Four, FAT partition principle.

First to a structure:     We now focuses on the FAT partition data format of how the store. MICROSOFT first FAT partition format is supported partition format, according to the median FAT table for each share of cluster chain (related concepts will be mentioned later) into fat12, fat16, fat32 three formats "variant", but its basic storage is similar.     Careful study of the composition of the structure in Figure 7 fat16 and fat32 partition. Explained in order below DBR, FAT1, FAT2, root directory, the data area, the concept of the remaining sectors. Address if no special tips mentioned are the internal partition offset.
    


 

4.1 About DBR.

    DBR region (DOS BOOT RECORD) means that the operating system boot record area usually occupied by the partition sector 0 of 512 bytes (also occupied by other special circumstances reserved sectors, we start with the first 0). In this 512 bytes in fact turn, jump instructions, the manufacturer logo and operating system version number, BPB (BIOS Parameter Block), extended BPB, os boot program, marks the end of several parts. In the most used FAT32 partition DBR an example of each byte meaning. Figure 8. Figure 8 corresponds to the interpretation of Table 3   
    

 
 

Figure 9 shows the winhex on Figure 8 DBR related parameters explained:     According to the legend on top, we discuss the significance DBR parameters for each byte.           MBR transfers CPU execution to the boot sector, so the first three bytes of the boot sector must be legitimate executable x86-based CPU instructions. This is usually a jump instruction, which is responsible for the next couple of bytes skipped unenforceable (BPB and extended BPB), jump to the operating system boot code section.     After the jump instruction is an 8-byte OEM ID, which is a string, OEM ID identifies the format the partition operating system name and version number. In order to retain compatibility with MS-DOS, and Windows 2000 is usually the disk is formatted in FAT16 and FAT32 disks recorded in the field "MSDOS 5.0", on an NTFS disk (on ntfs, another state), Windows 2000 record is "NTFS". Typically OEM ID field appears "MSWIN4.0" was 95 at the formatted disk Windows, OEM ID field appears "MSWIN4.1" on is Windows 95 OSR2 and Windows 98 formatted disk.     Offset from the beginning of the next is a description 0x0B enables the executable boot code to find information relevant parameters. Usually called BPB (BIOS Parameter Block), BPB generally start at the same amount of displacement, and therefore, are in a standard parameters known location. Disk capacity and geometry variables are being sealed in BPB. Since the guide is a sector portion of the first jump instruction x86. Therefore, in the future by the end of the additional new information BPB, BPB can be extended. The jump instruction needs only to make a small adjustment can adapt to changes in BPB's. Figure 9 has a list of the names and values ​​of the project, in order to study the system, for Figure 8, the BPB meaning FAT32 partition format and extended BPB interpretation of the meaning of the form, as shown in Table 4 and Table 5.