Some prior knowledge for hard drive data recovery

 Data recovery is a kind of grand learning. When it comes to data recovery, people then think of hard disk data recovery. Even if we do not need to recover data, we also need to know knowledge. They are benefit for us in our daily practical operation and application.

Data structure of hard disk

1.      Master boot sector

The master boot sector is located in sector 1, cylinder 0, track 0 of the drive. It include the master boot record and partition table. The master boot record is to check the partition table and make sure that which partition is master boot sector. And bring the initiator to memory to perform when the program ends.

2.      OS Boot Record

OBR(OS Boot Record) is the operating system of master boot sector. It is usually located in sector 1, cylinder 1, track 0 of the drive, and is the first sector which the operating system can visit. It includes a bootstrap and a parameter record table of this partition which called BPB (BIOSParameterBlock). BPB pieces record some parameters like the start sector, end sector, file formats, descriptors of drive medium, root directory size, FAT number, allocation units pieces, etc.

3.      File allocation table

FAT is the file allocation table. It is the file addressing system of DOX and Win 9x. Considering the safety, there are two FAT . The second is the backup of the first FAT. FAT is comes after OBR ,and its size is determined by the size of this partition and file allocation unit.

4.      Data areas

Although data have account for most of the space, they do not make any sense without the above parts, for they just are some  boring binary codes .If you defragment your drive disk regularly, the data areas may be sequential. In that case, even if all the MBR/FAT/DIR are damaged,  you still can use the disk editing tool. Once the beginning and ending location of a file are found, this file is possible to be restored.

The principle of data storage

1.      Read of file

The operating system read file information from directory area and read corresponding data from cluster. And then it find the 0023 unit in FAT. If this unit has a signal of file end, then the file end. If not, read another cluster until it meet the end signal.

2.      Write of file

When to save a file, the operating system find a gap first in dir zone to write the corresponding information like file name, size , creation time. And then find a free space to save file in data area and write the first cluster in data area to dir area.

System startup process

1. The system performs POST(power on self test) to check its own hardware.

2.  Read the partition record and boot record. When the microcomputer has checked the hardware, it shows the hardware is in good condition and corresponded with CMOS. Then it will boot from the corresponding device according to CMOS to read the partition record and main boot record of disk.

3. Read DOS boot record. After the correct reading and inspecting of partition record and main boot record, it performs main boot record  and make a further read for DOS boot record , and then perform this DOS boot record.

4. Load system hidden file. Save the hidden file IO.SYS in DOS system to memory and load the FAT file system and disk condensing program.

5. Achieve DOS pattern configuration. After load the hidden file, the microcomputer will perform them and the system configuration files. And load the drivers defined in Config.sys.

6. Call into command interpreters. The system loads command mange system to achieve cooperative management to all kinds of system operation command.

7. Executing the batch file. The microcomputer will execute all the commands in batch file.

8. Load Win.com. That is to all the drivers and start-up executable in Windows for execution. Then the start-up has finished.

If you still have trouble in data recovery, you can ask the Hdata technical support team for help.