Atari MEGA STe Technical Information download pdf (Page 44)

 TOS ≥ 1.04 and ≤ 4.x

 Maximum size of a cluster in number of bytes = 2^14 = 16384

 Size of a cluster in number of logical sectors = 2

 Maximum size of a logical sector in number of bytes = 16384 / 2 = 8192

 Maximum number of logical sectors = 2^16 = 65536

 Maximum size of a partition in number of bytes = 65536 * 8192 = 512 MB

 TOS 4.x (Falcon)

 Maximum size of a cluster in number of bytes = 2^16 = 65536

 Size of a cluster in number of logical sectors = 2

 Maximum size of a logical sector in number of bytes = 65536/ 2 = 32768

 Maximum number of logical sectors = 2^16 = 65536

 Maximum size of a partition in number of bytes = 65536 * 32768= 2GB

9.3.3 Example of layout with TOS standard partitions

In the following example we have a hard disk with 3 standard partitions. The Root Sector contains 3

pointers to the 3 partitions. These partitions can be either regular or big partitions.

9.4 TOS Extended Partition

Extended partition enables a hard disk to contain more than 4 partitions. Only one entry in the Atari

partition table can contain an extended partition. The extended partition is identified by the ASCII

characters “XGM” in the id field of the partition entry. Since an extended partition is not bootable, it

must be preceded by at least one standard partition, so the hard disk can be made bootable. This

requirement makes it impossible for the first partition to be an extended partition.

An extended partition is subdivided into smaller ones. Each subdivision consists of an Extended Root

Sector (ERS), and a Standard Partition. Conceptually, each subdivision is like a stand-alone hard disk

with only one partition on it. These subdivisions are linked together by a pointer in the Extended Root

Sector.

9.4.1 TOS Extended Root Sector

The layout of an Extended Root Sector resembles that of the Root Sector, except that it only

contains the partition table. Only two of the four partition table entries can be used, but not necessarily

the first two. One of them is used to describe the Standard Partition in the current subdivision; the

other one provides eventually a link to the next subdivision. The link should occupy the entry that

follows the entry for the description of the standard partition. The other two unused entries should be

filled with zeroes.

Officially only 1GB is supported by TOS 4.x. However I think that this limitation is related to host adapter support of AHDI

command set (2^11 * 512 = 1GB). With host adapter supporting the ICD extended command set the limit of 2GB should work

fine.

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Atari MEGA STe Technical Information Page 44