typedef struct _KPCR
{
     union
     {
          NT_TIB NtTib;
          struct
          {
               PEXCEPTION_REGISTRATION_RECORD Used_ExceptionList;
               PVOID Used_StackBase;
               PVOID Spare2;
               PVOID TssCopy;
               ULONG ContextSwitches;
               ULONG SetMemberCopy;
               PVOID Used_Self;
          };
     };
     PKPCR SelfPcr;
     PKPRCB Prcb;
     UCHAR Irql;
     ULONG IRR;
     ULONG IrrActive;
     ULONG IDR;
     PVOID KdVersionBlock;
     PKIDTENTRY IDT;
     PKGDTENTRY GDT;
     PKTSS TSS;
     WORD MajorVersion;
     WORD MinorVersion;
     ULONG SetMember;
     ULONG StallScaleFactor;
     UCHAR SpareUnused;
     UCHAR Number;
     UCHAR Spare0;
     UCHAR SecondLevelCacheAssociativity;
     ULONG VdmAlert;
     ULONG KernelReserved[14];
     ULONG SecondLevelCacheSize;
     ULONG HalReserved[16];
     ULONG InterruptMode;
     UCHAR Spare1;
     ULONG KernelReserved2[17];
     KPRCB PrcbData;
} KPCR, *PKPCR;

Windows Vista Kernel Structures