SYSTEM_INTERRUPT_INFORMATION

The SYSTEM_INTERRUPT_INFORMATION structure is produced in the output buffer by a successful call to the following functions:

when given the information class SystemInterruptInformation (0x17).

Documentation Status

The SYSTEM_INTERRUPT_INFORMATION structure is defined in WINTERNL.H from the Software Development Kit (SDK). The definition there has the whole structure as one array of bytes, named Reserved1. Documentation of NtQuerySystemInformation describes the structure as “opaque” and suggests that whatever is produced in it for the SystemInterruptInformation case “can be used to generate an unpredictable seed for a random number generator.”

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.

Layout

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

Offset Definition
0x00
ULONG ContextSwitches;
0x04
ULONG DpcCount;
0x08
ULONG DpcRate;
0x0C
ULONG TimeIncrement;
0x10
ULONG DpcBypassCount;
0x14
ULONG ApcBypassCount;