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XP and RAM

UberSkippy

a.k.a. FuckTheBullShit
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#1
Ok, so this is more for work than my own knowledge but I'm having some trouble figuring an issue out.

I have a user who has 2 Gigs of physical RAM and a 3 Gig swap file. Now correct me if I'm wrong but XP can really only address 4 Gigs total. That's Physical and Virtual RAM combined right? So in this instance she's got 5 Gigs which would be 1 over the limit.

Assuming that the 4 Gig limit theory holds true it would be safe to expect that if she ran a memory intensive app and addressed something in that 5th Gig we would expect strange behaviors correct?

What's happening is that while running some software that renders it's own graphics she gets an error and the file she's working in gets corrupted. We can't figure out how or why that's happening. It appears that she's got a bad memory stick but when we test them they're fine and she's reported no other issues. With a bad memory stick I would expect odd random errors, blue screens and the like.

IT guys, your thoughts?
 

rcarhar

There goes a clever gent
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#2
Have you simply tried toning down the swap file to 1 or 2 gigs and then running such tests? I'd reccomend it.
Bad RAM does give you unwanted behavior, and I don't see a need for a 3 gig swap file, esp. with 2 gigs of phys. RAM. (in most cases)
 

UberSkippy

a.k.a. FuckTheBullShit
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#3
rcarhar said:
Have you simply tried toning down the swap file to 1 or 2 gigs and then running such tests? I'd reccomend it.
Bad RAM does give you unwanted behavior, and I don't see a need for a 3 gig swap file, esp. with 2 gigs of phys. RAM. (in most cases)
That was exactly my thinking. I doubt the RAM is the problem as no other issues are seen with this system. Just the one application has problems. Other apps, and the OS itself, run just fine.

Edit: And if you think about it, since Microsoft's suggested minimum swap file is 1.5 x RAM the 3 gig makes sense. In a Microsoft logic sort of way.
 

Broken

Member smoked too much weed!
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#4
UberSkippy said:
Ok, so this is more for work than my own knowledge but I'm having some trouble figuring an issue out.

Assuming that the 4 Gig limit theory holds true it would be safe to expect that if she ran a memory intensive app and addressed something in that 5th Gig we would expect strange behaviors correct?
First, the four gig limit isn't a theory. It's the fact that it's a 32bit proc, and OS.
By definition, a 32-bit processor uses 32 bits to refer to the location of each byte of memory. Which means a memory address that's 32 bits long can only refer to 4.2 billion unique locations (i.e. 4 GB)
each application has its own “virtual” 4GB memory space. (This means that each application functions as if it has a flat 4GB of memory, and the system's memory manager keeps track of memory mapping, which applications are using which memory, page file management,etc.
This 4GB space is evenly divided into two parts, with 2GB dedicated for kernel usage, and 2GB left for application usage. Each application gets its own 2GB, but all applications have to share the same 2GB kernel space.

And blah blah blah.

That the basic Idea, I am drinking and if something is off a bit. Fuck you. drive through, and yes there are reg hacks.
 

Jung

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#5
Broken said:
First, the four gig limit isn't a theory. It's the fact that it's a 32bit proc, and OS.
By definition, a 32-bit processor uses 32 bits to refer to the location of each byte of memory. Which means a memory address that's 32 bits long can only refer to 4.2 billion unique locations (i.e. 4 GB)
Actually, every modern 32-bit processor uses a 36-bit Physical Address Extension, which allows them to support up to 64GB of RAM. However, most non-server OSes don't support more than 4GB.




I'll jump on the bad ram bandwagon as well; Try running www.memtest86.com or www.memtest.org.

rcarhar said:
Have you simply tried toning down the swap file to 1 or 2 gigs and then running such tests? I'd reccomend it.
I don't see what that would have to do with anything. :confused:

Those programs only test physical memory, not virtual memory, which is just hard disk space allocated as memory inside the OS. Outside that OS, virtual memory is just hard disk space. When you're booting into memtest, the PC doesn't know about VM at such a high level.


Side note: XP 64bit edition will support up to 128GB of physical memory.
 

UberSkippy

a.k.a. FuckTheBullShit
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#6
Jung, thanks for the input. We've already done the memtest.

The problem lies in the fact that a certain peice of high end software is having major issues. Other than that, the system is quite stable. The software in question uses a lot of RAM so the current theory is that with the 4 gig limit being exceeded in XP that chunks of data are being lost simply because XP is addressing a gig of memory it shouldn't be.

Outside of this software, the system is very stable. Trace files from the software don't show any problems.
 

Jung

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#7
I don't see why XP would be addressing an extra gig of memory; it handles VM and physical memory differently. Surely you can get support from either Microsoft or the vendor of the software in question though. I guess you could try running with less than 4GB, but I seriously doubt that's a problem.

Just out of curiosity, you are running XP Pro on this machine, right?
 

UberSkippy

a.k.a. FuckTheBullShit
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#9
Broken said:
What is the high-end software?
Saddly, I'm not really allowed to say that. The boss is... sensitive to where the name of his product is used.
 

Jung

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#10
Maybe you could give us a decent idea of what it actually does then? What is it used for, what kind of images is it creating, etc. I mean if it's creating small pngs or jpgs it's probably negligible, but if you're creating high res topo maps in tiffs format or something, then it could be a problem with needing more memory, which would mean dumping XP all together.
 

UberSkippy

a.k.a. FuckTheBullShit
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#11
It's multi-media presentation software capable of rendering live 3d effects as a motion background for stills, text and such. It's minimum requirements to use the higer end graphics features include a 1 GHz processor, 1 GB of ram and a higher end graphics card. (Like the 6800 or x800 cards).

Some of the features include rendering 3d effects on the fly and using them as a moving background, using any video file format as a background, colorizing photos, videos or live video, adding sound effects and doing it all on the fly.

This particular user is having problems with her files being corrupted. Essentially, the file that's saved is a simple binary file that contains links to various databases which contains portions of her presentation. When she saves the file it's being corrupted. She's basically only saving the header for her presentation without any of the links or the End Of File. The reason it's so hard to figure out is that it doesn't happen consistently, she's the only user with the problem and the system (according to her) has no other problematic behavior.

I'd really like to tell you guys more but this guy would shit if he found out I posted about it here. He's got his own forum and he polices that like a nazi. Anything we want to post has to be pre-approved by him.
 

Jung

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#12
The only reasons I can see for data corruption would be:

1) Faulty drives/file system
2) Faulty RAM; data is getting corrupted either when paging in or out of RAM
3) Faulty processor; fp/int calculations aren't being properly solved

Faulty RAM can actually destroy a perfectly good file system for the reason I stated above.


Can you try running Prime95 over night and see what happens? Prime95 will run fp calclations with set answers, it'll then check the answers your PC returns against known good ones. If you get errors, you know one of the three is likely happening. http://www.mersenne.org/freesoft.htm

Windows doesn't do a massive amount of fp math, neither do the control loops of almost all programs. This is all done in int for various reasons. Rounding errors mainly effect the accuracy of results, not the stability of programs. So rather than crash outright, you're more likely to get misrendered frames in video encodeing/decoding, corrupted files on disk, or 3d graphics being misrendered or corrupted. This *may* be the case in your situation. I've seen it before.
 

UberSkippy

a.k.a. FuckTheBullShit
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#13
This sounds very plausible. I took some time to go through the trace files again and there is a hint of something in there. I'll have our visuals guy look at it but I suspect he's going to tell me it's a memory issue.

Thanks for the help.