The Registry 3: Session Manager
Editors Note:
At the HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Control \SessionManager sub-key, you will find the global variables that are used to control sessions. In this article we are goingto look at these variables, at what they are for and what you may want to change.
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Caution: Editing the registry can be extremely dangerous and candisrupt your system to the point where your only option is to re-install Windows NT. |
Refer to the article Registry:Basics for information on safe handling of the registry.
Session Manager
When you click \Session Manager, you will see in the right half ofthe window several value entries that contain global variables. Most of these variables must be left alone, butyou can change GlobalFlag. If you have applications that can run under both OS2 and MS-DOS, they will run underOS2 if GlobalFlag is set to the default 0x21100000 or under MS-DOS if you change the value to 0x20100000.
Note that you may have another sub-key called \SessionManager, withno embedded space. Leave this one alone and just work in \Session Manager.
Session Manager Sub-Keys
There are also sub-keys under \Session Manager:
\AppPatches: This contains sub-keys whose value entries documentpatches that have been applied to various applications.
\DOS Devices: These are links that Windows NT creates at startup.You shouldnt change these.
\Environment: Paths to various subsystems such as OS2. Youcan change these if you want to move the subsystems off the system partition, but be very careful: If you misspella path, the subsystem it refers to wont run. This can be disastrous, as the value entry "Path" refersto Windows NT logon, and "windir" points to the Windows NT folder. If you get this wrong, you may haveto do a repair or re-install Windows NT. We do not recommend that you move parts of the Windows NT operating systemoff the system partition.
\Executive: These value entries are for advanced system tuningsuch as creating additional process threads. (A thread is an agent of a process, which runs program code. A processcan have several threads, so several sections of program code can be executing concurrently.) Unless you have athorough understanding of Windows NT, you should leave these alone.
\FileRenameOperations: System files that are locked cannotbe changed while Windows NT is running. However, there are ways to copy, move or rename them. When this is done,the change is not completed until the system is rebooted. The value entries at this location are used to completethe change when you reboot. There is nothing here that you will ever need to change manually.
\KnownDLLs: Dynamic Link Libraries (DLLs) are essentially subroutinesthat applications use during execution. The DLLs listed here are loaded into memory during startup, and stay there.Theoretically you could save memory by removing from this subkey any DLLs that are never used. The hard part isdetermining which DLLs, if any, are safe to take out, so dont bother; its not worth the danger. Buy more memoryif you need it, but leave these entries alone.
\SubSystems: These are paths for starting various subsystems.Its a lot like \Environment, with the major difference that these values are set during startup. If you do changea value in \Environment, the corresponding value in \Subsystem (if there is one) will be automatically set whenyou reboot. You should never need to change anything here.
\Memory Management: This is the most likely area to need tuning.Most of the value entries are maintained from Control Panel \ System \ Virtual Memory, but there are a couple youmay tweak manually.
Memory Management Value Entries
Some of these entries may not appear in your Registry. If so, youcan add them, but be sure you spell them EXACTLY as presented here, without changing the case of any character.
ClearPageFileAtShutdown: When this is set to a Value Type ofREG_DWORD and a value of 1, all data in the paging file will be cleared upon system shutdown. You must rebootfor this change to take effect. The paging file will not be cleared on this reboot, but will clear on each subsequentone.
DisablePagingExecutive: When set to zero, this allows WindowsNT to page the kernel pools to the paging file; set it to one, and the kernel pool will stay in memory. If youhave a large amount of unused memory, or if for some reason your paging file is slow, this might be of value. Disablingthe Paging Executive may slow your system to a crawl, so if you are going to try changing this, pick a time whenyour system can be out of production for a while.
IoPageLockLimit: This value is the maximum bytes of memorythat can be locked for I/O operations. A value of 0 defaults to 512 kilobytes. Raising this value can give youa significant performance boost. The procedure is detailed in the article MemoryUsage .
LargeSystemCache: 0 tells the system to favor the processesworking set, non-zero means to favor the system-cache working set. For most systems, your applications will runfaster if this value is set to zero; if it is non-zero, your paging file may be over-active (if you have a noisyhard drive, check to see if LargeSystemCache is non-zero). Most Workstations should have this set to zero and mostServers should have it set to one.
PagedPoolQuota
PagedPoolSize: There are several value entries dealing withsystem memory. They include MinimumPagedPoolSize , MaximumPagedPoolSize and others,and all of the "PagedPool" set for NonPagedPool. "Pool" is all of the system memory. "Paged"means it can be paged, or written to the disk. "NonPaged" means it cant be written to the disk. The valuesin the registry are normally zero, which tells Windows NT to calculate default values relative to the amount ofRAM on your computer. You should leave these alone, because changing these values can cause Windows NT to miscalculateother resource allocations; incorrect values can cause Windows NT to malfunction and possibly even cause file systemcorruption.
A professional who knows what side-effects will occur may benefitfrom reducing the pool allocations (setting values larger than the defaults will have no effect), but very fewpeople outside Microsoft know enough to safely tinker with this. If youre interested in the details of the defaultcalculations, see the Microsoft article Q126402 . You can find Knowledge Base articles by goingto www.microsoft.com , clicking Support in the menu bar, then clicking Support Online in the first paragraph.Click the radio button Specific article ID number then enter the article number.
PagingFiles: Data about existing paging files (location andsizes) are stored here. You should use Control Panel / System / Performance to adjust your paging files, but thisvalue can be handy if you get into trouble. For example, if your paging file is smaller than your physical memoryor your system partition does not have enough free space to record a crash dump file, then if you get a bug check(the blue screen crash), your system may go into a continuous series of reboots. The Microsoft Knowledge Base article Q174630 details how to handle this.
SecondLevelDataCache: This is the amount of L2 cache WindowsNT will use. It defaults to 0, which is the correct value for 256 kilobytes of L2 cache. If it is set to 0, butyou have more than 256 kilobytes of cache, you should change it.
- Double-click SecondLevelDataCache to bring up the DWORD Editor
- Click the Decimal radio button
- Enter the amount of L2 cache you have, such as "512" for 512 kilobytesof cache
- Click OK
This will probably give you a noticeable performance increase. Somepeople have reported no change, while others say their performance more than doubled.
SystemPages: Here you specify the number of page tableentries available. The default is almost always sufficient, but if you install a PCI card with a very large amountof on-board memory (such as a very sophisticated video card) and you cannot access all of the cards memory, thisis probably where the solution will be. Contact the cards manufacturer for the correct value to enter.
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