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There are two types of partitions:
The Primary partition contains several control structures and the actual file and directory data.
The Extended partition is a special kind of partition which is itself subdivided into one or several
primary (aka as secondary) partitions allowing a number of partitions superior to 4 on the disk.
A primary partition contains:
The Boot Sector located at the very beginning of the partition (logical sector 0). It contains an
important area called the BPB (BIOS Parameter Block) that gives basic file system information.
Frequently it also contains the boot loader code.
The FATs are maps of the Data, indicating which clusters are used by files and directories.
The Root Directory stores information about the files and directories.
The Data Region is where the actual file and directory data is stored.
Most of the problems of compatibility between the TOS and FAT file systems are located in the BPB
area of the Boot Sector. Following is a description of the critical parameters of the BPB:
Two important parameters in the BPB are the number of bytes per sector (BPS) and the number of
sectors per cluster (SPC). They are interpreted differently by TOS and DOS/FAT but together they
define the notion of Logical Sector
1
. On a TOS file system a Logical Sector = BPS and can range
from 1024 to 8192
2
Bytes and the SPC is always equal to 2. On a DOS/FAT file system a Logical
Sector = BPS * SPC. The BPS is always 512 bytes but the SPC can range from 2 to 128 resulting
to logical sector of 1024 to 65536 Bytes. Therefore we can see that the two file systems use a
different scheme to define logical sectors bigger than 512 bytes. For example a logical sector of
8192 bytes is achieved with a BPS = 8192 and a SPC = 2 on the TOS file system. The same 8192
bytes logical sector is achieved with a BPS = 512 and a SPC = 16 on the DOS file system.
Another important parameter in the BPB is the total number of sectors. On a TOS file system this
number is stored as a 16-bit quantity (NSECTS parameter). This results in a maximum size of
512MB (2^16 * 8192 bytes) for a TOS partition
3
. On DOS/FAT file system the number of sectors
can be stored as a 32-bit quantity (HSECTS parameter) allowing definition of partitions up to 2TB.
For technical details look at TOS Boot sector and DOS/FAT Boot sector
1.3 Preparing a Drive
A drive needs to be “prepared” before it can be used to store data. With modern drive, this is done in
two steps:
The first step is called partitioning:
Hard drives are divided into smaller logical drive units called partitions. In this way a single
hard drive can appear to be two or more drives to the OS. Besides simply keeping drive sizes
under the file system size limits, dividing a drive also allows partitions to be used for specific
purposes, keeping the drive organized.
The second step is called high-level formatting (also referred as formatting or initialization
4
):
This is the process of creating and initializing the basic disk's control structures: namely the
Boot Sector, the FATs, and the Root Directory as described in the previous section.
Note: On old hard disks you also had to
format
them (also referred as
low level formatting
)
before partitioning. Low level formatting allows the magnetic medium on the surfaces to be divided
into tracks containing numbered sectors that the controller can find. With “modern” SCSI / IDE
drives and with drives using SD cards this operation is not required anymore and therefore is not
described in this document.
1
Note that the term logical sector is used differently on Atari and PC platforms.
2
32768 for TOS4.0 on Falcon (but officially supported only 16384)
3
For TOS < 1.04 max partition size = 256MB (2
15
* 8192), and for TOS 4.x max partition size = 2GB (2
16
* 32768).
4
The term “Formatting” is used in PC environment while the term “Initialization” is often used in Atari environment.
- ATARI HARD DISK 1
- FILE SYSTEMS 1
- REFERENCE GUIDE 1
- Table of Content 2
- How to Read this Document 5
- PART I – ATARI HARD DISK 7
- FILE SYSTEM 7
- PARTITIONING GUIDE 7
- 1.1 Hardware Consideration 8
- 1.3 Preparing a Drive 9
- 2.1 TOS Partitions 10
- 2.2 DOS/FAT Partitions 10
- 2.3 TOS&DOS Partitions 11
- 3.2 TOS Maximum Path Depth 14
- *** OUT OF INTERNAL MEMORY: 16
- *** SYSTEM HALTED *** 16
- 4.2.1 Disk Change Support 18
- 4.3.1 Satan device 18
- 4.3.2 UltraSatan device 18
- 4.4.1 Partitioning a drive 19
- 4.4.1.4 Actual Partitioning 20
- Auto boot 20
- 4.5.1 Partitioning a drive 22
- 4.5.6 Driver usage 23
- 4.6.1 Partitioning a drive 24
- ) and not in megabytes (1024 25
- 4.7.1 Partitioning a drive 28
- 4.7.2 Enabling Auto boot 28
- Chapter 5. PC Utilities 31
- 5.4 Partition Table Editor 34
- 5.5 PC File Transfer Tools 34
- Chapter 6. Atari Utilities 35
- 6.2 FOLDRXXX Utility 36
- 6.3 TOS14FIX Utility 36
- 6.4 POOLFIX3 Utility 36
- 6.5 CACHEXXX Utility 36
- 6.6 STE_FIX Utility 36
- NOT TRY TO USE the partition 37
- PART II – ATARI HARD DISK 38
- TECHNICAL INFORMATION 38
- 8.1 Hard Disk Primer 39
- 8.3 TOS Partition Size 41
- 9.1 TOS Hard Disk Layout 42
- 9.2 TOS Root Sector 42
- 9.3 TOS Standard Partition 43
- 9.4 TOS Extended Partition 44
- 9.5.1 TOS Boot sector 46
- 9.5.3 TOS Root Directory 47
- 9.6 TOS Boot Sequence 50
- 10.6.1 DOS/FAT Boot sector 55
- Length 56
- 11.2 TOS&DOS MBR / EMBR 64
- 11.3.1.1 HDDRIVER 67
- 11.3.1.2 PPDRIVER 67
- References 69
- History 69
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