The most useless degrees….
SALVING OF FLOATING DRY DOCK AFDM-2 1965 U.S. NAVY DOCUMENTARY FILM 79014
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Let us describe the process of manual data recovery if files are deleted or files from damaged partitions when working in. The problem is that there is no corresponding software in this operating system. Unfortunately, third-party data recovery programs do not always use all recovery options. The lack of complete documentation on the low-level structure of the control block made the situation worse. What if one day you find that your computer no longer starts or some logical partitions are suddenly unavailable? First, you need to figure out the cause of the failure: physical disk damage, controller failure, or file system damage.
Hard disks have a limited service life, usually several years. Sometimes, the characteristic click sound during initialization can be used to identify the malfunction of the device. The disc can disappear with a few clicks without rotating. During initialization, you will be notified of this problem. In this case, the hard disk should be repaired. If the cost of the lost information greatly exceeds the cost of the disk itself, you should contact an expert, but it is not cheap. If the electronic device located outside the sealed space of the disc fails, replace or repair the corresponding board. To do this, you usually have to remove another disc of the exact same type. If the parts inside the cartridge are damaged, there will be more problems. First, you need to disassemble a damaged disk on a so-called disk that can ensure that there is no dust. Then, the circuit board should be replaced by removing the electronic device from another disk. The repaired disk will be closed, and then only the operation of copying information by sector to the third disk will remain. Therefore, if a hard drive containing valuable information fails, be prepared to sacrifice another hard drive for repairs and find a third hard drive to copy the recovered data. If you suspect that the disk controller is damaged, try replacing it. Also check the connecting cable. After ensuring that the disk, controller, and connecting cable are working properly, do not rush to use the repair disk created during the operating system installation, or run a file system repair program-the results can be disastrous. Also, don't try to find the recovery program in-does not exist yet. If the information on the disk is of special value, you should first use the disk editor to analyze the status of the control block.
In particular, you need to understand the file system control block format. If you can’t do this yourself, it’s best to call an expert instead of trying to fix it yourself. To check the control block, you need to connect two disks to the computer: the first disk is the bootable working disk, and the second disk is the disk from which you want to recover information. First, connect only the first disk and install. This disk will be used to save files recovered from the damaged partition. Next, install the disk probe editor in the resource kit. Although this editor is far from perfect, he is responsible for all the work of recovering lost files. After making sure that everything on the first disk is normal, shut down the computer, and then connect the second damaged disk to the computer. For successful information recovery, the cluster size and boot sector address should be determined. The first value can be obtained from the boot sector of the partition (of course, if its contents are preserved).
Double-click the left mouse button on the corresponding line in the "Available physical drives" list. Then press the set activity button, keep the read-only switch turned on, and then use the OK button to close the panel.
Then try to read the contents of the master boot record of the disk, which is located in the first sector of cylinder 0 track 0. To do this, select the "Read" line from the "Sector" menu. The "Read Sector" panel appears. In the "Start Sector" field, set the first sector number to zero, and in the "Number of Sectors" field, set the value to 1. Then click the "Read" button. 
The program reads the content of the first sector and displays it in hexadecimal format. Select the "Partition Table" row from the "View" menu to format the disk partition table, and then use the "Execute" button to navigate to the desired partition. If necessary (when recovering files from the extended partition), repeat this process several times. After reaching the boot record of the desired partition, select "Boot Program" from the "View" menu.
It contains all the information about the geometry of the restored partition. In particular, the cluster size in the sector is in the "sector per cluster" field. In addition, the cluster numbers of the primary and standby tables are displayed here (the "cluster to" and "cluster to" fields respectively). But what if the master boot record or the boot record of the required partition is damaged?
However, please note that if you pay attention to the possibility of subsequent recovery from disk damage, you can facilitate this type of work when needed. After installing the operating system, you need to determine and record the size of the cluster immediately, while the boot sector is still intact.
If the size of the cluster is still unknown, it must be determined indirectly or through selection methods. Without going into details, we will only introduce the information required for recovery.
Store information about files in multiple locations on the logical device. The directory contains a file descriptor that contains its name, size, creation date, and the number of the first cluster assigned to it. The file allocation table (from which the file system is named) stores a linked list of all clusters allocated to files. Finally, the files themselves can be scattered across the cluster. This arrangement makes it difficult to recover files in case of any failure. The integrity of the table is especially important: if the table is lost or its contents are partially destroyed, information about the clusters assigned to the file will disappear. As a result, it is very difficult to assemble files from separate clusters only by knowing the contents of the files. Moreover, this work is very time-consuming. Therefore, in fact, the disappearance of the table and its copy means the complete loss of the file.
The loss of the directory will make it impossible to determine the number, name, and exact size of the first cluster assigned to the file. In this case, the consequences are not so catastrophic, because there are many cluster chains in the table, which can easily become files. The file name obtained in this way usually consists of numbers. Please note that if a directory containing thousands of files crashes, after recovery, if the content of the required file is even unknown, it will be difficult to find the required file. All information about files is stored in the so-called master file table. The record contains a set of descriptors with file information, such as name, creation and modification dates, security attributes, and most importantly a list of clusters assigned to the file. If the file is small, it can be stored directly in the record. Therefore, the ability to recover files from damaged partitions largely depends on the integrity of their copies.
If the boot sector of the partition is reserved, it is very simple. In the panel shown in Figure 12, click the button next to the or field. 2. To view the contents of the first sector of the table, select the "Byte" row from the "View" menu of "Disk Probe". The table entry of the description file starts with it. There are also some catalog entries, index entries, and others that we will not cover. Looking at the table, you can find the entries of other system files, such as $, $, $, $, etc.
Set the switch to the position shown in Figure 2. 4. Then fill in the input character field to be searched, and then click the search button. Please be patient, as the search process may take a lot of time.
Please note that you can find the records of the files that need to be restored in the table in a similar way. Because the file name is stored as a character, the radio button must be set to characters when searching. In addition, exhaustive search and ignore cases must be enabled.
It does not include any method of formatting the recorded content. In addition, there is no exact format for this entry in the open document. However, you can find a lot of things on by searching keywords. For example, we managed to find information gathered by the developers of operating system modules. By analyzing the source code of the module used to install the file system on, you can understand the purpose of each field of the record (the author thanks for the help of the record).
It consists of a fixed-size initial segment and a set of attributes that are usually variable in size. To recover files, you only need to know the exact format of the data attributes. As for other attributes, it is sufficient to determine their location and size.
The first four bytes of the description file in the record form the word. In the figure. 3 They are highlighted in red. The next two bytes (highlighted in blue) are the so-called zone offsets. In this case, the offset value is 3 (taking into account the reverse order of the bytes in the word). In the following, we will use hexadecimal numbers.
Used in the process of detecting read or write errors. It consists of two byte words. The number of words is stored in the record with an offset of 16. 3The fixed area size box is highlighted in purple. The value 13 is stored here, so the area starts at offset 3 and expands to 3 + (2 * 13) = 3. The first four bytes of the attribute area define the type, and the last four bytes define the size. For example, an area with an offset of 25 is followed by an attribute of type 11. This type and Type 3 of the following attributes are highlighted in red (the size of the attribute is highlighted in blue). The length of this attribute is 49 bytes, so the next attribute (type 31) will start at offset 79.
For file recovery, the most important are the attributes of types 31 and 81, the first to store the file name. It should be used to search for records describing restored files. The second attribute, type 81, stores a list of clusters assigned to the file or the file itself. We will tell you more. 
It can be seen from the figure that the attribute type equal to 81 is stored in the record, and the offset is 113. Since this value is located in a four-byte field with an offset of 4 from the beginning of the attribute, the data attribute occupies a Ambrose total of 8 bytes. Usually, records only contain small files. They store the length of a file located somewhere on the disk. The length of the $file in this example is 71 bytes.
In order to determine the exact location of non-resident files on the disk, you need to track a string of so-called virtual cluster number blocks, or blocks for short. The offset of the start of the chain is stored in a two-byte field, 22 bytes from the start of the data attribute. In the described case, the indicator is 41, and the offset of the block area from the start of recording is 20. In the figure. In Figure 5, this area is highlighted with a bold vertical green line.
It consists of one or more blocks called extension areas. The size and location of each extension area is described in the block. Depending on whether the file is segmented, the area can contain a block or a group of blocks. The size of the block is variable, indicated by the first byte.
The block format deserves a concrete example. The first field is one byte in length and stores the number of clusters allocated to the file range. The second three-byte field contains the number of the first cluster. In this case, the first extent of the $ file has 22 clusters, and the first cluster number of the first extent is 2789. This is how we determine the size and location of the first extension of the file.
In order to determine the first cluster of the second extension area, the offset (including the sign) specified in the second block must be added to the address of the first extension area. In this case, the second extent is in cluster 287 9 + 22 = 287. The second range is 825 clusters long. You can define the size and location of all extension areas in the file. The block list is closed with zero bytes.
Small files are placed directly in the records describing this file to reduce access time. If the byte offset 8 from the start of the data attribute contains a zero value, you don't need to track the blockchain. This means that the file is located in the data attribute. In this case, the offset of the resident data (ie file) is written in a two-byte word with an offset of 15 relative to the beginning of the data attribute, and the size is in a two-byte word with an offset of 11. Containing resident data attributes, we have prepared a small file named, which contains text strings. Then, using the "disk probe", we found the record created for this file (Figure 6). Equal to zero, so we are dealing with resident attributes.
Relative to the beginning of the attribute, the file size is 1 byte.
Now, with the above knowledge about the internal structure of the system block, you can start recovering files from the damaged partition of the file system.
When you know the name of the file to be restored, you need to find the corresponding entry in. You can use the "Disk Probe" in the "Search Sector" row in the "Tools" menu to complete this operation. Next, you should find the attribute in the record and determine whether it resides.
If the attribute is permanent, you need to save the sector containing the record as a file and save it on the working hard disk or floppy disk. This can be done by using the "Save As" line on the "File" menu of "Disk Probe". After that, you should cut off the required part of the data and save the result in a new file. For example, in the for -, it is not difficult to do this.
For non-resident properties, more work will be done.
You need to determine the location and size of the restored file range. Next, use the "disk probe" to read the range data and save it to a file on a healthy disk. Also remember that the "disk probe" specifies the number of sectors to be read or written, and the "" block specifies the number of clusters allocated for the extent. Therefore, appropriate recalculation must be performed.
After restoring all extents, merge them into one file (for example, use the command with the / option). Then set the correct file length obtained from the 31 field of the attribute. In the partition, the same procedure can be used to perform this operation.
Unfortunately, in practice, restoring a large number of files is very time-consuming. The most difficult part is the manual processing of the blockchain, which can be very long. You have to spend hours using a calculator to convert decimal numbers to hexadecimal and vice versa, and perform various necessary arithmetic operations to determine the size and location of the recovered file range. Therefore, we usually use small self-made programs that perform the most time-consuming operations in semi-automatic mode.
When using attributes to describe files, this article completely bypasses the recovery of files with a large number of fragments. If the hard disk has been used for a long time and has been filled several times, the disk will contain a large number of highly fragmented files. Such content cannot be restored under this article. Well, in general, the considerations are very superficial, and people who want to restore files based on this article may be surprised. Kit 21.9.
-3101 Introduction to Hard Disk Data Recovery SALVING OF FLOATING DRY DOCK AFDM-2 1965 U.S. NAVY DOCUMENTARY FILM 79014