Format of Overlay Asynchronous Control Block (OACB): Offset Size Description ) 00h DWORD link to next OACB, 0000h:0000h if last (filled by VLM.EXE) 04h DWORD callback address or 0000h:0000h 08h BYTE InUse flag (00h if complete) (set by VLM.EXE) 09h BYTE flag, reserved for VLM use 0Ah WORD destination VLM 0Ch WORD destination function 0Eh WORD temporary storage for VLM.EXE 10h 6 BYTEs reserved 16h 6 DWORDs EAX,EBX,ECX,EDX,ESI,EDI 2Eh 4 WORDs DS,ES,FS,GS (FS and GS not used)