Atari MEGA STe Technical Information download pdf (Page 67)

11.3 TOS&DOS Partition Structure

11.3.1 TOS&DOS Boot Sector

DOS&TOS partitions contain two Boot Sectors: one for DOS and one for TOS.

11.3.1.1 HDDRIVER

As we have seen in previous section HDDRIVER have the first partition entry in the MRB pointing to a

DOS Boot Sector at location 0x07E00. This boot sector follows the DOS standard and you can go to

DOS/FAT Boot sector section for more information.

Example of DOS boot sector created by HDDRIVER:

Offset 0 1 2 3 4 5 6 7 8 9 A B C D E F

00007E00 EB 3C 90 4D 53 44 4F 53 35 2E 30 00 02 20 11 00 ë< MSDOS5.0

00007E10 02 00 02 00 00 F8 80 00 3F 00 3C 00 3F 00 00 00 ø€ ? < ?

00007E20 38 A6 0E 00 80 00 29 CC 56 37 61 4E 4F 20 4E 41 8¦ € )ÌV7aNO NA

00007E30 4D 45 20 20 20 20 46 41 54 31 36 20 20 20 00 00 ME FAT16

Few things to note:

 As we can see the BPS at location 0x7E0B is 512 (0x0200) and the SPC is 32 (0x08). This

gives a logical cluster size of 16384 (512 * 32)

 The reserved sector count at location 0x800E is 17 (0x0011). Therefore the position of the first

FAT is at logical sector 17 (relative to the DOS partition).

 As this is a large DOS partition, the number of sectors is 960056 specified at 0x07E20. This

gives a partition size of 491548672 (960056 * 512)

The third partition entry in the MBR is pointing to the TOS boot sector at location 0x08000. This boot

sector follows the TOS standard and you can go to TOS Boot sector section for more information.

Example of TOS boot sector created by HDDRIVER:

Offset 0 1 2 3 4 5 6 7 8 9 A B C D E F

00008000 60 32 90 4D 53 44 4F 53 35 2E 30 00 20 02 01 00 `2 MSDOS5.0

00008010 02 00 02 63 EA F8 08 00 3F 00 3C 00 40 00 00 00 cêø ? < @

00008020 00 00 00 00 80 00 29 CB 56 37 61 4E 4F 20 4E 41 € )ËV7aNO NA

00008030 4D 45 20 20 48 78 FF FF 3F 3C 00 48 4E 41 5C 8F ME Hxÿÿ?< HNA\

Few things to note:

 As we can see the BPS at location 0x800B is 8192 (0x0800) and the SPC is 2. This gives a

logical cluster size of 16384 (8192 * 2)

 The reserved sector count at location 0x800E is 0x0001. Therefore the position of the first FAT

is at logical sector 1 * 8192/512 = 16 (relative to the TOS partition).

 The number of logical sectors is 60003 (0xEA63) specified at location 0x8013. This gives a

partition size of 491544576 (60003 * 8192).

As we can see both Boot Sector points to the same FAT, Root Directory, and data segment.

11.3.1.2 PPDRIVER

PPDRIVER uses a standard first partition entry in the MRB pointing to a DOS Boot Sector at location

0x07E00. This boot sector follows the DOS standard and you can go to DOS/FAT Boot sector section

for more information.

Example of DOS boot sector created by HDDRIVER:

Offset 0 1 2 3 4 5 6 7 8 9 A B C D E F

00007E00 EB 3C 90 50 50 47 44 4F 44 42 43 00 02 08 05 00 ë<.PPGDODBC.....

00007E10 02 00 02 00 00 F8 84 00 00 00 00 00 00 00 00 00 .....ø„.........

00007E20 BC FB 03 00 00 00 00 00 00 00 00 00 00 00 00 00 ¼û..............

Few things to note:

 As we can see the BPS at location 0x7E0B is 512 (0x0200) and the SPC is 8. This gives a

logical cluster size of 4096 (512 * 8)

 The reserved sector count at location 0x7E0E is 0x0005. Therefore the position of the first FAT

is at logical sector 5 (relative to the DOS partition).

 As this is a large DOS partition, the number of sectors is 261052 (0x00 03 FB BC) specified at

location 0x08020. This gives a partition size of 133658624 bytes. For a small partition this field

would have been set to 0 and the size would have been specified at location 0x8013.

 PPTOS does not fill the FAT16 extended BPS (location 0x08024-0x0802D)

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Atari MEGA STe Technical Information Page 67

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