<fat file System >-DBR

FAT16 is a relatively simple file system, compared to nfts and other file systems, the system learning is easier, easy to get started, but also for the mechanism of data storage and data recovery has certain help. The FAT file system has some drawbacks and cannot support too large data storage.

The FAT16 file system consists of five parts: DBR,FAT1,FAT2,FDT and data.

For the FAT16 file system, the most important is the DBR partition. DBR starts at the FAT16 file system's first sector.

Imagine the computer booting, limited by the BIOS read the master boot of the MBR content to determine the logical drive to start the boycott, and then into the active partition of DBR, by the DBR to boot the operating system. Without DBR, data reads from the FAT16 file system will not be discussed. How important it is to be like DBR! Therefore, for in-depth study of file systems, the composition of DBR internals is necessary. The following small series to lead you into the world of DBR.

Let's take a look at the first picture:

All is 16 binary, looks like the heavenly book ha!

It doesn't matter, I slowly come to the road.

DBR = JMP + OEM + BPB + Bootstrap + Finish

It seems not difficult to look, we continue to chit chat when haha.

1> JMP

Jump instructions, learn the assembly instructions are easy to understand, (plain English: is the two-byte assembly instruction, JMP 3C) then 3C after the 90 is what? I feel good fun ah, untie the truth, Nop Ah, is an empty command. In-depth analysis shows that next executes the instruction is 3E AH. Oh, that's what happened.

2> OEM

It's important to give the device a name. See the Red Line Circle to the section, according to ANSI-ASCII standard translation, the result is MSDOS5.0. Wow, that's exactly eight characters. But what does that mean?

This is a number given by Microsoft Corporation. MSDOS5.0 explains that this FAT16 partition was created by the Microsoft company Windows2000 above the operating system format. I let you look at my plate, don't have fun ha.

See, is the author of the mobile hard disk identification, if can be named Zhuhai.02.uf that how good, I can know is mobile or fixed, ah seems FAT16 still have flaws, I also feel sorry.

Small series very sad, small make up again sad also want to continue to finish. Lets Go on!

3> BPB

BPB, how does the writer feel a bit of bios shadow? Yes BPB is the abbreviation for BIOS parameter block. It's a big play.

0002 means 512Byte per sector;

80 indicates 128 sectors per cluster;

DBR retains 6 sectors;

22 fat; (more to say, to backup ah, to prevent the loss of Ah, one will be enough?) ）

......

Alas, this one says, it is not a good way. 4641543136202020 This must say Ah, this is our file system code AH FAT16, small series here is to say is to hope that the reader to take a serious look at the starting address, you will have a big discovery, find this address, you know the file system type, haha the author a little thirsty, the rest of the said, Interested readers can check their own ha. Oh, go on, be sure to finish.

4> Bootstrap

We used to look at two pictures, carefully observe ha.

The first, is simply a curse, can not understand, the right is simply the birds, pain, helpless. This does not need to understand, I would like to summarize: This code is responsible for the completion of the system file loading, for the partition without installing the system is useless. Look at the annoying, all clear zero, the slightest impact, hard drive open no problem.

5> Finish

It's over, haha. The DBR is about to end. Give a sign 55AA. This is a fixed yo. To say a word, MBR end is also 55AA. It's so funny. DBR analysis is over, good coincidence, just a sector 521Byte. So we sometimes call the DBR a boot sector.

I want to think about it, if I put a part of the DBR inside out, see how you peek at my discarded disk data, hum!

So tired. In this, there is no detailed introduction fat table, about fat table, that is a very interesting thing, the following will introduce the HA.

Instruct

<fat file System >-DBR