I have a quad-core HP Media Centre PC with 4GB RAM (added 2GB after purchase) and an extra internal HD - 1TB 7200rpm. I've got Windows XP and Photoshop CS4 installed on the 1TB drive and partitioned the 500GB into two parts - D: Scratch 100GB (approx) and E: Storage 400GB (approx). Obviously D: is a dedicated scratch disk, containing only the Photoshop temp file, which is about 2GB in size at the moment.

Now, Windows is only seeing 3.25GB of the RAM, which was explained to me in another post as a limitation of XP. When I go to Photoshop, Edit > Preferences > Performance, Photoshop shows 1688MB of RAM only and recommends I assign 928-1215MB to Photoshop. Right now I have it set at the full 1688MB of RAM as I figure Windows can see the other 1.5ish GB and use that.

However, I'm still having problems. At the moment I have 2 files open in Photoshop, both CR2 files 7.69MB in size each. I have pasted one into the other and run Auto-Align layers and tried to run Auto-Blend but it says I don't have enough RAM to complete the operation. This is not the only time I've had this message but its the one that has inspired me to post and see if there is something I can do to improve performance.

What I will do is shut down everything and reboot, which will probably fix the problem.

What I want to know is if there is something I can do to stop it happening. This really doesn't seem acceptable to me, maybe if I had 20 files open and was performing a complex batch, but 2 files?

Also, why does Photoshop only see 1688MB RAM? I read ages ago that CS3 is limited to seeing 2GB, not sure what CS4 is meant to see. Why isn't it seeing the whole 2GB, when I have more than that?

Thanks in advance for your help.

Have you also gone edit>preferences>plug ins and scratch disc and told Photoshop where the scratch disc is ?



Photoshop likes to have the scratch disc (paging file) on a HDD or a partition other than the one it is installed on...........?

Thank you for your quick reply

I can't see where to add it in Plug-ins. Do I choose "Additional Plug-Ins Folder" and choose the D: partition? I thought Plug-Ins were just when programs imbedded into Photoshop so you can use them there, like noiseware filters etc.

In Performance I have clicked the Active? box for my D: partition on my secondary hard drive. Looking at it, do I need to click the others as well so there is backup space? Not that I can see how the 100GB is going to overflow when the Photoshop Temp file is only about 2GB and I have absolutely nothing else on that partition (I partitioned that drive because I read that if you use drive space that is used for other things you need to defrag all the time so there is continuous free space, wheras a dedicated partition will not have other data messing it up - though of course still needs a defrag now and then)

Also, after reboot the total RAM is now showing as 1682MB instead of 1688MB as it was before. Losing RAM at this rate, I'll be out in no time!

ETA: Just to clarify, Photoshop and the operating system are installed on C: - a seperate physical drive to the one that has the scratch disk partition D:.

No, not in the plug-in folder, in preferences.

Maybe I have misled a little as I am still in the dark ages and using CS2, so my route may be a little different to you, but you are looking for something like the attaches screeny where you can see that I have first scratch disc set to point to my slave drive, and the second to my c drive.





As to the leaky ram, perhaps you have a wee hole in the bottom of the tower and it is running out ?

Ah, I think it must just be a difference with the versions.

Here's what mine looks like:



I think you might have something with the hole in the tower theory, may have to drop down to the hardware store and grab some poly-filler!

Well, you need to lower the amount of ram devoted to PS............if you give it 100% as you have done, there is nothing left to run the system.

That figure should be no more than 75% and preferably about 60%-65%.................I know it is tempting to up that figure but something must be left for system  requirements, and frankly 60% of 1.7Gbs of ram is more than enough to run PS.

Make that change and I think the problem will go away..........but it may also be worth a further change in your preferences by pointing PS to the C drive as a secondary scratch disc.



Try these two changes and let us know if there is any improvement.

To expand a little on alumbagh's post, Windows always presents any application with 2GB of address space - in other words a program running on Windows is told it's running in 2GB of memory. The remaining 2GB is used for running Windows itself, and for the addresses of all the hardware in the computer, including the video memory. A 32bit system has only 4GB of addresses in which to fit it all.

Once PS is loaded, the setting in Performance shows how much of the 2GB is unused and still available for PS to pre-allocate (claim for its exclusive use), typically a touch under 1.7GB. Pre-allocating memory helps performance by reducing fragmentation of memory.

But if 100% of the available memory is pre-allocated by PS, nothing else that then needs to operate in the same address space as PS, such as effects plugins, has any memory available to it. Paradoxically, if PS appears to be complaining of insufficient memory, reducing Photoshop's memory allocation may cure it for this reason.

Thank you - I have now reduced the allocated RAM to 70% and hopefully that will fix the problem. I've also ticked C: as a secondary scratch disk.

Not sure if this is the place to ask, but what would be using the other 3-400MB? Windows recognises 3.25GB RAM in System info, why doesn't it use the other 1.25GB for other things? OR are you saying that the 3-400MB is saved by Photoshop for certain processes? Like perhaps the Auto-blend I was trying to do?

Thanks for all the help

ETA: "same address space as PS" .. this sounds like its the key to my question - is there a way to have these things not use the same address space?

It's not obvious what processes will use any given piece of memory. What we can say for sure is that if all available memory is snapped up by Photoshop as soon as it starts, no further memory is available to be allocated for any purpose. Anything that operates in an add-in fashion at some point in Photoshop's operation will want some memory of its own, and I do know Photoshop Plug-ins fall into this category. If you invoke an effect that loads a plug-in, it will definitely need it's own memory space, and some sophisticated plug-ins need a considerable amount. I don't know enough about the internal workings of PS to say if any of its own standard effects operate as a plug-in, only being loaded if called on, but it's not an unusual way to limit the size and enhance the loading speed of a large application.

The limitation of a 32bit system having a 4GB total address space is the reason for the present transition to 64bit Operating Systems and applications. With 32bit, everything that needs an address (for both the processor and the operating system to be able to find and use it) has to fit within that space. In your system, the top 3/4 of a GB is used for everything that is needed to access all the hardware in the system - every device, on every bus, your sound, video card and things like some tables of information that Windows needs to manage virtual memory etc. How much space this takes up varies from system to system, yours is fairly typical.

The other 1.25 GB is used for the place for Windows itself to be. The code that provides all of Windows operation, all the device drivers and all the shared resources that need to be available to each of the applications installed on your system, eg function .DLLs (libraries) go here. So it's not wasted, in fact as operating systems have become larger, it's become a bit tight.

The remaining 2GB of address space is available for Windows to provide for applications to run in. Due to some neat trickery in the way the processor runs in what's called 32bit (386) Protected Mode, more than one application can each be "given" what to it appears to be 2GB of memory. Protected Mode prevents an application in one 2GB memory space from accessing memory that "belongs" to another application in its own 2GB space, so that programs can't interfere with each other's operation, and one program crashing will probably not crash Windows or other programs running at the same time. So things that interact directly, like Photoshop and a plug-in, have to be in the same address space, or they are prevented from having access to each other's memory where the data (ie image) is.

There is a way to increase the application address space to 3GB ( the /3GB switch), if an application has been created so as to be capable of utilizing this (Photoshop has). But in most cases it's of no practical value, since the extra 1GB of space has to come from somewhere, and it's taken away from the Operating System. So Windows has to squash into 1GB less space, which means Windows will run badly, being very slow and probably frequently crashing.