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AH = 53h
DS:SI -> BIOS Parameter Block (see #01663)
ES:BP -> buffer for Drive Parameter Block (see #01395 at AH=32h)
DBP drive byte must be set to valid drive (Windows95-OSR2)
---Windows95---
CX = signature 4558h ('EX') for FAT32 extended BPB/DPB (see #01664)
DX = signature 4152h ('AR') for FAT32 extended BPB/DPB
Return:
ES:BP buffer filled
Notes: For DOS 3.0+, the cluster at which to start searching is set to 0000h and the number of free clusters is set to FFFFh (unknown). If the number of sectors per cluster is set to zero, MS-DOS will hang at startup because it computes the internally-used shift count by shifting this value right until the carry flag is set; since this will never happen when the field is zero, MS-DOS hangs. Not supported by Windows NT 3.1
Format of BIOS Parameter Block: Offset Size Description (Table 01663) 00h WORD number of bytes per sector 02h BYTE number of sectors per cluster 03h WORD number of reserved sectors at start of disk 05h BYTE number of FATs 06h WORD number of entries in root directory 08h WORD total number of sectors for DOS 4.0+, set to zero if partition >32M, then set DWORD at 15h to actual number of sectors 0Ah BYTE media ID byte (see #01356) 0Bh WORD number of sectors per FAT ---DOS 2.13--- 0Dh WORD number of sectors per track 0Fh WORD number of heads 11h WORD number of hidden sectors ---DOS 3.0+ --- 0Dh WORD number of sectors per track 0Fh WORD number of heads 11h DWORD number of hidden sectors 15h 11 BYTEs reserved ---DOS 4.0+ --- 15h DWORD total number of sectors if word at 08h contains zero 19h 6 BYTEs ??? 1Fh WORD number of cylinders 21h BYTE device type 22h WORD device attributes (removable or not, etc) ---DR DOS 5+ --- 15h DWORD total number of sectors if word at 08h contains zero 19h 6 BYTEs reserved ---European MS-DOS 4.00--- 15h DWORD total number of sectors if word at 08h contains zero (however, this DOS does not actually implement >32M partitions)
See Also: #01395 - #01664
Format of Extended BIOS Parameter Block: Offset Size Description (Table 01664) 00h 25 BYTEs same as standard DOS 4-6 BPB (see #01663) 19h DWORD sectors per FAT if WORD at 0Bh is 0000h 1Dh WORD extended flags
bit 7:
Do not mirror active FAT to inactive FATsbits 6-4:
Reserved (0)bits 3-0:
The 0-based FAT number of the active FAT (if mirroring disabled) 1Fh WORD file system version (high byte=major, low byte=minor) 0000h = Win95-OSR2 21h DWORD starting cluster number of root directory 25h WORD file system information sector number (see also #01788) FFFFh if none 27h WORD sector number of backup boot sector (FFFFh if none) 29h 6 WORDs reserved
See Also: #01560 - #01787
Category: DOS Kernel - Int 21h - D
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