Interrupt 26h	Absolute Disk Write	  Interrupt 25h   Absolute Disk Read
(0:0094h, 0:0098h) 
  These transfer control directly to the device\drivers. On return, the
original flags are still on the stack (put there by the INTEL\80x86op -INT
instruction). This is necessary because return information is passed back in
the current flags.
  The number of sectors specified is transferred between the given drive and
the transfer address. Logical sector numbers are obtained by numbering each
sector sequentially starting from track 0, head 0, sector 1 (logical sector 0)
and continuing along the same head, then to the next head until the last sector
on the last head of the track is counted.  Thus, logical sector 1 is track 0,
head 0, sector 2; logical sector 2 is track 0, head 0, sector 3; and so on.
Numbering then continues wih sector 1 on head 0 of the next track. Note that
although the sectors are sequentially numbered (for example, sectors 2 and 3 on
track 0 in the example above), they may not be physically adjacent on disk, due
to interleaving. Note that the mapping is different from that used by DOS 1.10
for dual-sided diskettes.
 
Interrupt 26h	Absolute Disk Write	  Interrupt 25h   Absolute Disk Read
The request is as follows: 
 
int 25 for Absolute Disk Read, 
int 26 for Absolute Disk Write 
entry   AL      drive number (0=A:, 1=B:, etc) 
	CX      number of sectors to read 
	DS:BX   disk transfer address (buffer) 
	DX      first relative sector to read - beginning logical sector number 
return  CF      set if error 
	AL	error code issued to Int\24 in low half of DI
	AH      01h     bad command 
		02h	bad address mark
		03h     write-protected disk
		04h     requested sector not found
		08h     DMA failure 
		10h     data error (bad CRC) 
		20h     controller failed 
		40h     seek operation failed 
		80h     attachment failed to respond 
Interrupt 26h	Absolute Disk Write	  Interrupt 25h   Absolute Disk Read
note 1) Original flags on stack! Be sure to pop the stack to prevent
	uncontrolled growth 
     2) Ints 25 and 26 will try rereading a disk if they get an error the first 
	time. 
     3) All registers except the segment registers are destroyed by these calls 
 
 
Interrupt 26h   ABSOLUTE DISK WRITE 
		(except DOS 4.0/Compaq DOS 3.31 32M partition) 
entry   AL      drive number (0=A, 1=B, etc) 
	DS:BX   pointer to Disk Transfer Address (buffer) 
	CX      number of sectors to write 
	DX      first relative sector to write 
return  CF      1 if error 
                AL      error code issued to Int\24 in low half of DI
		AH      same error codes as for int 25h 
note    Original flags on stack! 
 
Interrupt 26h   DOS 4.0/Compaq DOS 3.31 - ABSOLUTE DISK WRITE 
		(32M hard disk partitions) 
entry   AL      drive number (0=A, 1=B, etc) 
	CX      0FFFFh 
	DS:BX   Packet address 
		DWORD  sector number 
		WORD   number of sectors to write 
		DWORD  transfer address 
return  same as above? 
note    Partition is potentially 32M (and requires this form of the call) if 
	bit 1 of struct -device attribute code in device\drivers are set