| Format of DOS/16M XBRK structure | 
| Offset | Size | Description | 
|---|---|---|
| 00h | DWORD | linear address of first available byte | 
| 04h | DWORD | linear address of last available byte + 1 ??? | 
| 08h | DWORD | real-mode address of XBRK structure??? | 
| 0Ch | DWORD | ??? | 
| 10h | 2 BYTEs | ??? | 
| 12h | WORD | segment of ??? | 
| 14h | 8 BYTEs | ??? | 
| 1Ch | 512 BYTEs | protected-mode IDT | 
| 21Ch | N BYTEs | protected-mode GDT |