Wiki Pages / Categories: DRDOS, DOS | Page Actions: View Edit History Print

FAT+

DRDOS DOS

FAT plus is a new standard defined by Enhanced Dr-DOS and Free-DOS developers. It extends the capacity of FAT16 (not very useful) and FAT32 partitions (very useful, called then FAT32+ and supporting files up to 256 GB).

For files larger than 4 GB, in Enhanced DR-DOS 7.01.08 WIP the file pointer can be set with the following new 64-bit DOS function, shown as a modified excerpt of Ralf Brown’s Interrupt List:

--------O-217142-------------------------------
INT 21 - Enhanced DR-DOS 7.01.08+ - "Long LSEEK" - 
SET CURRENT 64-bit FILE POSITION
	AX = 7142h
	CL = origin of move
	    00h start of file
	    01h current file position
	    02h end of file
	BX = file handle
	DS:DX = pointer to (signed) 64-bit offset from 
                origin of new position
Return: CF clear if successful
	    DS:DX unchanged, new 64-bit position from 
                  start of file written into memory at -> DS:DX
	CF set on error
	    AX = error code (01h,06h) (see #01680 at AH=59h/BX=0000h)

Note: Since sequential read/writes do not require the file pointer to be set with the LSeek function, they also can work on huge files even if the application using them is not aware of the FAT+ filesystem extension.

Documentation / Specification

If you want to develop a driver, update a kernel of DOS or just are interested you can download the documentation here: http://www.fdos.org/AutoIndex/kernel/fatplus.txt

See also: FAT & LFN

DR-DOS

DOS