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Windows | Windows - Low On Registry Space

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Contents of this article

Not the solution: RegistrySizeLimit
Observations
The Solution - or: The Workaround
Variant A
Variant B

[inturl=./upload/files/1_unbenanntxp.png][imgleft=The error message under XP]./upload/files/thumbs/1_unbenanntxp.png.jpg[/imgleft][/inturl] I've been bothered by the error "Low On Registry Space - The system has reached the maximum size allowed for the system part of the registry. Additional storage requests will be ignored." more frequently lately on various Windows XP machines. If you believe the error, changes to the registry are no longer being saved, which is obviously bad.
[aname=heading-1][/aname][h3]Not the solution: RegistrySizeLimit[/h3]
The internet quickly jumped on the registry value [highlight]RegistrySizeLimit[/highlight], claiming that having it set incorrectly or not at all is the solution to the error, but that is wrong. The registry value [url=https://web.archive.org/web/20080121131118/http://support.microsoft.com/kb/124594/de]is only relevant for NT 4.0 and Windows 2000[/url] and no longer applies to Windows XP and later. The Microsoft explanation pages regarding [url=https://learn.microsoft.com/de-at/windows/win32/sysinfo/registry-storage-space]Registry Storage Space[/url] and [url=https://learn.microsoft.com/de-at/troubleshoot/windows-server/performance/unable-allocate-memory-system-paged-pool]PagedPoolSize[/url] are also not particularly helpful. Defragmenting the registry via [url=https://www.majorgeeks.com/files/details/ntregopt.html]NTREGOPT[/url] didn't yield any results (at least for me) either.
[aname=heading-2][/aname][h3]Observations[/h3]
Everyone likely knows that Windows XP stores the registry in [highlight]C:\WINDOWS\SYSTEM32\CONFIG[/highlight], which can be edited with [highlight]REGEDIT.EXE[/highlight]. Here I noticed that the file [highlight]SYSTEM[/highlight] was coincidentally exactly 8192 KB, or to be precise 8 MB, in size. That smelled to me like a hard limit... but well, how do you make it smaller?
[aname=heading-3][/aname][h3]The Solution - or: The Workaround[/h3]
My XP installation originally comes from a VirtualBox installation where I patched it with POSReady updates, pre-installed all C++ and .NET libraries, etc., and I've been using this image on every PC I want to install XP on ever since. It should be noted: It doesn't really matter if the installation comes from VirtualBox; it could come from any other PC (e.g., a hardware swap without reinstalling XP).

Windows XP stores the hardware configuration under [highlight]HKLM\System\CurrentControlSet\Enum[/highlight] and its subfolders, and additionally clones the configuration to [highlight]HKLM\System\ControlSet00x[/highlight] ([highlight]1[/highlight] failed, [highlight]2[/highlight] Last Known Good Configuration in the F8 boot menu, and [highlight]3[/highlight] currently used profile - the mapping may vary, see [highlight]HKLM\System\Select[/highlight]).

[inturl=./upload/files/1_unbenanntxp2.png][imgright=Problem solved]./upload/files/thumbs/1_unbenanntxp2.png.jpg[/imgright][/inturl]Every device that was ever detected is stored in this registry area, bloating it with useless data that is never deleted. Consequently, a complete hardware change - by deploying the VirtualBox image to a real and completely different PC - fills the registry section with an unusually large amount of useless hardware information.
[aname=heading-4][/aname][h4]Variant A[/h4]
I went through all [highlight]ENUM[/highlight] subkeys under [highlight]CurrentControlSet[/highlight] and deleted every entry that was unrelated to the hardware my current installation is running on.
[aname=heading-5][/aname][h4]Variant B[/h4]
Did you know that Device Manager still does not show all devices even when you select "View" -> "Show hidden devices" - especially those originating from a different hardware configuration? To make it display every device stored in the registry, create a .BAT file with the following contents:
[highlight]set DEVMGR_SHOW_DETAILS=1
set DEVMGR_SHOW_NONPRESENT_DEVICES=1
start devmgmt.msc[/highlight]
After running the .BAT file, selecting "View" -> "Show hidden devices" will now actually display every device Windows has ever detected. Then uninstall every semi-transparent device by right-clicking it. Once that is done, restart the computer.
[aname=heading-6][/aname][h4]After completing Variant A or B[/h4]
Once Windows has booted again, open Registry Editor and navigate to [highlight]HKLM\System[/highlight]. Take ownership of the "ControlSet001", "ControlSet002", and "ControlSet003" keys (not all of them may exist) by right-clicking them, selecting "Permissions...", and granting yourself Full Control. However, do this only for those ControlSets that are not defined as "Current" or "Default" under [highlight]HKLM\System\Select[/highlight] (this is usually ControlSet001). Then simply delete the entire key/branch. After another reboot, Windows will automatically recreate a copy of [highlight]CurrentControlSet[/highlight] as "ControlSet002" (assuming ControlSet001 is Current/Default) and assign it as the "Last Known Good Configuration" for the F8 boot menu ("LastKnownGood" in the "Select" key). This time, however, it will be based on the already cleaned-up Device Manager and will therefore be significantly leaner.

Voila, the problem is gone permanently. And the [highlight]SYSTEM[/highlight] file in [highlight]C:\WINDOWS\SYSTEM32\CONFIG[/highlight] has shrunk from 8192 kB (exactly 8 MB) to 5632 kB.
[aname=heading-7][/aname][h3]But why exactly 8 MB?[/h3]
I never fully understood it, but it is a limitation dating back to the early days of Windows NT, where the size of the paging file and the registry could grow proportionally based on the amount of physical RAM, and the registry did so in a way that could reach its limits rather quickly. During my research, I only found [url=https://ftp.zx.net.nz/pub/archive/ftp.microsoft.com/MISC/KB/en-us/292/726.HTM]this old KB article[/url], which states the following:
[quote=KB292726]In Windows Server 2003 and Windows XP, there is no longer a paged-pool-based size limitation for the registry. The registry files are now mapped into the system cache address space through memory mappings. Therefore, regardless of the actual size of a hive, a maximum of 4 megabytes (MB) of memory is charged for it. Note: On Windows Server 2003, the System hive is limited to 12 MB when the /3GB switch is used.[/quote]
At this point, I stopped looking for a deeper explanation, because my workaround had already solved the problem for me. The fact that I get sunburned when exposed to too much sunlight is an unchangeable fact. Even if I understand the biological causes down to the smallest detail, it does not change the outcome. The same applies here: Windows has a fixed limit and once you reach it, you have to take care, but you cannot increase the limit itself.

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Beitrag (ID: 169) von freaked 179 Klicks | Quelle
Geschrieben: 09.03.2026, 20:01:56 Uhr
Überarbeitet: 21.07.2026, 10:15:28 Uhr

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