Windows 8 and 8.1 Forums


Do you really need Virtual Memory?

  1. #11


    Posts : 1,925
    Windows 8.1 Pro


    If you're setting up a RAM drive, then you're taking away your extra memory.. I would definitely re-enable virtual memory in that case.

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  2. #12


    There's more going on under the hood. Generally speaking, Windows maintains a backing store, meaning that it wants to see everything that's in memory also on the disk somewhere. Now, when something comes along and demands a lot of memory, Windows can clear RAM very quickly, because that data is already on disk, ready to be paged back into RAM if it is called for. So it can be said that much of what's in pagefile is also in RAM; the data was preemptively placed in pagefile to speed up new memory allocation demands.
    Interesting part of the article !

    ram drive
    It's another point here !

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  3. #13


    I just built myself a new system and with 16GB of memory, I have turned off the virtual memory. It seems to me that real memory is faster than swapping things back and forth from a hard drive and it should save wear and tear on the hard drive. Maybe the operating system only uses the pagefile if it runs out of real memory?
    Virtual memory isn't something that can be turned on or off. It is a central concept in Windows memory management, as important to how the OS operates as a heart and lungs are to you and I.

    Virtual memory is a complex system involving the CPU and OS. This system provides to each process a private virtual environment with an address space of 2 GB (in a 32 bit OS) in which code and data is stored. Note that the size of this address space is completely independent of RAM size. To a process this is what memory is. A process knows nothing of how much RAM is in the system, where it is, or how it is being used. RAM is managed by the system memory manager and it's operation is completely transparent to an application. A process can learn some of these detains but few do, it being little more than useless trivia.

    This concept of virtual memory is nothing new, being used in every Windows server and desktop OS for some 20 years. And it has been used in large computer systems since the 1960s. Linux and Mac OS X follow the same principles, differing only in the details.

    A virtual memory system offers many advantages to both developers and computer users alike. Modern operating systems wouldn't have near the capabilities they have without it. Unless the system is under severe memory pressure the performance is very good.

    Unfortunately, Microsoft has done little to educate the public about this. In fact, many computer professionals lack even a basic understanding. In much user level documentation it is described as "using a file on the hard disk as if it were RAM". A serious misrepresentation if ever there was one, and one that been the cause of much unwarranted criticism of how Windows manages memory.

    The pagefile is a small but important part of the virtual memory system. It's purpose is to optimize the operation of the system and it generally works very well. It works by providing a place where the memory manager can store rarely used data, thus relieving RAM of this burden and allowing it to do what it does best.

    Unless you have a specific need and you understand what you are doing (and you can't learn this by reading a few forum posts) it is best to leave pagefile configuration on default settings. Many people have disabled the pagefile in the belief they are benefiting performance. In most cases they are only fooling themselves.
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  4. #14


    Posts : 1,925
    Windows 8.1 Pro


    Quote Originally Posted by LMiller7 View Post
    Virtual memory isn't something that can be turned on or off. It is a central concept in Windows memory management, as important to how the OS operates as a heart and lungs are to you and I.
    He's talking about swapfile size. Yes, Virtual Memory is a very overloaded term, I've given up trying to educate people on that.
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  5. #15


    Sloe Deth, Californicatia
    Posts : 3,908
    Windows 8 Pro with Media Center/Windows 7


    Well with 16 GB of Ram, try it. Then Open a Blue Ray Movie if you have one on disk, see what happens when you try to play it. Or, if you have a BR Player on your system. If the movie file is 30 GB or larger, will it load all of it into VLC or whatever Video Player you use? Or will it just load the Video and Audio as needed by the Program?

    If you are running a program that LOADS a 30-GB file, it may choke on that without the Virtual Memory. But you can try it out and see what happens. I'd be eager to see how the system runs without Virtual Memory.
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  6. #16


    Posts : 94
    Microsoft Windows 8.1 Pro 64-bit


    Quote Originally Posted by alkaufmann View Post
    I just built myself a new system and with 16GB of memory, I have turned off the virtual memory. It seems to me that real memory is faster than swapping things back and forth from a hard drive and it should save wear and tear on the hard drive. Maybe the operating system only uses the pagefile if it runs out of real memory?
    Ak
    Leave it as default, really, its been discussed for ages, unless you use a very short capacity ssd and you're very low on space to hold the pagefile, dont mess with it.
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  7. #17


    Posts : 454
    Windows 8.1 Pro with Media Center


    Quote Originally Posted by alkaufmann View Post
    Lets say I set up a maximum 4GB of virtual memory and I have 16GB of actual ram, what would happen if an application requires 30GB of ram? Would I get the blue screen of death with some system code or would the application tell me I do not have enough memory?
    The attempted allocation would fail, and the program making the attempt would react however it reacts. Well-written programs would handle the issue gracefully. Less well-written programs would tend to crash immediately as they try to access memory through a null pointer. Terribly written programs would run for a while longer and corrupt something totally unrelated.
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  8. #18


    Posts : 1,925
    Windows 8.1 Pro


    Quote Originally Posted by crawfish View Post
    The attempted allocation would fail, and the program making the attempt would react however it reacts. Well-written programs would handle the issue gracefully. Less well-written programs would tend to crash immediately as they try to access memory through a null pointer. Terribly written programs would run for a while longer and corrupt something totally unrelated.
    Almost no application can be well written enough to deal with out of memory conditions, because there are simply way too many uses of memory in the system.. an app has to be written very specially to be able to survive this, and typically is only done in real-time systems.
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  9. #19


    Posts : 454
    Windows 8.1 Pro with Media Center


    Quote Originally Posted by Mystere View Post
    Almost no application can be well written enough to deal with out of memory conditions, because there are simply way too many uses of memory in the system.. an app has to be written very specially to be able to survive this, and typically is only done in real-time systems.
    It does depend on the nature of the failed allocation and what you mean by "deal with". A program that attempts to allocate a huge array and can't handle it gracefully is a terribly written program, period. As for smaller allocations that are expected to never fail, in a C++ program, a failed new would throw an exception, the stack would be unwound, destructors for local objects would run, and the program would remain in a well-defined state. You do need to avoid dynamic memory allocation in your recovery code, and while that can be subtle, recovery code is normally about releasing resources, not acquiring new ones. For some programs, terminating immediately might be an acceptable "graceful" response. What should not be done is to pretend memory allocation cannot fail and to continue on blithely after it does such that the problem manifests in code possibly far removed from the allocation, such that memory allocation failure is indistinguishable from a program bug.

    That said, if normal small allocations start to fail in a virtual memory system, the system as a whole will likely have become unusable due to pagefile thrashing, which is something users learn to avoid and deal with by terminating programs before it happens. So "running out of memory" isn't all that common a problem in a virtual memory system, and when it does happen, you are at the mercy of every component in the OS handling it gracefully. That can be an issue.
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  10. #20


    Posts : 1,925
    Windows 8.1 Pro


    Sorry, but I don't consider shutting down like that to be "graceful". For instance, you may lose your current document because memory is in an unstable state. You may not be able to open a file save dialog, or even write a dump file to disk. You can't really put a try/catch around everything that could possibly allocate some memory. It would make your code virtually unreadable, and difficult to maintain.

    And exiting with an unhandled exception is hardly graceful, even if it does clean up after itself as much as it can... Basically, most experts say it's fruitless to check most memory allocations. Yes, large allocations can be beneficial, such as knowing if you can load a large bitmap into memory... but that kind of memory failure is different from a memory exhaustion situation.
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