typedef struct _KAPC
{
     UCHAR Type;
     UCHAR SpareByte0;
     UCHAR Size;
     UCHAR SpareByte1;
     ULONG SpareLong0;
     PKTHREAD Thread;
     LIST_ENTRY ApcListEntry;
     PVOID KernelRoutine;
     PVOID RundownRoutine;
     PVOID NormalRoutine;
     PVOID NormalContext;
     PVOID SystemArgument1;
     PVOID SystemArgument2;
     CHAR ApcStateIndex;
     CHAR ApcMode;
     UCHAR Inserted;
} KAPC, *PKAPC;

Windows Vista Kernel Structures