From: "Matthias Paul" <PAUL-MA AT reze-1 DOT rz DOT rwth-aachen DOT de>
Organization:  Rechenzentrum RWTH Aachen
To: opendos AT delorie DOT com
Date:          Tue, 7 Nov 2000 18:11:30 +0100
Subject:       OEM label info
X-mailer: Pegasus Mail v3.22
Message-ID: <6B2A6BB4B74@reze-1.rz.rwth-aachen.de>
Reply-To: opendos AT delorie DOT com

Hi all,

Now that the signal-to-noise-ratio has hopefully again become 
positive, I hope that this info may help those who are still 
interested in technical and DOS related details and who may 
wish to further investigate the "FDISK problem". 

This is partially based on a post I made back on 2000-03-14
and stuff I sent to Ralf for inclusion in INTER61 (and will
probably show up with INTER62). BTW. Ralf Brown's Interrupt 
List INTER61 (FreeDOS people call it RBIL) can be found at 

 http://www.cs.cmu.edu/afs/cs/user/ralf/pub/WWW/files.html

Please send any additions and corrections to me (or directly
to Ralf, if you like).

Format of a DOS 2.0+ boot sector:
 00h   3 BYTEs   Jump to the bootstrap loader
 03h   var       BPB or extended BPB depending on OS version and 
                 filesystem
       var       bootstrap loader
 1FDh  BYTE      (DOS 3.3, Compaq DOS 3.31 and DR DOS 5.0-7.03 FDISK) 
                 boot unit

Format of a DOS FAT12/FAT16 boot sector:
  Offset    Size    Description
   00h    3 BYTEs   Jump to the bootstrap loader
                    DOS checks the first byte to be either E9h (JMP 
                    NEAR) or EBh (JMP SHORT). In the second case the 
                    3rd byte is checked to be 90h (NOP).
                    The DR DOS family additionally allows a first 
                    byte of 69h.
                    --- BPB---
   03h    8 BYTEs   OEM ID either indicating the OS or the formatter
                    Note: The correct format of the OEM string is 5 
                    chars "abcde" description plus "x.y" version 
                    number.
                    While the OEM string is don't care for any OS of 
                    the DR DOS family, the version number in the OEM 
                    ID is (undocumented) *not* don't care for MS-
                    DOS/PC DOS and OS/2 (probably also not for NT), 
                    as depending on the version number these OSes 
                    decide how to interpret the remainder of 
                    the BPB, and which entries to trust.
                    Changing this to values not recognized by these OS
                    may cause serious malfunctioning under MS-DOS/
                    PC DOS and OS/2.

                    Examples:

                    - OS/2 Warp 3 cannot access hard disk partitions 
                      formatted and/or SYSed under Novell DOS 7 - 
                      DR-DOS 7.03, while it has no problems to access 
                      DR DOS 6.0 partitions, which used "IBM  3.3". 
                      The reason is simply, that Novell DOS 7 uses
                      "NWDOS7.0" as OEM label causing OS/2 to 
                      interpret the BPB in the DOS 4.0+ style, not 
                      the Compaq DOS 3.31 style. Changing the label 
                      to "IBM  3.3" will fix the problem.
                      Note, that this is not a DR-DOS bug, as the BPB 
                      is properly filled out with the correct values.
                      TODO: Test with OS/2 Warp 4!!!

                    - MS-DOS 6.22 can seriously corrupt FAT16 
                      partitions < 128 Mb when created by DR-DOS 
                      7.02/7.03 FDISK 2.00-2.14, as they assign a 
                      "non-standard" cluster size (4 Kb instead of 2 
                      Kb). Just changing the OEM label to "IBM  3.3", 
                      without modifying the cluster size etc.
                      fixes the problem. Apparently MS-DOS does not 
                      use the cluster size value in the BPB when it 
                      does recognize the OEM label, and its own 
                      calculations based on the other values are 
                      wrong.
                      Also, this is not a DR-DOS FDISK bug, as the 
                      BPB is filled out correctly for this kind of 
                      partition.

                    - MS-DOS 7 / Windows 98 can no longer log-in 
                      floppies formatted under DR DOS when the OEM 
                      label is in an incompatible format like 
                      "?????IHC", as apparently modified to by some 
                      unknown anti-virus protection.
                      Instead it displays "Sector not found" etc. 
                      error messages. Such floppies are still 
                      readable without any problems under DR-DOS, and 
                      SCANDISK, CHKDSK, etc. cannot find any problems 
                      as there are none!
                      Changing this back to "IBM  3.3" or "DRDOS702" 
                      will fix the problem.
 
                    Known OEM strings:
                    
                    "MSDOS2.0"
                    "MSDOS3.1" MS-DOS 3.1
                    "MSDOS3.3" MS-DOS 3.3
                    "MSDOS4.0" MS-DOS 4.01
                    "MSDOS5.0" MS-DOS 5.0 - 6.22
                               Note: PC Tools DISKFIX has a bug when 
                               the version number in the OEM label is 
                               greater than 5.0.
                    "MSWIN4.0" Windows 95 (and Windows NT 4 
                               FlexBoot???)
                    "MSWIN4.1" Windows 95 OSR 2 - Windows 98 SE
                    "IBM  3.0" PC DOS 3.0
                               Note: Reportedly the PC DOS 3.0 SYS 
                               utility erroneously created BPBs that 
                               were starting at offset +02h of the 
                               boot sector due to a *short* jump at 
                               offset +00h.
                    "IBM  3.1" PC DOS 3.1
                    "IBM  3.2" PC DOS 3.2
                    "IBM  3.3" PC DOS 3.3, DR DOS 5.0 - 6.0,
                               and FDISK of Novell DOS 7, OpenDOS 
                               7.01, DR-OpenDOS 7.02, DR-DOS 7.02
                    "IBM  5.0" PC DOS 5.0, Compaq MS-DOS 5.0
                    "IBM  6.0" PC DOS 6.1
                    "IBM  7.0" PC DOS 7
                    "IBM 10.0" OS/2 1.0
                    "IBM 20.0" OS/2 2.0
                    "DIGITAL " DOS Plus 1.2 - DR DOS 5.0 "Leopard" 
                               BETA 3
                    "NWDOS7.0" Novell DOS 7 FORMAT & SYS
                               Note: The BPB usage for this kind of 
                               boot sector is identical to the DR DOS 
                               "IBM  3.3" style.
                    "OPENDOS7" OpenDOS 7.01 FORMAT & SYS
                               Note: The BPB usage for this kind of 
                               boot sector is identical to the DR DOS 
                               "IBM  3.3" style.
                    "DRDOS702" DR-OpenDOS 7.02 FORMAT & SYS
                               Note: The BPB usage for this kind of 
                               boot sectors is identical to the 
                               DR DOS "IBM  3.3" style.
                    "DRDOS  7" DR-DOS 7.02 FORMAT & SYS, DR-DOS 7.03
                               Note: The BPB usage for this kind of 
                               boot sectors is identical to the 
                               DR DOS "IBM  3.3" style.
                    "DRDOS7.X" DR-DOS 7.02 - DR-DOS 7.03 FDISK for 
                               FAT32
                    "PARAGON!" Paragon Technology Systems PTS-DOS 
                               6.51 SYS
                               also: Paragons' PTS-DOS 2000 (SYS.COM/
                               SYSFAT32.COM) for FAT12/16/32
                    "DOSBOOT"  Paragon Technology Systems PTS-DOS 
                               6.51 FORMAT
                    "PTSDOS60" PhysTechSoft PTS-DOS 6.60 (SYS), 6.70, 
                               2000
                    "PTS 6.60" PhysTechSoft PTS-DOS 6.60 FORMAT
                    "PTSDOS70" PhysTechSoft's PTS-DOS 7 BETA 1 (1995)
                    "DLDOS622" Datalight ROM-DOS 6.22 FAT12/FAT16
                    "DLDOS710" Datalight ROM-DOS 7.10??? FAT32
                               (disabled in ROM-DOS 6.22 SYS)
                    "RxDOS6.0" RxDOS 6.0
                    "RxDOS7.2" RxDOS 7.2
                    "?????IHC" anti-virus-protection???
                               Note: This signature was seen in many 
                               boot images from various sources, 
                               including from major companies like 
                               DeLL.
                               This signature was also seen created 
                               when under Windows 98 a floppy was 
                               accessed in a drive (even a "DIR 
                               A:" was sufficient!!!).
                               The "IHC" was always the same, the 
                               "?????" appears to be a random binary 
                               code, changing every time. The machine 
                               had an ASUS MB with ALI chipset, Award-
                               BIOS 4.51PG, and "ChipAwayVirus",
                               but the observed modification only 
                               happened under the GUI, not on plain 
                               MS-DOS 7.10 or DR-DOS.
                          BUG: Since the version number in the OEM 
                               label gets overwritten, this will make 
                               DR-DOS floppies unreadable under 
                               MS-DOS and Windows 9x, since
                               for compatibility reasons even the 
                               DR-DOS 7.03 BPB still uses the hidden 
                               sectors field in Compaq DOS 3.31 
                               style. This is no problem, and
                               the floppies are still accessable 
                               under DR-DOS but MS-DOS needs the OEM 
                               string to decide how to interpret the 
                               remainder of the BPB, and as the OEM 
                               string gets overwritten, MS-DOS can   
                               no longer properly log-in such 
                               floppies. The workaround is to 
                               change the OEM label back to
                               "IBM  3.3" using a disk editor.
                               BTW. This problem does not show with 
                               media formatted with "non-standard" 
                               OEM labels (e.g. fresh pre-formatted 
                               floppies out of the box, or formatted 
                               under other DOSes with "non-standard" 
                               OEM labels) simply because the other 
                               BPB entries are 100% MS-DOS 4.00+
                               compatible, while the DR-DOS entries 
                               are still 3.31.

    0Bh      WORD    Bytes per sector (usually 512)
    0Dh      BYTE    Sectors per Cluster
    0Eh      WORD    Reserved sectors at beginning (normally 1, the 
                     boot sector). The FAT area begins after the 
                     reserved sectors.
    10h      BYTE    FAT copies (normally 2)
    11h      WORD    Root directory entries: This is normally 512. 
                     This shows the maximum number of files and 
                     directories that root directory can hold. This 
                     is because the root directory has a constant 
                     length (512 entries * 32 bytes/entry /           
                     512 bytes/sector = 32 sectors)
    13h      WORD    Total sectors on disk (small): If we have less 
                     than 65536 sectors in the partition, this value 
                     contains the number. If it's more, then the 
                     number is stored in bytes 20h- 23h.
                     This is an entry that was left from the old DOS 
                     versions, when partitions could have up to 65536 
                     sectors.
    15h      BYTE    Media descriptor byte: This byte is always F8h 
                     for hard disks.
    16h      WORD    Sectors per FAT: This shows how many sectors 
                     does each FAT take up. This depends on how many 
                     clusters the partition has, and what is the FAT 
                     type (12bit/16bit).
                     This can be from 1 to 255 sectors.
                     Note: MS-DOS has a bug when setting this to 256 
                     sectors!!!
    18h      WORD    Sectors per track: Same as the physical disk's 
                     sectors per track value.
    1Ah      WORD    Sides: Same as the physical disk's head number.
    ---DOS 2.0???---
    1Ch      WORD    hidden sectors
       end of structure???
    ---DOS 3.0+???---
    1Ch      DWORD   Special hidden sectors: This is how many sectors 
                     exist between the partition's description sector 
                     and the boot sector. Usually one track.
                     Note: If not using 32-bit calculation, the high 
                     byte of this entry must be zero.
    20h      DWORD   Big total number of sectors: If we have more 
                     than 65536 sectors in the partition, their 
                     number is written here.
                     Note: If not using 32-bit calculation, this entry
                     must be zero.
    ---DOS 5.0+ extended parameter block in boot sector---
    24h      WORD    Physical drive number: This is the physical 
                     drive number (c: 80h, d: 81h etc.). 
          or BYTE    drive unit
             BYTE    reserved
    26h      BYTE    Extended boot record signature: This marks an 
                     extended boot record. If it is 29h, the disk was 
                     formatted by DOS 4.0+??? 5.0???
    27h      DWORD   Volume serial number
    2Bh   11 BYTEs   Volume label
                     "NO NAME    "
                     Sometimes also: (PTS-DOS) "NO LABEL   "
    36h    8 BYTEs   FS ID: "FAT12   ", "FAT16   ", "UNKNOWN ".
    Bootstrap loader starts approximately here...
BUGS: Under PC DOS 3.30 the total number of sectors and the big 
       total number of sectors can sometimes both be zero (due to 
       OS/2 SETUP???). If MS-DOS/PC DOS IO.SYS/IBMBIO.COM 
       detects such boot sectors it uses the value from the 
       partition record rather than the boot sector.
      The PC DOS 3.3 FDISK and OS/2 1.0 FDISK had a bug where they
       calculated a maximum number of sectors for a drive (total 
       sectors + hidden sectors) to be 10000h, while the 
       PC DOS 3.3 IBMBIO.COM can only handle a maximum of 
       FFFFh. If later issues of PC DOS/MS-DOS detect this, 
       they decrement the total number of sectors by 1.

DR DOS 5.0 - 7.03 FORMAT/SYS FAT12/FAT16 extended boot sector 
parameter table:

   00-3Dh same as for DOS 5.0+
    3Eh      WORD    physical sectors per cluster (a 512 bytes)
    40h      WORD    target load offset (0000h)
    42h      WORD    target load segment (0070h) (can be patched)
    44h      WORD    last cluster value (FFFFh)
    46h   12 BYTEs   boot file name ("IBMBIO  COM",0)
    52h      WORD    location where BIOS expects directory segment 
                     (0050h)
    54h      WORD    FAT buffer segment low (0800h)
    56h      WORD    FAT buffer segment high (1800h)
Note: The DR DOS boot sector reads in the whole boot file (up to 29 
       Kb), which can be physically located anywhere on disk as 
       long as the file is listed in the root of the drive (and 
       the drive has no more than 512 root dir entries) and it 
       does not need to be stored continously. Hence it is 
       possible to update the system files with the standard COPY
       command. The boot sector also allows to boot off logical-
       sectored media with 1 Kb sectors, e.g. Wyse partitions, 
       and copes with root directoriess that aren't an exact 
       fit with sectors.

DR DOS 5.0 - 7.03 FDISK FAT12/FAT16 extended boot sector 
parameter table:

   00h..23h same as for DOS 3.3
     24h     WORD    physical sectors per cluster (a 512 bytes)
     26h     BYTE    number of sectors in image
     27h     BYTE    reserved
     28h     WORD    target load offset (0000h)
     2Ah     WORD    target load segment (0070h) (can be patched)
     2Ch     WORD    last cluster value (FFFFh)
     2Eh  12 BYTEs   boot file name ("IBMBIO  COM",0)
     3Ah     WORD    location where BIOS expects directory segment 
                     (0050h)
     3Ch     WORD    FAT buffer segment low (0800h)
     3Eh     WORD    FAT buffer segment high (1800h)
     40h     BYTE    count of allowed retries when reading sectors 
                     (10)
                     ---optional---
     41h     BYTE    reserved / count of sectors to read (1)
     ...
    1FDh     BYTE    physical boot drive unit (also used by Compaq 
                     DOS 3.31 and DOS 3.3)
Note: The DR DOS boot sector reads in the whole boot file (up to 29 
       Kb), which can be physically located anywhere on disk as 
       long as the file is in listed in the root of the drive 
       (and the drive has no more than 512 root dir entries) 
       and does not need to be stored continous. Hence
       it is possible to update the system files with the standard 
       COPY command. The boot sector also allows to boot off 
       logical-sectored media with 1 Kb sectors, e.g. Wyse 
       partitions, and copes with root directors that aren't an 
       exact fit with sectors.

######################################################################

It is actually nothing more than switching the OEM label xxxxxyyy 
in FDISK, FORMAT, and SYS back to "IBM  3.3" instead of "DRDOS 7" / 
"DRDOS702". Of course, you can do the same using DISKEDIT or DEBUG. 
This also fixes serious OS/2 problems to access DR-DOS partitions. 
As far as I have tracked this down, the problem was not the xxxxx 
string (like "MSDOS", "MSWIN", "IBM  ", "DIGITAL", or "DRDOS"), but 
the yyy number (usually in the format y.y):

MS-DOS, PC DOS and OS/2 use it to switch between various historic 
forms how to use the entries in the BPB table at the beginning of 
the boot sector.
For compatibility with Compaq DOS 3.31 and older issues of DR DOS,
DR-DOS 7 still uses the entry for hidden sectors as an absolute value,
while (at least for logical drives in an extended partition) it is 
used relative to the current partition by recent issues of MS-DOS etc.
(usually 3Fh always on current harddisks).
Changing the version number in the OEM label to anything but "3.3" 
will since break OS/2 (and under some conditions - for example unusual 
cluster sizes - also MS-DOS/PC-DOS). However, its not as easy as just 
changing the boot sector setup, because the cause for the 
incompatiblity is not the FORMAT, SYS, or FDISK utility itself, but 
the Generic IOCTL function they use to retrieve that value. Changing 
the reported value there would break all older issues of these 
utilities because they do not contain strict tests for the DOS version 
number as the MS-DOS/PC DOS tools do.
This could cause malfunction when run on future issues of DR-DOS.
So, it's best to just stick with "IBM  3.3" for now...

Matthias

-------------------------------------------------------------------
Matthias Paul, Ubierstrasse 28, D-50321 Bruehl, Germany
eMail: <Matthias DOT Paul AT post DOT rwth-aachen DOT de>
Web  : http://www.rhrz.uni-bonn.de/~uzs180/mpdokeng.html
-------------------------------------------------------------------