The SYSTEM_FILECACHE_INFORMATION structure is produced as output by the functions ZwQuerySystemInformation or NtQuerySystemInformation when given any of the information classes

The first two are also acceptable as input to the functions ZwSetSystemInformation or NtSetSystemInformation.

The information classes select different Working Sets to operate on: the System Cache for the first two, the Paged Pool and the System PTEs for the second two.

Documentation Status

The SYSTEM_FILECACHE_INFORMATION structure is not documented.

Microsoft does publish the practical equivalent of a C-language definition as type information in public symbol files, though not for the kernel, where the structure is prepared, nor even for low-level user-mode DLLs that interpret the structure, but for various higher-level user-mode DLLs such as URLMON.DLL and only then starting with version 6.2.

Two earlier disclosures of type information are known, though not in symbol files but in statically linked libraries: GDISRVL.LIB from the Device Driver Kit (DDK) for Windows NT 3.51; and SHELL32.LIB from the DDK for Windows NT 4.0.


The SYSTEM_FILECACHE_INFORMATION is 0x24 or 0x40 bytes in 32-bit and 64-bit Windows, respectively, in version 4.0 and higher. It is originally only 0x0C bytes.

Offset (x86) Offset (x64) Definition Versions
0x00 0x00
ULONG_PTR CurrentSize;
0x04 0x08
0x08 0x10
ULONG PageFaultCount;
0x0C 0x18
ULONG_PTR MinimumWorkingSet;
4.0 and higher
0x10 0x20
ULONG_PTR MaximumWorkingSet;
4.0 and higher
0x14 0x28
ULONG_PTR CurrentSizeIncludingTransitionInPages;
4.0 and higher
0x18 0x30
ULONG_PTR PeakSizeIncludingTransitionInPages;
4.0 and higher
0x1C 0x38
ULONG TransitionRePurposeCount;
4.0 and higher
0x20 0x3C
ULONG Flags;
4.0 and higher

When this structure is used for setting system information, only MinimumWorkingSet, MaximumWorkingSet and Flags matter. The Flags matter only for SystemFileCacheInformationEx. For SystemFileCacheInformation, the Flags are treated as zero. The valid bits in the Flags are defined in WINNT.H and are documented for SetProcessWorkingSetSizeEx:

Mask Symbolic Name