB would not.


The whole thing about matched memory sizes is way overblown. The advantage is marginal. Intel calls it symmetric interleaving, and that's just a fancy way of saying there's a tiny head start when switching from one module to the other. You still get what they call "asymmetric interleaving" up to the size of the smaller module if unmatched in size. I've looked into it, and I'm thinking that a single 2GB module might even be better than 2x1GB. This isn't like other memory controllers where matched pairs effectively act to double the memory bandwidth.

So, what is the consensus?


Read this:

http://eshop.macsales.com/Reviews/MacBook/Testing/Memory_Benchmarks

Their consensus for most memory-hungry applications was that 3GB (1GB+2GB) always completed tasks faster than a matched 2x1GB pair.

They had some funky results with their graphics tests, but those results were barely any different.

Oct 27, 2008 7:53 PM in response to y_p_w

Thanks for the input.

I clicked on the OWC link and from there clicked on the 2006 MacBook tests (what I have) and it turns out that on some of the tests 2GB was a bit faster than 3GB. Most of the tests showed 3GB better. But for the 3GB test they used a 2GB + 1GB card instead of two 2GB cards.

The thing is, I ordered two matched 2GB cards today and then only a short time later I read on their site that my 2006 MacBook would only use a total of 3GB. I emailed them to cancel the order but they said it was too late, it had already shipped. I could send it back once I get it though.

But I am going to be so tempted to install it and try it just to see. If I do that then I can't send it back so what a conundrum I have put myself in!

Again, thanks to all of you for the input. It is much appreciated.

Oct 27, 2008 8:35 PM in response to Gregory Mcintire

A little searching turned up this thread:
http://discussions.apple.com/thread.jspa?threadID=1702392&tstart=0

It turns out that the 06 core 2 duo will recognize up to 4GB but only use 3GB if it is a 2+1GB configuration (obvious enough) but it will use 3.2GB if it is a 2+2GB configuration. It should also have very slightly faster video performance with the matched 2+2.

I just put in a 7200RPM Hitachi HD and it did improve performance. I will likely install the 4GB I ordered when it arrives. I guess that then it should be about as fast as I can make it for practical purposes.

Oct 28, 2008 9:56 AM in response to Gregory Mcintire

Gregory Mcintire wrote:
A little searching turned up this thread:
http://discussions.apple.com/thread.jspa?threadID=1702392&tstart=0

It turns out that the 06 core 2 duo will recognize up to 4GB but only use 3GB if it is a 2+1GB configuration (obvious enough) but it will use 3.2GB if it is a 2+2GB configuration. It should also have very slightly faster video performance with the matched 2+2.


It's the first generation MacBook (Core Duo) that will fail power on self test if more than 2 GB is installed. The 3.3 GB limit on your machine is in the chipset and can't be adjusted.

Really though - PC2-5300/DDR2-667 memory is so cheap these days that the best advice is to just put in as much as you can. Even Crucial has their kits for under $70 right now. They don't show 4 GB kits for your model. Crucial has a policy where their memory finder only lists configurations officially supported by the manufacturer.

http://www.crucial.com/store/mpartspecs.aspx?mtbpoid=2709378FA5CA7304

Oct 28, 2008 10:48 AM in response to Gregory Mcintire

I have a matched pair of 2GB chips in my MacBook even though it won't address it all. Though when I bought them the matched pair was cheaper than the 2+1 kit believe it or not at that time, so it was worth it to me for the "slight" likely not noticably, improvement.

Do what is easiest for you, though. Another reason I did it was I thought I might transfer it to a new macbook late, of course now the

Oct 31, 2008 10:52 AM in response to Gregory Mcintire

I got my new RAM toady and did a comparison of 2, 3 and 4 GB of installed RAM. All three tests were done immediately after a fresh boot.

I realize that XBench is not a thorough test of what can be expected in real world application but I though I would make available to you what I found.
http://members.all2easy.net/gregory/2-3-4GBRAMcomparison.jpg

Only the top half of the results window is shown but as the total score suggests, the variations are quite small in all tests.

RAM and speed increase?

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