[mduell]

There are four memory tradeoffs to be made: capacity, bandwidth, latency and cost. You get to pick two (sometimes three) and the last one or two are forced upon you.

The FB-DIMM memory architecture was designed to have a high capacity ceiling and high bandwidth, but it comes with the downside of high latency and high cost. That said there are still tradeoffs you can make to keep latency or cost down at the expense of something else.

[SierraDragon]

Originally Posted by misterdna 

...Bottom line, are you saying Allens 10GB recommendation (4x2 + 2x1) indeed trumps my attempt to follow the BearFeats 14GB set-up (6x2 + 2x1)?...

I went with removing 2x512 to add 4x2GB. Then I will add 4x4GB when 4-GB sized DIMM prices fall some more. But your 6x2 + 2x1 is OK too.

-Allen

[OreoCookie]

Keep in mind that all current Adobe pro apps are 32 bit (Lightroom 2 will be 64 bit, but it's in its early beta stages). Photoshop will remain 32 bit for at least another version, so only CS5 might be 64 bit. This means after adding appropriate amounts of memory, you won't see a speedup. Aperture is a 64 bit app, so it can access all of the memory you have installed.

It's alright if you start with 8 GB and watch your free memory. If you have any appreciable free memory (have a look at Activity Monitor), then you have enough RAM. I. e. this means, you have so much RAM that OS X doesn't know what to do with it.

The number to watch is the number of page-outs in Activity Monitor. If you have few page-outs (up to a few hundred), then everything you do fits into the RAM you have installed and putting more memory into your machine won't give you any speedups whatsoever.

Edit: Do not monitor free RAM, Ideally OS X uses up all available memory. Free RAM is wasted RAM. Also, apparently Leopard's Activity doesn't show the number of page-ins and page-outs anymore, but the amount (in MB/GB). So either you check the number of page-ins and page-outs in MB/GB or do the following to get the number of pageouts: Launch Terminal (located in /Applications/Utilities) and type `vm_stat' (without quotes).

[ninahagen]

Originally Posted by OreoCookie 

Keep in mind that all current Adobe pro apps are 32 bit (Lightroom 2 will be 64 bit, but it's in its early beta stages). Photoshop will remain 32 bit for at least another version, so only CS5 might be 64 bit. This means after adding appropriate amounts of memory, you won't see a speedup. Aperture is a 64 bit app, so it can access all of the memory you have installed.

It's alright if you start with 8 GB and watch your free memory. If you have any appreciable free memory (have a look at Activity Monitor), then you have enough RAM. I. e. this means, you have so much RAM that OS X doesn't know what to do with it.

The number to watch is the number of page-outs in Activity Monitor. If you have few page-outs (up to a few hundred), then everything you do fits into the RAM you have installed and putting more memory into your machine won't give you any speedups whatsoever.

I think that is the best I have ever heard it put.

[SierraDragon]

Originally Posted by OreoCookie 

Keep in mind that all current Adobe pro apps are 32 bit (Lightroom 2 will be 64 bit, but it's in its early beta stages). Photoshop will remain 32 bit for at least another version, so only CS5 might be 64 bit. This means after adding appropriate amounts of memory, you won't see a speedup...

That is a very misleading statement. Athough PS can only directly address ~3 GB RAM, usage of a complex app like PS is not that simplistic. For years, even under PSCS2, PS operation has readily shown improvement with up to 8 GB of RAM on board because of the OS/app interaction. Under OS 10.5.2 and PSCS3 improvement can be seen with 16 GB RAM and probably beyond that.

The performance of hugely complex apps like Aperture or PS is extraordinarily complicated and irrevocably intertwined with the OS and computer hardware. Issues like memory bandwidth (a major bottleneck), 32/64 bit, multi-core operation, etc. are dealt with in OS code and app code as well as in hardware. E.g. Apple apparently worked some coding magic to help cope with limiting memory bandwidth on the new MPs. Moving forward we can expect similar efforts in other areas as well.

RAM is now cheap and users should expect that irrespective of 32 vs. 64 bit app design the operation of evolving generations of heavy graphics apps under evolving versions of OS X will continue to increasingly take advantage of larger amounts of RAM.

Activity Monitor is very useful, but I also think folks should actually empirically test timed operations within their own workflows, as well as the "feel" of operations under different setups. For PS in particular there are also some setup tricks like Bigger Tiles that can be relevant for differing workflows.

-Allen Wicks

[OreoCookie]

I suggested a more than reasonable amount of RAM, almost three times as much as Photoshop can use and then see if -- under typical use -- more RAM is necessary. Anything beyond the 3 GB + what OS X uses will be used by other apps. It's not about the `complexity' of Photoshop at all. OS X couldn't care less how (up to!) 3 GB RAM are used, the `complexity' of PS doesn't enter.

If there are no pageouts at 8 GB, of course, you won't have any at 16 GB. But on the other hand, you've wasted money on 8 GB you don't need and could have spent on something else. The other eternal truth of the computer industry is that whatever you buy now, you can have it for less in six months. People should buy RAM when they need it.

So start with a reasonable amount and watch your pageouts!

[SierraDragon]

Originally Posted by OreoCookie 

...OS X couldn't care less how (up to!) 3 GB RAM are used, the `complexity' of PS doesn't enter.

The complexity that I reference is the interaction of OS X and PS. That complex interaction in many ways obviates the concept of PS only directly addressing ~3 GB OF RAM and IMO folks need to largely lose that 3 GB limitation from their thinking since we have known for years that at least 8 GB is often beneficial.

If there are no pageouts at 8 GB, of course, you won't have any at 16 GB. But on the other hand, you've wasted money on 8 GB you don't need and could have spent on something else. The other eternal truth of the computer industry is that whatever you buy now, you can have it for less in six months. People should buy RAM when they need it. So start with a reasonable amount and watch your pageouts!

I more than fully concur. My MP currently has 8 GB RAM in matched 2GB-sized DIMMs. However I will add 4x4GB for 24 GB total once the price of 4GB-sized DIMMs falls sufficiently because I know that heavy apps and the OS will evolve (another eternal truth of the computer industry) to take advantage of more and more RAM. Also I am an Aperture user and AFAIK the upper limit of RAM benefit to Aperture's performance remains undefined.

Although I consider Activity Monitor very, very useful I am not convinced that watching for reported pageouts is all there is to optimizing a box. There are just too many (changing) complex interactions involved among apps and the OS. IMO we should also empirically be time-testing our setups. Some PS engineers have already found 16 GB RAM beneficial. Of course for lighter levels of work higher RAM amounts provide no benefit.

-Allen Wicks

[misterdna]

Before you guys started talking about it, I never used Activity Monitor or heard of page outs. I'm still trying to get a handle on what it means. Currently, an interesting discussion of pagouts is going on here:
Page outs with 12 gigs of ram? - Mac Forums

[OreoCookie]

@misterdna
pageouts are the times when data that is needed right now cannot be stored in the RAM and has to be stored on the harddrive. It is probably the most important criterion on choosing the amount of RAM you have to get so that you don't see any performance degradation.

So just to make this clear: if you have a few hundred to thousand pageouts, you will not see any improvement in performance by putting in more memory (given that you will use your computer in the same way as before), simply because you don't use more! 8 GB is more than a safe amount to start with.

Free RAM is not a good criterion, because OS X will try to load as many things into the RAM as possible (so that applications that need pieces of the OS don't have to be waited until they are loaded into the RAM). Call it foresight of the OS. It's probably one of the most frequently asked noob questions regarding memory: I don't have any free memory, what's wrong with my computer?

@Sierra Dragon
pageouts is the most meaningful criterion, because it measures the occurrences when something did not fit into your RAM and had to be swapped onto your harddrive. If that number is 0, it means, your needs have never exceeded the available memory! You will get 0 performance improvement if you put in more. In this sense the number of pageouts (which is displayed in Activity Monitor) is the best criterion I'm aware of whether you need more RAM.

Now optimizing the amount of RAM is not the only thing that makes your box faster, yes, but we're just talking about RAM at the moment. Having more than 4 GB of RAM is beneficial, because we have multitasking. If you have another RAM hog running alongside Photoshop (which can boost productivity, no question about it), then yes, more RAM (e. g. 8 GB) will improve your system's performance.

Perhaps you need more RAM later, but I see nothing wrong with a `buy it when you need it' attitude, even and especially in a professional environment. Putting 24 GB RAM into a machine you will replace in two, three years does not make sense to me.

[SierraDragon]

FWIW with PS open but doing nothing, and scrolling thru a 1300-image wedding in Aperture I quickly add a few thousand pageouts. This is with 8 GB RAM, 2.66 GHz MP. No lag in Aperture, full screen sized images scroll instantly.

-Allen Wicks

[OreoCookie]

See about my comment about page-outs, where is the contradiction to what I've said?

Originally Posted by OreoCookie

So just to make this clear: if you have a few hundred to thousand pageouts, you will not see any improvement in performance by putting in more memory …

People should think about upgrades if they see hundreds of thousands of pageouts.

[misterdna]

Speaking of RAM (even though this was originally a RAID thread), anyone see this chart showing how the configuration of your RAM makes a lot of difference on the early 2008 Mac Pro?

(Scroll down to the 8-core chart)

OtherWorldComputing.com

[SierraDragon]

Originally Posted by OreoCookie 

See about my comment about page-outs, where is the contradiction to what I've said? People should think about upgrades if they see hundreds of thousands of pageouts.

Oreo-

I am not contradicting, just observing. If I see a few thousand pageouts in under a minute it is clear to me that RAM beyond my existing 8 GB would likely be beneficial. And I am all about configuring boxes for the future rather than for last week; the OS, apps, Library growth, falling RAM prices, etc. all mediate toward even more benefits from additional RAM as time goes on.

-Allen Wicks

[mduell]

Originally Posted by misterdna 

Speaking of RAM (even though this was originally a RAID thread), anyone see this chart showing how the configuration of your RAM makes a lot of difference on the early 2008 Mac Pro?

(Scroll down to the 8-core chart)

OtherWorldComputing.com

There's nothing particularly insightful from that testing. That's what I've been saying all along from reading the Intel tech docs.