Previous MESS HD conversion procedure

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The following description was contributed by Tim Tesch on the TI mailing list on April 11, 2007. It applies for MESS version 0.86 and up to version 0.134.


  • I included two different attempts, because I was experimenting with MYS (the SCSI formatter) and repairing a critical error in its calculation of total Allocation Units (AUs) on a full platter.
  • My platter was formatted at >FFFF Allocation Units, which exceeds the limitations of the HFDC bitmap. This was an error in MYS, unnoticed since SCSI does not use Cylinder/Head/Sector parameters to calculate the location of a sector on the disk.

However, MFM does use these parameters, as does MESS, which is how I discovered the problem.

  • Because MYS formatted the platter in this manner, it was necessary to fix certain pointers manually.
  • xxx.hd images are uncompressed, special formats that allow read/write access to the data from MESS. This is an important note ;)
  • Uncompressed images can produce the RAW data, allowing one to create a platter from a MESS image.

MESS platter to .HD process

1. Create blank drive using corresponding Cylinder/Head/Sectores/sectorsize parameters:

try 1:chdman -createblankhd 128mbver3.hd 1024 16 32 256
try 2: chdman -createblankhd 128mbver3-2.hd 1024 16 32 256

2. Copy RAW data into a compressed file. the file "110404b" is the sector dump of my SCSI platter.

try 1: chdman -createhd 110404b 110404b-output.hd 1024 16 32 256
try 2: chdman -createhd 110404b 110404b-output2.hd 0 1024 16 32 256

[MZ] Note: the second line is missing "0". This is an incorrect line.

3. copy the "RAW" CHD image into the uncompressed HD image.

Try 1: chdman -copydata 110404b-output.hd 128mbver3.hd
Try 2: chdman -copydata 110404b-output2.hd 128mbver3-2.hd

NOTE: >FFFF 20 444950 = max sec, DIR

Now... you can edit the RAW image data but NOT the ".HD" file. This means you can make some corrections ahead of time. But once you COPY the raw data into the uncompressed HD image, you cannot edit the file. Why? - CRC/ECC values are computed and used by MESS. Editing the sectors in the .HD file will result in errors and may stop MESS from mounting the image.

4. Using SECTOR ONE or DUHARD80, change total AUs from >FFFF to >F800. Only needed if your image was formatted incorrectly.

5. Edit Sector 0 disk parms. Reflect proper sec/AU and heads. This will be different depending on your image size. For my 128MB image, the parameters were as follows:

>7F =
| |--- heads-1 (16-1 = 15 = >F)
|------(sectors per AU) -1 = 8-1 = 7

6. Edit MAX AU byte in the Directory Descriptor Records - referenced by sector 0. It appears the HFDC only reviews the MAX AU word in the root and one level deep. Therefore, the pointers in the ROOT and first level folders MUST be corrected. >F800 is the maximum value.

7. test again. TREE? read a file?