2 Responses to “LargeSystemCache and DisablePagingExecutive in Registry”

1. Larry Miller says:

   May 7, 2009 at 3:46 pm

   NOT RECOMMENDED.

   Microsoft has clearly documented that this setting is for systems used primarily as servers. For Workstation use it will almost always be bad.

   By default in XP and Vista memory management parameters are set for optimum application performance. Memory for application use and for caching are dynamically balanced to this end. LargeSystemCache changes this balance to heavily favour memory for caching use, and this will often be well beyond the point where application performance is impaired. In a file server this is a good thing. A file server lives to share files to network clients and application performance is very much a secondary consideration. In this case a large cache is essential, even if applications have to be starved.

   On a workstation the priorities are very different. A large cache is good, but only if applications can still get the memory that they need. The default setting of LargeSystemCache provides this balance.

   This setting can have severe effects on some common hardware configurations. Problems range from severe performance problems, system instability, and data corruption. In some cases users have had to reinstall Windows to restore operation.

   YOU HAVE BEEN WARNED.

   This setting can be useful, but only when it is appropriate. It should only be used after careful consideration of the implications and possible risks.

   References:
   http://support.microsoft.com/kb/895932

   Larry Miller
   Microsoft MCSA

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   • Josh Silver says:

     July 6, 2009 at 7:22 pm

     I’m pretty sure that this setting only changes the amount of physical memory that the filesystem cache is allowed to occupy. That’s what Microsoft says. If it does something other than that, it’s not documented by Microsoft.

     Unless Microsoft is beating around the bush, or not revealing the entire truth in this article (http://technet.microsoft.com/en-us/library/cc784562(WS.10).aspx), then enabling LargeSystemCache on computers with a lot of RAM (at least 2 GB) should increase filesystem performance without decreasing application performance.

     In the article you linked, MS states “If you use a server product as a desktop, you should consider changing the resource allocation to Programs mode or [b]adding more physical RAM[/b].” This means that having a lot of RAM is an alternative to disabling LargeSystemCache.

     MS also states in the article you linked, that “If performance improves by switching from System cache mode to Programs mode, the operating system is being presented with a [b]low memory resource condition[/b].” If we look at the meaning of that quote, it means that if performance [b]decreases[/b] by switching from System Cache mode to Programs mode, the OS is being presented with a [b]lot of memory[/b]. Meaning that enabling LargeSystemCache only decreases performance on systems using low memory, and increases performance on systems with a lot of memory.

     Again, from my own experience, 2 GB or more is necessary to facilitate a LargeSystemCache, but every machine varies on how much RAM they use, depending on their setup and the applications they use.

     There is a simple way to find out if this setting is right for your particular computer. In task manager, under the “Performance” tab and in the “Commit Charge (K)” category, is the label “Peak” with a bunch of numbers to the right of it. This peak, is the largest amount of both virtual and physical memory that has been used at any point in time during the current Windows session. Divide the number by 1024 to get the peak in megabytes. To the top right under “Physical Memory (K)” is the label “Total”, which is the total amount of RAM installed in the system. Again, divide by 1024 to get the total in MB.

     If the Peak stays below the amount of physical memory while LargeSystemCache is enabled, you’re good to go. You will get increased performance because more of your RAM is being used. However, if the Peak grows as large as the amount of the “Total” of physical memory installed in the system when large cache is enabled, then you do not have enough memory to facilitate a large system cache, and memory is being paged to the hard disk drive. This will decrease performance. If this happens even when you don’t have LargeSystemCache enabled, it goes without saying that you need more RAM, because virtual memory is slow. Also, make sure to measure the peak after doing everything you normally do on your computer. If you want, you could regularly check the peak, just to make sure you have available RAM.

     So that’s the explanation of the benefit of this registry tweak. Thanks for the warning, Larry Miller, but you should include that the warning only applies to systems with not enough RAM installed. However I don’t think you actually knew what this setting does. You can see that limiting the system cache by default for workstations, especially at a time when most computers had around 512 MB or less, was a good idea for practically every computer around. However, times have changed, and a lot of people have 2 GB or more.

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