Atari ST - PC: compability of hard disks and partitions

  As most of users know, Atari ST and followers (Falcon, TT) use FAT16 filesystem by hard disks. Same F.S. use DOS, Windows on PCs. So, can we just simple attach hard drive from Atari on PC, and accessing files, partitions on it?
  Unfortunately not. First problem is different partition table. Atari uses AHDI partition table, what is similar to those by PCs, but is not compatible.
  This is smaller problem, and is very easy to override: hard disk driver on Atari just needs to recognise PC partition table, and mount FAT16 partitions from disk. Most popular hard disk driver programs for Atari can do it.
  Second problem is bigger: different FAT16 partition parameters. It is much harder because FAT16 support is inside ROM TOS - DOS, Windows. And is much complexer than partition mounting. In praxis, only small partitions up to 32MB are compatible. Bigger ones will not work on other system. Reason is different logical sector size and different count of sectors in one cluster by 2 systems.

  There is fine freeware program BigDOS, which adds support for DOS-type FAT16 partitions for Atari machines. With it DOS FAT16 partitions up to 2GB are accessible on ST. Program has some flaws - it disables partitions under 32MB, works not well with all partition parameters. And must be started from AUTO folder (due it's nature - before GemDOS init).
  In praxis it looks so: attach PC hard disk on Atari,  run BigDOS from AUTO folder, and
install driver (from floppy). Then FAT16 partitions are fine accessible in most of cases. Not too elegant, but on PC side nothing extra is required. It is possible to solve it with autoboot from hard disks - then BigDOS (with it's AUTO folder)  must be placed in first 32MB of boot partition (TOS 1.04 and above), or must be on partition smaller than 32MB (see above why is it not good).
  Other way is Mint: it has own filesystem driver, and will work with DOS FAT16 partitions. And with FAT32 partitions (not too large ones, but 11GB worked for me).

  Today is high demand for easy data transfer on relation Atari-PC.
 For AHDI partitioned drives on PC side we have Gemulator Explorer, which allows file copy with Atari hard disks. But only few variations, plus it is outdated and works not good in Win XP.
 I made Drive Image, which does file transfer, plus making, writing image files of drives, cards, partitions. It is good for AHDI partitioned drives and  partitions up to 512MB at moment. Recognises swapped L/H by IDE attached drives, may extract partitions etc.

Next step is special partitioning , with which Atari can access directly DOS partitions up to 512MB, without BigDOS. With special driver, very similar with those on site. It will be not free, mostly because of partitioning program and lot of time and money spent in development and testing with diverse hard disks, cards, adapters. Price will be about 10 Euros. Autoboot is possible from drives, cards partitioned with, and no limit for first partition size. Up to 2048GB capacity...

  Pro & contra for AHDI and DOS partition systems:

   And there is another big reason for using DOS partitioned drives: by new, large capacity hard disks it is big problem how to use all space on Ataris. Partition sizes and count is limited, so above 10GB we are forced to use FAT32 partitions. But they are not accessible without Mint, which is simple not for ordinary ST(E) machines, especially not for those with 1-2 MB RAM. With DOS compatible partitioning we may set some FAT32 partitions for data storage, backup of PC, or even some rare used Atari stuff.

Multiple partitions on memory cards under Win XP

  P. Putnik  Dec. 2007.