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Giving ZBrush 3GB on 32bit XP with Physical Address Extensions enabled

ZBrush Usage Questions
#1

My Windows XP Pro (32bit) is set with Physical Address Extensions (/PAE) in the Boot.ini (actually, I have /NoExecute=OptIn set, which implies /PAE and thus turns it on from what I understand).

I have 4GB RAM installed and looking at my system properties (right click ‘My Computer’) shows 3.5GB memory AND Physical Address Extension - so I guess PAE is active.

I have also created a boot option with the /3GB switch set which is meant to allow Large Address Aware applications to be able to allocate up to 3GB for their use, rather than the 2GB max.

I’m assuming that ZBrush is Large Address Aware.

I’ve set the Preferences>Mem>Compact setting to 3072 (3GB?) in the hopes that it will take all the mem that the /3GB and Physical Address extension will give it.

However, while running ZBrush with the Windows Taks Manager showing the Processes, I can see that the ZBrush.exe process does not ever go above around 2GB in mem usage.

Can anyone shed light on this?

#2

ZBrush can use up to 4 GB of RAM.

With the /3GB switch, that theoretically means that it can use the 3 GB under a 32-bit version of Windows. Unfortunately, theoretically does not always work out.

That /3GB switch is unsupported by Microsoft. In other words, they know it doesn’t always do what it’s supposed to. For some computers, it works like a charm. For others, it makes things worse.

The only reliable way to get more RAM to ZBrush is by using a 64-bit version of Windows.

#3

Thanks Aurick,

That’s kind of sucky, if I’m one of those people for whom the /3GB switch doesn’t work. Luck of the draw, eh. I have to say, I haven’t encountered any worsening of the system’s reliability with the /3GB switch, for what its worth.

I’m kind of shocked that if I move to 64 bit windows, 4GB memory allocation is the limit. Considering that its not too expensive these days to go above that. Is the 4GB limit a ZBrush thing only?

If anyone is sitting on any information that might turn things around, please spill some beans :wink:

Thanks for your help, aurick.

#4

Bear in mind that the OS system will always take a sizeable chunk of RAM. And if you want to run other programs at the same time - for example Photoshop for ZAppLink - they’ll need some too. So in order for ZBrush to have 4GB available you’d probably need 6GB installed.

#5

OK, I think I have the /3GB app allocation on 32bit windows working now.

I found that my windows virtual memory page file was explicitly set to below te recommended limit for the new amount of RAM onboard (I had upped it to 4GB from 2GB). So I set the to page file to ‘System Managed Size’ and it seems that there is more actual RAM available to dish out.

I’ve been able to increase model complexity beyond what I could before, and windows task manager has shown memory allocation on ZBrush go beyond 2.5GB so far - so I guess it must be working.

#6

Ideally, the system’s page file min and max settings should both be twice the amount of RAM that you have. Letting Windows manage it is something that performance experts almost always say never to do.

Also, put the page file on a different physical drive from the operating system if at all possible.

#7

Thanks so much for the advice, Aurick.

Just to confirm:

Does this mean that the min and max settings should be the same value?

So, if I have 4GB installed on 32bit XP and the OS is only capable of seeing 3.5GB, then the min and max settings should ideally be set to 7GB ?

#8

Yes, having the same values is what is recommended by the performance experts. As for the value that you need, 7 or 8 would be fine. Better to have too much than too little.