The SYSTEM_DEVICE_INFORMATION structure is what a successful call to ZwQuerySystemInformation or NtQuerySystemInformation produces in its output buffer when given the information class SystemDeviceInformation (0x07).

Documentation Status

The SYSTEM_DEVICE_INFORMATION structure is not documented.

A comment in NTDDK.H says of the documented CONFIGURATION_INFORMATION structure that “it is used by the NtQuerySystemInformation system service to return device type counts.” Be aware that “used by” would seem to mean only that a CONFIGURATION_INFORMATION in the kernel provides the data that gets returned, not that the data is returned as a CONFIGURATION_INFORMATION.

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_DEVICE_INFORMATION is 0x18 bytes in both 32-bit and 64-bit Windows.

Offset Definition
ULONG NumberOfDisks;
ULONG NumberOfFloppies;
ULONG NumberOfCdRoms;
ULONG NumberOfTapes;
ULONG NumberOfSerialPorts;
ULONG NumberOfParallelPorts;