Atari MEGA STe Technical Information download pdf (Page 11)

As we have seen due to the constraints imposed by the TOS file systems and the DOS file systems it

seems that it is only possible to access Small FAT16A (≤ 32 MB) DOS partitions with an Atari.

However the BigDOS freeware allow access to Large DOS partitions. BigDOS works with several

hard disk driver for example HDDRIVER and CBHD. But unfortunately it does not work with some

other drivers like the ICD AdSCSI or PPDRIVER hard disk driver. See BigDOS section for more

information.

We have seen most of the problems related to the file system (for example the fix value of SPC=2)

come from code inside GEMDOS. As BigDOS replaces GEMDOS at boot time it allows to remove

many of these limitations. More specifically it permits the support of SPC values of up to 64, and the

maximum number of sectors is specified as a 32-bit value (instead of the TOS 16-bit value). Therefore

BigDOS can deal with more than 65536 big logical sectors and this removes the 32MB limitation.

For example using BigDOS and HDDRIVER it is possible to create several 2GB partitions on an 8GB

SD Card and to successfully transfer data from Atari and PC platforms.

2.2.4 Huge DOS/FAT Partitions

By Huge DOS partition we mean partitions with a size ≥ 2GB. These partitions are referred as:

 Type $0B (aka FAT32) with a size range of 512MB – 2TB

 Type $0C (aka Extended FAT32) with a size range of 512MB – 2TB

It is not possible to directly access huge DOS/FAT partitions on Atari (even when using BigDOS) with

the Atari hard disk drivers discussed in this document.

You should know that there are some solutions to access Huge DOS partitions on an Atari (for

example by using Mint) but they are not covered in this document.

2.3 TOS&DOS Partitions

The PPDRIVER and HDDRIVER hard disk drivers described in this document use a hybrid type of

partition called TOS&DOS (or TOS&Windows) partitions. These partitions are processed by Windows

PC computers as DOS/FAT partitions and by Atari computers as TOS partitions. For each TOS&DOS

partition two boot sectors are written: one for the DOS file system and one for the TOS file system.

The maximum size of a TOS&DOS partitions follows the TOS file system limitation (for example

512MB for TOS ≥ 1.04). There is no standard for this type of partition and even though HDDRIVER

and PPDRIVER packages use similar technique the two drivers are in practice incompatible.

TOS&DOS partitions are accessible on both Atari and PC platforms, they can be made bootable on

Atari, and they can have a large size for example up to 512MB for TOS 1.04. Therefore they are well

suited for data transfer between Atari and PC computers using SD cards plugged for example into

CosmosEx device.

 IMPORTANT WARNING: A TOS&DOS partition is not a regular TOS partition and therefore it should

only be accessed on the Atari with the matching hard disk driver. For example using the ICD

AdSCSI hard disk driver gives the impression to access TOS&DOS partitions correctly (it even

report correctly the size) but if you try to read beyond the first 32MB of the partition you will get

incorrect results and even worse if you try to write you will definitively corrupt the partition.

2.4 Notes on Creating and Installing Partitions

2.4.1 Creating TOS Partitions

As we will see later all the Atari Hard Disk driver packages provide a utility that to create TOS

partitions. It is interesting to note that whatever hard disk driver utility you use the resulting TOS

partitions follow the AHDI standard and therefore will be compatibles with all HD drivers. Therefore

you can use the partitioning tool from one package and use the resulting TOS partitioned drive with

any other Atari hard disk driver.

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Atari MEGA STe Technical Information Page 11

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