Int 13 Fn 25  - Hard Disk - Ps/1 And Newer Ps/2 - Identify Drive           [d]

   AH = 25h
   DL = drive number (80h,81h)
   ES:BX-> 512 byte buffer for reply packet

Return: CF clear if successful
   CF set on error
   AH = status (see #0166 at AH=01h)
   buffer filled with ATA/IDE-style drive information block (see #0199)
Desc:  retrieves the 256 words of drive data stored on an IDE hard disk

Notes: the byte at address 0040h:0074h is set to the status of the operation
   IBM officially classifies this function as optional

See Also: AH=23h"PS/1"

Format of drive information block:
Offset Size    Description (Table 0199)
 00h   WORD    general drive configuration (see #0200)
 02h   WORD    number of cylinders
 04h   WORD    reserved
 06h   WORD    number of heads
 08h   WORD    number of unformatted bytes per track
 0Ah   WORD    number of unformatted bytes per sector
 0Ch   WORD    number of sectors per track
 0Eh  6 BYTEs  vendor unique
 14h 20 BYTEs  serial number in ASCII, 0000h=not specified)
 28h   WORD    buffer type
 2Ah   WORD    buffer size in 512 byte increments (0000h=not specified)
 2Ch   WORD    number of ECC bytes passed on Read/Write Long cmds
       0000h = not specified
 2Eh  8 BYTEs  firmware revision in ASCII, 0000h=not specified
 36h 40 BYTEs  model number in ASCII, 0000h=not specified
 5Eh   WORD    bits 15-8  Vendor Unique
       bits 7-0  00h = Read/Write Multiple commands not implemented
             xxh = Maximum number of sectors that can be
             transferred per interrupt on Read and Write
             Multiple commands
 60h   WORD    0000h = cannot perform doubleword I/O
       0001h = can perform doubleword I/O
 62h   WORD    capabilities
       bit 15-9  0=reserved
       bit 8  1=DMA Supported
       bit 7-0  Vendor Unique
 64h   WORD    reserved
 66h   WORD    bits 15-8 PIO data transfer cycle timing mode
       bits 7-0  Vendor Unique
 68h   WORD    bits 15-8 DMA data transfer cycle timing mode
       bits 7-0  Vendor Unique
 6Ah   WORD    bits 15-1 reserved
       bit 0   1=the fields reported in tranlation mode are valid
           0=the fields reported in translation mode may be valid
 6Ch   WORD    number of current cylinders
 6Eh   WORD    number of current heads
 70h   WORD    number of current sectors per track
 72h   DWORD   current capacity in sectors
 76h   WORD    reserved
 78h 136 BYTEs not defined by ATA spec 2.6
100h 64 BYTEs  vendor unique
140h 96 BYTEs  reserved

Note:  the above description is as in the ATA (AT Attachment) Specification.

See Also: #P157

Bitfields for general drive configuration:
Bit(s) Description (Table 0200)
 15    0   reserved for non-magnetic drives
 14    format speed tolerance gap required
 13    track offset option available
 12    data strobe offset option available
 11    rotational speed tolerance is > 0.5%
 10    disk transfer rate > 10 Mbs
 9 disk transfer rate > 5Mbs but <= 10Mbs
 8 disk transfer rate <= 5Mbs
 7 removable cartridge drive
 6 fixed drive
 5 spindle motor control option implemented
 4 head switch time > 15 usec
 3 not MFM encoded
 2 soft sectored
 1 hard sectored
 0 reserved (0)