Superfloppy Utility for OS/2

Preface

I made this tool to share data on 640MB magneto-opticals with different operating systems. It should work for media with 1024 bytes per sector too. It runs with OS/2 and Windows NT.

Background

The OS/2 driver model for (optical) devices with >512 bytes per sector:

1. The 'official' way
   IBM tells you to use OPTICAL.DMD. Well, this driver is very old. It only supports FAT Superfloppies and uses at least no write caching.
2. With Fujitsu devices
   If you have a Fujitsu MO-drive there is a OS/2 driver available from their homepage. It supports all FAT based formats I know, but it also uses no caching. And unfortunately it has a bug (like the DOS driver too). This bug ist not very common but it will destroy the integrity of the FAT file system - so your data is unsafe.
3. The N512DASD driver - It's the only way for HPFS formatted media
   The removable media support of IBM's NEWDASD package (and newer fixpacks) only includes 512 bytes per sector media. If you have optical devices greater than 230 MB you will usually have 1024 or 2048 bytes per sector. The filter driver N512DASD.FLT will logically convert them into devices with two or four times as many sectors of 512 bytes.
   This works fine but the resulting formats are incompatible with other operating systems. For this application this utility can help.

Installation

Copy the file mo640.exe anywhere in your PATH.

Youe need the following drivers installed in your CONFIG.SYS:

BASEDEV=N512DASD.FLT
BASEDEV=OS2DASD.DMD /OF

Usage

• Format a 640MB MO disk as FAT/VFAT superfloppy (preferably not with OS/2) or take an existing superfloppy.
• Insert it into your MO drive (OS/2). You will see an empty directory instead of an error message - I suppose that OS/2 ignores the bytes-per- sector field in the boot record completely. DO NOT WRITE ANYTHING TO THE DISK NOW.
• Enter now MO640 number: at the OS/2 command prompt where number is the drive number of you MO drive. Usually this is the number of your harddrives plus one. You can use FDISK to find it out.
  Example: mo640 3:
  The media will be converted to an OS/2 (i.e. N512DASD) compatible format.
• Eject the media.
• Insert it again. You should now be able to access it without any restrictions. (including the VFAT IFS)
• The media is no longer compatible with other operating systems with one exception: The Fujitsu MO-driver for DOS and OS/2 still can access it. I guess that they used nearly the same trick than I did.
• If you want to use this media with other OSs than you have to convert it back to its original state. Enter MO640 number: /ssector size at the OS/2 command prompt. sector size should be the physical sector size of the particular media. It cannot be determined automatically because of the N512DASD driver.
  Example: mo640 3: /s2048
  The media is now accessable by other operating systems and of course not by OS/2 after you removed it.

The behavior of 512 bytes per sector media is unchanged. You can share superfloppies and partitioned media with other operating systems. You do not need this utility in this case.

My recommendation: Use FAT superfloppy for data exchange and HPFS partitioned for OS/2 only.

WinNT

Normally you do not need any utility to access opticals with WinNT. However, there is one good reason for a WinNT port of this tool: if you forgot to convert a disk back before using it with Win.

The WinNT version is called mo640nt.exe and is included within this package.

Please notice that the command line syntax is slightly different:

mo640nt drive:
In this case drive is a drive letter. By default the disc is converted to 2048 bytes per sector. If you have media with 1024 bytes per setctor, you need the /s1024 switch.

It is not necessary to eject the media after conversion. You can use it immediately.
I have to say: the hole DASD implementation of NT is much cleaner and easyer to use.

• Do not use this utility with anything else than MO discs. Normally this should result in an error message, but it may not for other Superfloppy removables (e.g. ZIP).
• The WinNT version will definitely not work on DOS based operating systems like Win9x.

Restrictions

• This utility works only for SUPERFLOPPY formatted devices and cannot be easyly modified to work with other formats like partitioned media.
• The converted media is only readable by OS/2 and the (buggy) Fujitsu driver - DOS and OS/2 version only.
• I found some low level disk utility which cannot access the converted media under OS/2. I looks like they do not handle the special reserved sector entry in the bootblock correctly.

Download

ToDo

Of course, it ist not very comfortable to convert the media always. And maybe, you forgot to convert it back before using it with Win...

• It would be much easyer to handle media whitch is virtually converted by a filter device driver - but much more comlicated to program too. I have completely no idea how to program a filter driver. The N512DASD sources would be helpful, but unfortunately it is not open source.
  At this stage it would also be possible to handle partitioned media and - maybe - other file systems like FAT32.
• It might be useful to have a Win9x port of this utility. Feel free to do this job. I will definitely not, because I always keep on running if 95 is coming too close.
• Currently there is no way to format a superfloppy device under OS/2 with this driver configuration. Well, I usually used a disk editor with copy & paste.
  That's a job for another tool.
  Fortunately most of the new disks are formatted as superfloppy.

What does it exactly?

The N512DASD driver changes the number of sectors on the media, so all references within the file system become invalid. Fortunately FAT uses mainly cluster based references. So the only job is to modify the bootblock this way that the clusters have more sectors of smaller size (512) resulting in the same cluster size. Only a few changes are necessary.

Example for 640 MB superfloppy:

offset	before	after	description
0B	0008	0002	bytes per sector (2048->512)
0D	08	20	sectors per cluster (8->32)
0E	0100	0400	reserved sector at the beginning (bootblock) (1->4)
16	2600	9800	sectors per FAT (38->152)
20	4EBC0400	38F11200	total number of sectors (310350->1241400)

The implementation is a little bit more sophisticated. In addition to the example 'short number of sectors' and 'hidden sectors' are processed. Usually they are zero.

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