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Old 05-22-10, 05:05 PM   #1
chewybrian 
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Computer people--What is "virtual memory"?

My computer kept telling me something like:

"Your system is low on virtual memory; certain functions will be limited while the computer attempts to expand..."

But, it was never able to get it right, and the system would sometimes crash. So--one in a million shot--I tried to fix it myself. I went to help, typed "virtual memory", followed the directions given, and... problem solved!

I doubled the size of the virtual memory file, and all the problems went away. So, what exactly did I do? Is there any risk in it? Is this a common problem that people might mistake for a virus or something else?

I'm guessing it is not common. It looked like the prior owner had a custom setting, instead of letting the computer pick it. The recommended setting was much higher than what was set.
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Old 05-22-10, 05:12 PM   #2
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If you can see it and it's there - it's real
If you can see it and it's not there - it's virtual
If you can't see it and it's not there - you erased it.

See virtual memory.
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Old 05-22-10, 05:37 PM   #3
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Quote:
Originally Posted by StupidlyBrave View Post

Yes, I actually went to Wiki first, but when I read:

"...Virtual memory differs significantly from memory virtualization in that virtual memory allows resources to be virtualized as memory for a specific system, as opposed to a large pool of memory being virtualized as smaller pools for many different systems..."

Well, my DNA based cognitive system became low on virtual comprehension. While attempting to expand comprehension, I may appear to understand the concept even less than when I began reading... Dumb it down for me, man.

I guess my hard drive had space available to use for this purpose, but the setting would not let it take the space. So, I expanded the space it was allowed to use, and the process was able to proceed as it should have all along. It somehow uses disc storage to fool the computer, or the program, into thinking it is using more memory than it is actually using(?). That's the part I'm really not getting.
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Old 05-22-10, 05:57 PM   #4
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Have you ever defragmented your hard drive? If you haven't, please do it soon. (If you have a Mac, this won't apply.)

If you have, then you'll know that your memory usage is all chopped up into bits and pieces - fragmented. Sort of like when you take books off the shelf and leave empty spaces in between the rest of the books. Now, when you come along with a really large book (aka program), the computer thinks there isn't any memory left to run the program because there aren't any spaces left that are big enough for it. It doesn't try to push all the books to one end and leave a bigger space for you to jam the book in. That's where virtual memory comes in handy - it joins up the spaces so you have enough memory to run your program.

Short version: expanding your virtual memory is perfectly fine and will help your computer run better. Unless you are using a specialized high performance machine, in which case you know more about computers than I do.
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Old 05-22-10, 05:59 PM   #5
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Quote:
Originally Posted by chewybrian View Post
I guess my hard drive had space available to use for this purpose, but the setting would not let it take the space. So, I expanded the space it was allowed to use, and the process was able to proceed as it should have all along. It somehow uses disc storage to fool the computer, or the program, into thinking it is using more memory than it is actually using(?). That's the part I'm really not getting.
You basically got it.

Virtual memory is when your hard disk is used to store information that would normally be held in physical memory. While much slower than physical memory, it can prevent programs from using up all the physical memory and crashing. While this sounds like it would slow your computer down a great deal, in practice it doesn't because memory for programs that are not being actively used get paged to disk so that the ones that are being used take advantage of your real memory.
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Old 05-22-10, 06:05 PM   #6
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Quote:
Originally Posted by chewybrian View Post
Yes, I actually went to Wiki first, but when I read:

"...Virtual memory differs significantly from memory virtualization in that virtual memory allows resources to be virtualized as memory for a specific system, as opposed to a large pool of memory being virtualized as smaller pools for many different systems..."

I guess my hard drive had space available to use for this purpose, but the setting would not let it take the space. So, I expanded the space it was allowed to use, and the process was able to proceed as it should have all along. It somehow uses disc storage to fool the computer, or the program, into thinking it is using more memory than it is actually using(?). That's the part I'm really not getting.
The memory virtualization as described in the wiki sounds more like a clustered computer environment, don't worry about it. I think you could compare it to multiple desktop computers all communicatively linked together and letting them use each other's RAM (all under the control of the OS).

I believe the OS uses a large file for the swap file and it's usually the same size (until it needs to get bigger). Some people reduce the size of this because it takes up hard drive space, but this is moot with today's massive hard drives. Just let the OS handle it (preferred) or set it to 1.5 times your physical memory (I think?).

When you start up Word.exe, Word starts using memory, let's say starting at physical location "0" and goes to location "5". Then you start up Excel and it needs memory too. The next physical location available is 6. If excel stores something there, Word cannot use that space. Now both Word and Excel have to keep track of who is using which physical address, which is inefficient. The solution is to give each program its own virtual memory address space. Word uses virtual locations 0 to 5, and excel gets its own space... it starts with its own virtual location 0. The operating system uses a mapping function to figure out that 0-5 for Word goes to 0-5 in physical memory, and 0 for excel goes to 6 for physical memory. What if you run out of physical memory? the OS simply uses the mapping function to point to the hard drive instead of RAM. Word and excel only ever see their virtual space, they don't care whether it ends up in RAM or on the hard drive.
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Old 05-22-10, 06:14 PM   #7
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Quote:
Originally Posted by chewybrian View Post
My computer kept telling me something like:

"Your system is low on virtual memory; certain functions will be limited while the computer attempts to expand..."

But, it was never able to get it right, and the system would sometimes crash. So--one in a million shot--I tried to fix it myself. I went to help, typed "virtual memory", followed the directions given, and... problem solved!

I doubled the size of the virtual memory file, and all the problems went away. So, what exactly did I do? Is there any risk in it? Is this a common problem that people might mistake for a virus or something else?

I'm guessing it is not common. It looked like the prior owner had a custom setting, instead of letting the computer pick it. The recommended setting was much higher than what was set.
They might have wanted the harddrive space more than they wanted program performance. They probably got rid of the computer because that kept crashing stuff.

If that machine will take more RAM, it'll run a lot better with RAM maxed out.

I don't think I'd suspect a virus, as many of them are pretty svelte and attempt to run undetected.

Photoshop and other graphics and video programs demand TONS of virtual memory if you don't have TONS of RAM.
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Old 05-22-10, 06:17 PM   #8
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So does anybody have a favorite way to defragment windows xp computers?
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Old 05-22-10, 06:35 PM   #9
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I use the one in the Start menu (Accessories>System Tools>Disk Defragmenter) on the work computers. I have a Mac at home, so I haven't looked into downloading any third-party programs. (Work computers just aren't worth the effort, )
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Old 05-22-10, 07:03 PM   #10
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This is a pretty good explanation: The thing king and the paging game.
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Old 05-23-10, 12:09 AM   #11
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So does anybody have a favorite way to defragment windows xp computers?
Yes, uninstall it, and install Ubuntu. lol
Virtual Memory is what happens when you move to CA and get a hook up for medical marijuana.
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Old 05-23-10, 02:05 AM   #12
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Have you ever defragmented your hard drive? If you haven't, please do it soon...
As long as you have no follow up questions, then, um, yeah sure. I do it every week after defrosting the freezer and changing my timing belt.

Quote:
Originally Posted by coffeecake View Post
...memory usage is all chopped up into bits and pieces - fragmented. Sort of like when you take books off the shelf and leave empty spaces in between the rest of the books. Now, when you come along with a really large book (aka program), the computer thinks there isn't any memory left to run the program because there aren't any spaces left that are big enough for it. It doesn't try to push all the books to one end and leave a bigger space for you to jam the book in. That's where virtual memory comes in handy - it joins up the spaces so you have enough memory to run your program...
The book shelf analogy was useful; I am starting to get it (a bit). This goes back to grade school math with me. I was never happy to get the answers unless I understood what they meant, why they worked.


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Originally Posted by coffeecake View Post
I use the one in the Start menu (Accessories>System Tools>Disk Defragmenter) ...
Though I frequently do this, it's helpful to have this reminder just in case I forget the steps. Seriously, I probably would never have tried this until I did the virtual memory trick. I had assumed I just had a p00py old computer, but the change really increased its performance. So, perhaps the de-frag could help even more (probably can't hurt).

Quote:
Originally Posted by StupidlyBrave View Post
This is a pretty good explanation: The thing king and the paging game.
Judging from this. I must not be the only non tech support guy who didn't pick this up on the first bounce.

Thanks to everyone who replied. Foo always has all the answers.
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Old 05-23-10, 03:53 AM   #13
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Virtual memory is space on your hard drive that the computer system uses to pretend that it's got more RAM than it actually has. Programs too large to run in the physical RAM can still run by swapping portions of both program and data to and from the disc. The default in Windows XP was to allocate space 1.5 times the size of your actual physical RAM...which really is quite stupid, since smaller physical RAM would necessitate larger virtual memory space, not less. Windows XP handling of virtual memory seems rather poor in other ways, too...there appears to be much more use of virtual memory and much more disc I/O than actually required. Virtual memory usage seems to occur even when there's plenty of free space in the RAM.
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Old 05-23-10, 05:44 AM   #14
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So does anybody have a favorite way to defragment windows xp computers?
START/RUN CMD[enter] defrag c: [enter]

Subsistute other drives for c: as needed.
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Old 05-23-10, 06:43 AM   #15
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Hey chewy, the reason why I asked whether or not you'd defragged it is because it shows you a nice little diagram of your memory usage before and after defragging. Doesn't hurt to have a visual . Also, it's the third thing I say when helping people with their computers, after "Have you tried restarting it?" and "Is it plugged in to the wall?"
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Old 05-23-10, 07:37 AM   #16
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Hey chewy, the reason why I asked whether or not you'd defragged it is because it shows you a nice little diagram of your memory usage before and after defragging. Doesn't hurt to have a visual . Also, it's the third thing I say when helping people with their computers, after "Have you tried restarting it?" and "Is it plugged in to the wall?"
Well, I did the de-frag, and I did see the bookshelf, before and after. It didn't help performance that I noticed, but I can't imagine it did any harm. It's sort of like upgrading to Dura-Ace, eh?
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Old 05-23-10, 10:24 AM   #17
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Virtual memory is the one that goes in one ear and out the other.
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