USB File System

Meaning

Available

Retention

Bad

Finally, a cluster file

Under a cluster file

DOS boot record formula:

z file allocation table º number of reserved sectors

z root directory º number of reserved sectors + FAT sectors per FAT × number of

z data area º root of the logical sector number + (32 × number of directory entries in the root directory) / number of bytes per sector

z absolute sector number º logical sector number + hidden sectors

z Sector Number º (absolute sector number% number of sectors per track) +1

z head number º (absolute sector number / number of sectors per track)% of heads

z track number º (absolute sector number / number of sectors per track) / heads

Highlights:

1) DBR located at cylinder 0, head 1, sector 1, the logical sector number 0

2) DBR contains a DOS boot program and BPB.

3) BPB is important, thereby calculating the logical addresses and physical addresses.

File allocation table (FAT)

Absolute sector number is: FAT_LBA = DBR_LBA + BPB_wReservedSec is that the file allocation table is a DOS file group

The main part of the weave structure. We know that DOS is the basic unit of allocation of clusters. File Allocation Table is a reflection of the hard disk

The use of all the clusters, the file allocation table by checking that the use of any cluster. Points to a file in DOS

The total space of the first scan with FAT, find the first available cluster, the space allocated to the file, and the cluster in to fill the head

Recorded in the corresponding segment. That formed a "cluster number chain." FAT is the cluster number of a log file table. The first two fields in order to protect the FAT

Left field of 3 bytes is FAT12, FAT16 is 4 bytes. In which the first byte is used to describe the medium

The remaining bytes FFH. BPB same media format.

FAT structure of meaning: The first general FAT table is FF8H or FFF8H.

FAT12

000H

FF0H－FF6H

FF7H

FF8H－FFFH

×××H

FAT16

0000H

FFF0H－FFF6H

FFF7H

FFF8H－FFFFH

××××H

For FAT16, cluster number × 2 for offset address, remove the word FAT is the domain from the FAT.

= Logical sector number data area start logical sector number + (number of clusters -2) × number of sectors per cluster

Cluster number = (logical sector numbers - the data area starting logical sector number) / number of sectors per cluster +2

Highlights:

1) the use of all cluster FAT reflect on the hard drive, it records the file specific location (cluster) on the hard disk.

2 The first cluster number) file (in the table of contents) and the FAT file documented cluster number to string together "cluster number chain"

Repair the damaged file is based on this chain.

3) can be counted by the cluster number of the logical sector number, and vice versa, by a logical sector number can be calculated from the cluster numbers, the formula above.

4) FAT located DBR after its DOS sector numbers starting with 1.

File directory table (FDT)

Absolute sector number is: FDT_LBA = FAT_LBA + BPB_bNumFATs * BPB_wSecPerFAT is that the file directory table,

Another important part of the DOS file organization structure. File directory is divided into two categories: the root directory, subdirectory. Root directory

One can have multiple subdirectories. You can also have a subdirectory under the subdirectory, which form a "tree" file directory structure.

Subdirectory is actually a special kind of file, DOS allocate 32 bytes of directory entries.

Directory entry is defined as follows:

typedef struct {

char FileName [8]; / / ofs:. 0 filename

char ExtName [3];

uchar attribute;

/ / Ofs:. 8 extension

/ / Ofs:. 11 file attributes. Typical values: Archive (0x20), label (0x08).

char reserved [10]; / / ofs: 21 Reserved.

uint time;

uint data;

uint StartClus;

ulong FileLength;

}DIR_tag；

/ / Ofs:. 22 hours

/ / Ofs:. 24 date

/ / Ofs:. 26 start cluster number

/ / Ofs:. 28 file length

Filename directory entry in the first byte of the area also has a special significance:

00H representatives unused.

05H represents the actual name E5H.

E5H representative of this file has been deleted.

The significance of this byte directory entry attribute area of each bit is as follows:

7 6 5 4 3 2 1 0

No repair repair sub- volume series implicit only

With change change target standard system of Tibetan Reading

Standard Standard recorded

Chi Chi

Genus genus genus

Sex sex sex

WINDOWS use long file names on the table said "reserved" this area.

Time: time = Hr * 2048 + Min * 32 + Sec + 2.

Date: time = (Yr-1980) * 512 + Mon * 32 + Day.

Relationship between the cluster number and the logical sector number is:

Logical sector number = (cluster number - 2) × number of sectors per cluster + data area starting logical sector number.

Highlights:

File directory is to record all the files subdirectory name, extension attributes, create, or delete the last modified date. Culture

Pieces start cluster number and a registration form file length.

DOS DIR content listed in the table is obtained according to the file directory.

Fill in the file start cluster number of the file directory, and the remaining clusters are filled in on the FAT cluster position.

The data area (DATA)

z Data Area absolute sector number º root of the absolute sector number + (32 × number of directory entries in the root directory) / number of bytes per sector

Expression: DATA_LBA = FDT_LBA + (32 * BPB_wRootEntry) / BPB_wBytesPerSec.