Figure 1 The set of parameters contained in DISK_BASE are used by the BIOS for normal diskette operations. This paramater block is pointed to by the BIOS variable DISK_POINTER located at 0000:0078, which is equivalent to the address of interrupt 1EH. This pointer value can be redirected to point to a new set of parameters thus allowing the PC to access non DOS type formats.

DISK_BASE:
     DB  11001111B  ;SRT=C, HD UNLOAD=F
     DB  2          ;HEAD LOAD=1,MODE=DMA
     DB  37         ;WAIT AFTER OPERATION UNTIL
                    ;MOTOR TURNS OFF
     DB  2          ;CODE FOR 512 BYTES/SECTOR
                    ;1=256,2=512,3=1024 ETC
     DB  9          ;LAST SECTOR ON TRACK
     DB  2AH        ;GPL IS GAP3 LENGTH FOR DATA
                    ;READ AND DETERMINES HOW LONG
                    ;VCO WILL 'IDLE'. MUST BE
                    ;ADJUSTED.
     DB  OFFH       ;DATA LENGTH, LEAVE AT OFFH
     DB  50H        ;GAP3 LENGTH FOR FORMAT COMMAND
                    ;MUST BE ADJUSTED FOR SOME
                    ;DISK FORMATS.
     DB  OF6H       ;FORMAT FILLER BYTE. CAN BE
                    ;ALTERED IF REQUIRED.
     DB  25         ;HEAD SETTLING TIME (MILLI SECONDS)
     DB  4          ;MOTOR START TIME (1/8 SECONDS)