MASTER: several methods to save the hard disk

1. The system does not recognize hard disks.
This type of fault is common, that is, the disk cannot be started from the hard disk, and the disk cannot be started from disk a to drive C. The existence of the hard disk cannot be found by using the automatic monitoring function in cmos. Most of these failures occur on the connection cable or ide port, and the failure rate of the hard disk itself is very small. You can re-plug the hard disk cable or change the ide port and cable to perform replacement tests, you can quickly find the fault. If the new hard disk is not recognized, another common cause is the Master/Slave lines on the hard disk. If the hard disk is connected to the ide's master disk, the hard disk must jump to the master disk, hard Disk cannot be detected due to Jumper Error
2. faults caused by cmos
Whether or not cmos is correct directly affects the normal use of the hard disk. Here, it mainly refers to the hard disk type. Fortunately, the current machine supports the "ideautodetect" function to automatically detect the hard disk type. You must use this function to reset the type after connecting to a new hard disk or replacing a new hard disk. Of course, some types of motherboard can automatically identify the hard disk type. When the hard disk type is wrong, sometimes the system cannot be started, sometimes the system can be started, but a read/write error occurs. For example, if the hard disk type in cmos is smaller than the actual hard disk capacity, the sectors behind the hard disk cannot be read or written. If the disk type is multi-partition, individual partitions will be lost. There is another important cause of failure. Because the current ide supports the logical parameter type, the hard disk can adopt normal, lba, large, and so on. If the data is installed in the general mode and the data is changed to another mode in cmos, the read/write error of the hard disk will occur because the ing relationship of the Physical Geology has changed, the original hard disk location cannot be read.
3. startup failure caused by the Main Boot Program
The primary Boot Sector of the hard disk is the most sensitive part of the hard disk. The primary boot program is a part of the hard disk. This program is mainly used to check the correctness of the hard disk partition and determine the active partition, transfers the boot permission to the dos or other operating systems in the active partition. If the program is damaged, it cannot be booted from the hard disk, but the hard disk can be read and written after the software or optical area. The solution to this fault is relatively simple. It is most convenient to use the fdisk of the higher dos version. When the fdisk with parameters/mbr is running, the primary boot program of the hard disk will be directly replaced (overwritten. The Main Boot fan area of the hard drive is built by this program. fdisk.exe contains the complete hard drive Main Boot Program. Although the dos version is constantly updated, the Main Boot Program of the hard disk has not changed, from dos3.x to the dos of ipvs95, so you only need to find a dos boot disk to start the system and run this program to fix it. Other tool software such as kv300 also has this function.
4. startup Fault Caused by Partition Table Error
Partition Table errors are serious hard disk errors. Different errors may cause different losses. If there is no active partition flag, the computer cannot start. However, you can read and write the hard disk after booting the system from a soft or optical area. You can use fdisk to reset the active partition for repair. If a partition type is incorrect, the loss of a partition may occur. The fourth byte of the partition table is the partition type value. Normally, the basic dos partition value larger than 32 MB is 06, and the extended dos partition value is 05. If you change the basic dos partition type to 05, the system cannot be started and the data in the partition cannot be read or written. If you change 06 to dos, for example, efh, dos considers that the partition is not a dos partition and cannot be read or written. Many people use this type of value to encrypt a single partition and restore the original correct type value to restore the partition to normal. There are other data in the partition table used to record the start or end address of the partition. Damage to the data will lead to confusion or loss of the partition and generally cannot be restored manually. The only method is to re-write the data in the backup partition table, you can also obtain partition table data from other hard disks of the same type and with the same partition status. Otherwise, other data will be lost permanently. When performing operations on the primary Boot Sector, you can use tools such as nu to perform operations conveniently. You can directly read, write, or edit the primary Boot Sector of the hard disk. Of course, you can also use debug for operations, but the operations are cumbersome and risky.
5. Hard disk failure caused by incorrect partition valid mark
There is also an important part in the Main Boot Sector of the hard disk, that is, the last two bytes: 55aah, which is the effective symbol of the sector. When the disk is started from a hard disk, floppy disk, or optical area, the two bytes are detected. If the disk exists, the hard disk exists. Otherwise, the hard disk is not recognized. When this flag is enabled, it will be transferred to rombasic or prompted to be put into a floppy disk. You cannot transfer data from a floppy disk to a hard disk when it is started. This can be used to encrypt the entire hard disk. You can use the debug Method for recovery. In addition, the dos boot sector still has such a flag. When the dos boot sector does not have a boot flag, the system starts to display "missingoperatingsystem ". The primary Boot Sector repair method can be used in the repair method, but the addresses are different. The more convenient method is to use the common repair method of the following DOS system.
6. startup Fault Caused by dos boot System
The dos boot system consists of the dos Boot Sector and the dos system file. System files mainly include io. sys, msdos. sys, and command.com. command.com is a dos shell file, which can be replaced by other similar files, but is a required file for dos Startup by default. In windows 95, msdos. sys is a text file that is required to start windows. However, this file is not used when only dos is started. However, when a dos boot error occurs, you can boot the system from a floppy disk or a CD, and then use sysc: transfer the system to repair the fault, including the Boot Sector and system files can be automatically repaired to the normal state.
7. Read/write failures caused by FAT tables
The FAT table records the storage address of the hard disk data. Each file has a set of connected FAT chains to specify the address of the cluster to store. Corruption of the FAT table means the loss of file content. Fortunately, the DOS system provides two FAT tables. If the current FAT table is damaged, the second FAT table can be replaced. However, because the length of the FAT table of disks of different specifications and the address of the second FAT table are not fixed, you must find the correct position in the fix, some tool software such as nu has such repair functions and is very convenient to use. Debug can also be used to achieve this operation, that is, use its m command to move the second FAT table to the first table. If the second FAT table is damaged, the hard disk cannot be restored to its original state, but the file data is still stored in the data area of the hard disk, you can use the chkdsk or scandisk command to fix the issue *. chk file, which is the loss of the sector data of the FAT chain. If it is a text file, it can be extracted from it and the complete file can be merged. If it is a binary data file, it is difficult to restore the complete file.
8. Guide Fault Caused by directory Table Corruption
The directory table records the file name and other data in the hard disk. The most important one is the starting cluster number of the file. Because the directory table does not have the automatic backup function, therefore, if the directory is damaged, a large number of files will be lost. One way to reduce the loss is to use the above chkdsk or scandisk program to search the chk file from the hard disk. If the directory table is damaged, the first cluster number is lost, when FAT is damaged, the chk files are generally complete file data. Each chk file is a complete file, and the original name can be used to restore most files.
9. Data Recovery during accidental deletion of partitions
After the hard disk partition is deleted using fdisk, the data in the hard disk disappears completely. If the hard disk is not formatted, the drive is invalid. If you understand how fdisk works, you will know that fdisk only rewrites the content in the primary Boot Sector of the hard disk (0 sides, 0 sectors, 1 sectors. Specifically, the partition table information of the hard disk is deleted, and the data of any partition in the hard disk is not changed. The preceding Partition Table error repair method can be counterfeited, that is to say, you can recover the original partition, that is, data, only after the partition or re-partition. If you have formatted the partition using format, restore the partition data in the following method after the partition is restored. 10. Recover accidentally formatted Hard Disk Data
In the high dos version, the formatting operation format creates disk information for restoring formatting by default. In fact, the dos Boot Sector of the disk is used, all contents of the FAT partition table and directory table are copied to the last several sectors of the disk (because the following sectors are rarely used), and the content in the data area is not changed at all. In this way, you can run 'unformatc: 'to restore the original file allocation table and directory table, thus restoring the hard disk information. In addition, dos also provides a miror command to record the information of the current disk for formatting or restoration after deletion. This method is also effective.