INT 21 U - PTS-DOS 6.51 & S/DOS 1.0 - DIRECT DISK READ AH = 90h CX = FFFFh (for partitions > 32 Mb) DS:BX -> request block (see #04094) CX = sector count (for partitions < 32 Mb) DX = starting sector number DS:BX -> buffer Return: CF set on error AX error code CF clear on success Notes: This function is supported by Paragon Technology Systems S/DOS 1.0 (and most probably by PTS-DOS 6.51, maybe even earlier). To access big partitions (> 32 Mb), the CX != FFFFh is not allowed and the buffer must always be used. Otherwise, the system will return error code 0207h. It is currently unknown if this function is also supported by PhysTechSoft PTS-DOS 6.60, 6.70, or 2000. SeeAlso: INT 21/AH=91h"PTS",INT 25h,INT 26h Format of PTS-DOS & S/DOS disk read/write request block: Offset Size Description (Table 04094) 00h DWORDDoubleword; four bytes. Commonly used to hold a 32-bit segment:offset or selector:offset address. sector number 04h WORD counter 06h DWORDDoubleword; four bytes. Commonly used to hold a 32-bit segment:offset or selector:offset address. pointer to buffer