China DOS Union

Although current storage technologies are becoming more and more advanced, and new storage tools such as ZIP, LS120, CD-RW, etc. are popularizing, for various reasons, all these cannot replace the floppy drive and floppy disk that have accompanied the development of PCs since the day PCs were born. Floppy disks are convenient, easy to carry, and inexpensive, and still occupy an important share in the storage market. The most important point is that almost every PC now is equipped with a 1.44M floppy drive, and the floppy disk is probably still the most convenient choice for transferring and backing up a small amount of data. This article will comprehensively introduce content such as floppy disk data recovery and repairing bad floppy disks, and hope to be helpful to you.

### I. Introduction to Floppy Disk Data Structure

The currently commonly used is a 3.5-inch 1.44M floppy disk. After a floppy disk is formatted, it is logically divided into:

Track (TRACK): Several concentric rings divided on the disk;

Head: Divided into two sides, 0/1;

Sector: The area on the track for storing data, which has several parts.

The standard formats of 3.5" disks are 720kB (80 tracks, 9 sectors per track) and 1.44MB (80 tracks, 18 sectors per track), and the standard formats of 5" disks are 1.2MB (80 tracks, 15 sectors per track) and 360kB (40 tracks, 9 sectors per track).

The most commonly used 1.44M 2HD floppy disk now has 80 tracks (that is, 80 concentric circles), each track is divided into 18 sectors, and each sector is further divided into 512 bytes. The 0 side 0 track of the floppy disk is very important. The first sector is the boot information, the second and third sectors are the starting sectors of the first file allocation table (FAT), and then there is the data area. Each formatted disk with files established a file directory table in the disk, recording useful information about all files on the entire disk, so it is beneficial for us to understand its structure. In the file directory table, each file occupies 32 bytes (when read with PC-TOOLS or DEBUG, it occupies two lines). The meanings of each byte are as follows:

Bytes 0-7: File name, 8 bytes in total. If less than 8, filled with 29. If the first byte is 00, it means this item is not used. If it is E5, it means this item has been deleted.

Bytes 8-10: File extension, 3 bytes in total. If there is no extension or less than 3, filled with 20.

Byte 11: Represents the file attribute. The specific meanings are: 20 is an archive file, 01 is a read-only file, which cannot be modified or deleted. 02 is hidden, which cannot be found by the DIR command. 04 is a system file, which cannot be found by the DIR command. 10 means this item is a subdirectory, not a file. 28 means this item is the volume label of the disk, that is, the name of the disk, not a file.

Bytes 12-21: A total of 10 reserved fields, not used.

Bytes 22-23: The time when the file was created.

Bytes 24-25: The date when the file was created.

Bytes 26-27: The first cluster number occupied by the file, that is, the starting cluster.

Bytes 28-31: A total of 4 bytes, which is the length of this file.

The position and length of different disk directory tables in the disk are also different. The 360k disk directory table is in the relative 5th to 11th sectors of the disk, a total of 7 sectors; the 1.44M disk is in the relative 15th to 28th sectors of the disk, a total of 14 sectors. Mastering the structure of the directory table, we can use it to do some work. For example, if a file is mistakenly deleted and the disk has not been written to otherwise, and there is no other software to recover, we can modify the first byte of this item in the directory table, change E5 to something else, and the mistakenly deleted file can be recovered.

### II. Recovering Disk Data with Tool Software

Generally speaking, the situations where a floppy disk is damaged and data is lost can be divided into 3 major categories:

One situation is that the zero track is bad, and the drive letter cannot be seen and the directory cannot be listed. The error message displayed on the screen is generally:

"General Failure error Reading drive A Abort, Retry, Ignore?"

The second situation is the most common, that is, a certain part of the floppy disk is damaged. The directory can be listed, but a certain file or several files cannot be read or the file is damaged after reading. The error message displayed on the screen is generally:

"Sector not found error Reading drive A Abort, Retry, Ignore? or Data error Reading drive A Abort, Retry, Ignore?"

The third situation is physical damage, such as mildew on the disk, scratches on the disk, magnetic powder falling off, etc.

To recover floppy disk data, some tool software is needed. The following introduces commonly used floppy disk data recovery software one by one:

#### 1. HD-COPY

HD-COPY is a disk copying program written by a German. The main program is only more than 40k, but it has very powerful functions, including formatting floppy disks, expanding floppy disks, repairing bad floppy disks, saving floppy disk information, reading bad floppy disks, compressing files, cleaning the magnetic head of the floppy drive, etc. Its function of reading data from bad disks is very strong. It can repeatedly read bad tracks (the maximum number of times can reach 100 times). When it is confirmed that the information of the bad track cannot be read out, it will leave the damaged part aside and save the useful parts as much as possible. The usage of HD-COPY is very simple:

When HD-COPY is working, it will read all sectors from track 1 of side 0 and track 1 of side 1 of the floppy disk to track 79 of side 0 and side 1. When encountering a bad track or bad sector, it will repeatedly read the track or sector many times to read out as much information as possible. So no matter what damage the floppy disk has suffered, we can use it to read the faulty floppy disk and then copy the information to a good disk. When entering HD-COPY, there are two rows of small dots in the Source (source disk) box in the upper left corner of the screen, where the upper row represents tracks 0-79 of side 0 and the lower row represents tracks 0-79 of side 1. When you insert a floppy disk and select Read (read), it will use R to replace the small dots to indicate that it is reading a certain track and the track has been read, and E indicates that there is an error in the sector of a certain track. After reading the source disk, insert the destination disk into the drive, move the cursor to Write (write) and press Enter. At this time, there are moving W or V covering the small dots in the Destination (destination disk) box to represent "write" or "verify".

If only the zero track is bad, then the possibility of data recovery on the floppy disk is very high. Usually, as long as HD-COPY is used to make an image of it and then store the image on another good floppy disk, the data can be recovered. For the situation where the data area of the disk is damaged, HD-COPY can read as much as possible. If it is a text file, the recovered data is still very valuable, but for files such as exe and dll, it is of no practical significance after recovery.

#### 2. Norton's NU Software Package

The disk tool software package Norton is a tool software specially used to repair disks. It contains several programs that are very useful for recovering floppy disk data.

##### (1) NDD

Put the floppy disk that needs to be repaired into drive A, start NDD, select Diagnose Disk in the main menu, then select drive A and press Enter. NDD will analyze the boot record, file allocation table, directory structure, lost clusters and other information of the disk. When a bad sector is found, it will display the wrong place and the reason, and ask if you want to correct this error? Press Y, and the screen will display whether to create an UNDO file, skip this step, or exit NDD. Select Skip (skip), and the disk doctor will start to repair the faulty sector. If the first FAT table is damaged, it will automatically write the second file allocation table back to the sector where the first file allocation table is located, and all files on the disk can be read out. If the bad sector is in the directory area, some files or subdirectories may not be found when listing the directory. NDD uses DIR00000─DIRXXXXX to represent lost subdirectories and FILEXXXX.－DD to represent files; when the bad sector is in the data area, part of the file stored in this sector may not be repaired. One sector can store 512 bytes of content. Pay attention to the screen displaying XXXX lost clusters in XXX chains and asking: "Do you wish to save lost chains as files?" (Do you want to save the lost chains as files?), you should select Save. If you select Detele, the lost information will be completely deleted and cannot be recovered again. The next step is to do Surface Test (disk surface test) to check if there are bad tracks (cylinders) on the disk surface. You can choose to test or skip according to your needs. If you want to continue using a disk with some bad tracks, you can use it to help you mark the bad tracks so that DOS can bypass these bad tracks when reading and writing.

NDD is a very professional disk doctor with a high IQ and can repair most errors on the disk. The use process of NDD is quite "foolish". Generally, after NDD is started, as long as you select the drive letter of the floppy disk that needs to be repaired, and then press Enter all the way, the repair work can be completed. NDD is mainly used for disk file errors, slight damage to the disk surface, disk system errors, etc., and has very powerful functions. But it has a limitation that it can only recognize standard format floppy disks. If the floppy disk to be repaired is not a standard format, NDD will automatically modify it to a standard format, which may lead to complete data loss. Therefore, NDD cannot be used to repair non-standard format floppy disks. Files on non-standard format floppy disks need to be saved by tools such as HD-COPY.

##### (2) DISKEDIT

Disk Editor in Norton has the function of reading and writing absolute sectors. If you are very familiar with the storage law of disk data, you can use this software to directly recover some data. After running DISKEDIT, click the (O) object on the menu with the mouse, click (D) drive, select (P) physical disk, then click floppy drive A:, and the physical sector area will appear. The default value for reading absolute (physical) sectors is side 0 (head) track 0 sector 1. Because the data area generally starts from sector 16 of track 1 of side 0, we can look for our own files from sector 15 down. You can use the PgUP, PgDn keys or the mouse to turn pages up and down. If the file is a text file, etc., its content will be displayed on the right side of the screen; when you see the sector with the content you need, you can save it to a file: select (P) physical sector on the screen, enter the starting sector and the number of sectors, click OK, then select (W) write object to in (T) tools, select (F) file in the screen that appears and click OK. Note that the file must be saved on the hard disk.

##### (3) DISKTOOLS

DISKTOOLS.exe is also a disk repair tool in the NORTON toolbox. Its biggest advantage is that it can perform low-level formatting on the floppy disk without losing data, which is very useful for saving bad disk data;

The main program of the Chinese version of DISKTOOLS.exe is only 54kB, but like the above two software, it also needs the NORTON system files nlib200.rtl and Chinese font china16.fnt to cooperate to run normally. It provides 4 functions: making the disk bootable, recovering after using the DOS recover command, regenerating a defective disk, and marking a cluster. Among them, regenerating the disk is safe low-level formatting. This function is very useful for saving files on bad disks, especially when there are no other backup floppy disks. The specific use method of DISKTOOLS is very simple, so it will not be repeated here.

##### (4) TS

There is also a little-known tool in the NORTON toolbox: TS.exe. The function of this software is to find the mistakenly deleted or lost data by sector, and then save the found data to another file as needed.

#### 3. PCTools 5.0 and DEBUG

PCTools 5.0 is a relatively commonly used disk tool software. There is only one file pc.exe, about 169kB in length. It mainly has two major functions: file service and disk service. Its disk service function mainly provides disk copying, deletion, comparison, renaming, verification, editing and initialization, as well as file undelete functions. Among them, the disk initialization function is low-level formatting (simultaneously high-level formatting) of the floppy disk, which can completely delete disk files. Even if an undelete tool is used, it cannot be saved. But it is precisely this low-level formatting that can solve some problems that cannot be solved by high-level formatting. Moreover, after low-level formatting, high-level formatting is not required, and a relatively delicate verification is adopted. Clusters that cannot pass the verification have been marked as bad clusters. The floppy disk can be used with confidence after initialization.

In addition, DEBUG built into DOS is also a software that can perform physical-level reading and writing on the floppy disk, and is a commonly used tool for some top experts.

#### 4. Scandisk

For a floppy disk with problems, we can simply try to repair it with tool software. When we cannot read the floppy disk data, it is a good idea to try Scandisk built into Win98. Although its function is not very powerful, it is easy to find and use, and fully supports Microsoft's long filename format. We only need to select the drive letter of the target disk and perform a complete surface test (surface test). If there is any prompt in the middle, just select yes or next. The program will automatically move the data from the bad track or sector to the intact position. If lucky, the repaired disk will be almost the same as the undamaged one.

In addition, when the disk space is lost for no reason, or there are messy character filenames or super large files, Scandisk can also deal with such problems. Usually, the reason for such a situation is abnormal loss of disk clusters. A cluster is the smallest unit for disk reading and writing. On a 1.44M floppy disk, it is equivalent to a sector, which is 512 bytes. If a data segment is occupied but not marked in the FAT table, data loss will occur; conversely, if the FAT marks an empty data segment as a file, the space will be lost for no reason.

#### 5. Badcopy

Badcopy is a tool software compiled by Ren Liang for copying and saving data of floppy disks with damaged tracks. Badcopy99 can stably work on Chinese and English Win95/Win98/Win2000 and WinNT platforms. The entire software is a little more than 300K, and it is a "green software" that does not need to be installed and can be executed directly.

All the copying and repairing functions of Badcopy99 can be realized on the homepage of the software. First, determine whether you need to copy files (can be multiple files) or copy the entire folder (including subfolders inside). There are two options, File and Folder, under for you to choose; then select the files or folders to be copied, and then tell Badcopy which folder (Target Folder) to save the saved data in. You can also select it by browsing. When everything is ready, press the Copy button. Badcopy will automatically try to read each byte of data desperately. If it really can't, Badcopy will use intelligent filling to complete the data. All these processes are transparent. The copying and repairing progress will be displayed under Target Folder, and then the number of copied files and the amount of intelligent filled data will be displayed.

In the page, you can freely customize some parameters of Badcopy. For example, whether to display hidden or system files, whether to automatically perform intelligent data filling, whether to retry, and the size of each data block (when the repair data effect is not ideal, you can try to adjust the parameters. If the data is precious, you can set the Block Size relatively small, so as to save your data to the maximum extent; if you pursue speed, set it larger appropriately). There are also and other pages, which provide some common file operation functions. The use of this software is very simple, and you can know it at a glance.

#### 6. Disketer

This software is called HD-Copy under Windows and is a good tool specially for floppy disk operations under Windows at present. It has a standard Windows interface, is easy to use, and has powerful functions. But this software has a big limitation. To use the super function of Disketer, you must follow some special requirements of it, that is, you must use the formatting function of Disketer and then use Disketer to copy and delete files to the floppy disk. Then when the floppy disk is damaged later, Disketer will be useful. That is, select "Tools/format" in the main interface to format, then click the "Open" on the tool bar to open the disk, click "Add" to add files to the disk or "Del" to delete files. This affects the wide application of this software to a large extent. The following is to specifically talk about the function of Disketer to repair the disk:

Repair the zero track: If the disk can be opened but cannot be written or deleted, it can be judged that the zero track is damaged. Select "Tools/Diskservice". Select "Repair #0 sector", and it can be processed into a normal floppy disk, which takes about 30 seconds. Also, like Badcopy, Disketer can read files in bad tracks on the floppy disk or hard disk. It automatically gives up bad tracks in units of 512Bytes. Click "File/repair file", enter the bad sector number (the bad sector number is displayed during the copying process of Disketer, write it down and enter it here) after "Sector number"; you can enter multiple and add them with the "Add" button; then enter the path and name of the file to be read and the path and name of the repaired file to be stored; after setting, press the "Repair" button to start data recovery.

#### 7. Other "Unorthodox Methods"

Sometimes, in order to save important data on the floppy disk, we can try everything. Some software is not used to repair disks on the surface, but we can also try it. Maybe it will have amazing effects. For example:

Ultra Edit. Run Ultra Edit, insert the disk, and select the file you want to save. Here, it is generally in "HEX" mode (except for text files). If it can be read out, you only need to do "SAVE AS" here, give it a name, and save it. Most of the time, Ultra Edit will prompt "Error reading file:A:\filename.ext". If you are still not discouraged, please press "Retry" and try several times.

WinZip. Insert the disk, open Windows Explorer, select the file you want to save, right-click to open the shortcut menu, select "Add to Zip" (if you have installed WinZip), enter the target path and file name in "add to archive" (must be placed on the hard disk), click "Add", and the damaged file may be packed into the compressed package! Then you just need to "EXTRACT" it.

### III. Other Problems Encountered in Recovering Floppy Disks

The situation that the data on the floppy disk cannot be read is very complex. In addition to reasons such as bad tracks, the tool software mentioned above can be used to save it. There are also the following situations that may lead to the data on the floppy disk not being read.

#### 1. Reading of Non-standard Capacity Disks

After using software such as HD-Copy to expand the capacity of the floppy disk, the direct consequence is that it is very likely that it cannot be read on other machines. For example, if we use HD-COPY software to format a 3.5-inch 1.44MB high-density floppy disk into 1.722MB, when reading and writing under DOS, the prompt "sector not found reding drive b (or a), abort, retry, ingore, fail?" often appears. This is because each side of the 1.77MB disk has 82 tracks, and each track has 21 sectors, that is, 82×21, while the 1.44MB disk is 80×18. It can be seen that the 1.722MB disk is relatively irregular. To read and write such disks normally, the following methods can be adopted:

Find a special small software named 800.EXE that is resident in memory, which supports reading and writing of irregular floppy disks. It can also be solved by loading the DOS external file DRIVER.SYS. That is, add a line of statement in the CONFIG.SYS file:

DEVICE=DRIVER.SYS /D:/F:9

Among them:

/D: The number in here refers to the physical floppy drive. 0 represents drive A and 1 represents drive B.

/F: 9 The number 9 here can be replaced by other numbers. The meanings of each number are as follows:

0: Represents a single-density 160KB/180KB or 320KB/360KB floppy drive; 1: Represents a 1.2M floppy drive; 2: Represents a 720KB floppy drive; 3: Represents an 8-inch single-density floppy drive; 4: Represents an 8-inch floppy drive; 5: Represents a hard disk; 6: Represents a tape drive; 7: Represents a 1.44MB floppy drive; 8: Represents an optical drive; 9: Represents a 2.88MB floppy drive.

However, the simplest method is that if there is an option for a 2.88MB floppy drive in the CMOS configuration of the microcomputer, then just configure the floppy drive as 2.88MB.

#### 2. Treatment of Moldy Floppy Disks

For a floppy disk that has become moldy, if there is no important data, of course, it should be thrown away without hesitation. But for some floppy disks that store important data, we still need to find a way to repair them.

For a slightly moldy disk, dip a piece of absorbent cotton in a little tape head cleaner, gently wipe from the head reading and writing port, and the magnetic mold spots can be wiped off. Then dry the liquid beads on the disk surface with a clean absorbent cotton. For a disk with relatively serious mildew, first take the magnetic sheet out of the envelope, place it on a flat and clean white paper, then use the tape head cleaner to wipe the entire disk surface, and dry the cleaning agent liquid beads with a clean absorbent cotton. Then change to a white paper and clean the other side. After the disk is cleaned, reinsert it into the envelope. Using absolute alcohol (chemically pure or analytical pure) and acetone instead of the tape head cleaner also has a good effect. It should be noted that metal appliances should not be used during the operation, and it is best to wear thin gloves to avoid direct contact with the disk. Most of the disks processed in this way can recover most of the data.

#### 3. Floppy Drive Failure Leading to Failure to Read the Disk

If there are phenomena such as being unable to read most or all of the floppy disks, being unable to format, and having abnormal sounds, it is very likely that the floppy disk data cannot be read normally due to a floppy drive hardware failure. There are many possibilities, but it is definitely a problem with the floppy drive hardware. It is recommended to replace it. In addition, there are often situations where a floppy disk cannot be read on one floppy drive but works fine on another machine.

Finally, remind everyone that the reliability of floppy disks is very poor. Do not store important data only on one floppy disk. For floppy disks with important data, be sure to back them up and write-protect them to prevent data loss due to misoperation.

Floppy Disk Repair Toolkit

First of all, you need to prepare a toolkit - a 3.5" floppy disk. This floppy disk must be a well - known brand with good quality, preferably a new one. Of course, this is just for easy carrying. When actually using it, you need to copy the files to the hard disk.

First, the famous NDD in Norton Toolkit - this is a very professional disk doctor with a high IQ, which can repair most errors on the disk;
Second, pctools 5.0, its disk service functions such as disk initialization, disk editing, disk verification and other functions are very useful;
Third, disktools.exe, it is also a tool in Norton Toolkit. Its biggest advantage is that it can perform low - level formatting on the floppy disk without losing data, which is very useful for saving bad disk data;
Fourth, HDcopy (version 2.3a and above), its low - level formatting function is relatively strong, which is very useful when repairing the 0 track, and its fast disk copying function can also be used to save files on bad disks;
Fifth, the extremely powerful zero track repair tool newdisk.exe, which can rebuild a new zero track for the floppy disk.
The following introduces the specific use:
NDD - Taking NDD in NOROTON 8.0 Chinese version as an example, this tool has four files: main file ndd.exe (97KB), Norton system file nlib200.rtl (199KB), Chinese font library china16.fnt (256KB), and help file ndd.hlp of NDD. The use process of NDD is quite "fool - proof". In general, after NDD is started, as long as you select the drive letter of the floppy disk to be repaired, and then press Enter all the way, the repair work can be completed. Of course, occasionally there will be a need for backup, then prepare an empty disk for backup. NDD is mainly used for disk file errors, slight surface damage of the disk, disk system errors, etc., and has very powerful functions. However, this smart doctor is a bit rigid - it can only recognize floppy disks in standard format. The standard formats of 3" disks are 720KB (80 tracks, 9 sectors per track) and 1.44MB (80 tracks, 18 sectors per track). The standard formats of 5" disks are 1.2MB (80 tracks, 15 sectors per track) and 360KB (40 tracks, 9 sectors per track). If the floppy disk to be repaired is not in standard format, NDD will automatically modify it to standard format, which may lead to data loss. Therefore, NDD cannot be used to repair non - standard format floppy disks. Files on non - standard format floppy disks need to be saved with other tools.
pctools 5.0 - This is a relatively commonly used tool software. There is only one file pc.exe, with a length of 169KB, in English interface (there is a Chinese - translated version, but it needs Chinese character environment). It mainly has two major functions: file service and disk service. The file service function mainly provides functions such as file copying, moving, deleting, renaming, verification, editing, etc. The disk service function mainly provides disk copying, deleting, comparing, renaming, verification, editing and initialization, as well as file undelete and other functions. Among them, the disk initialization function is low - level formatting (and high - level formatting at the same time) of the floppy disk, which can completely delete disk files, and even with the undelete tool, it cannot be saved. But it is precisely this low - level formatting that can solve some problems that cannot be solved by high - level formatting. In addition, after low - level formatting, high - level formatting is not required, and a relatively delicate verification is adopted. Clusters that cannot pass the verification have been marked as bad clusters, and the floppy disk can be used with confidence after initialization. It should be noted that the initialization function of pctools 5.0 can only format floppy disks in standard format, does not support special formats, and files on the floppy disk cannot be recovered after initialization. Therefore, these two points need to be noted.
Chinese version of disktool.exe (54KB) - It, like NDD, also needs Norton system file nlib200.rtl and Chinese font library china16.fnt (both in one toolkit, one set is enough), and also has a help file. It provides four functions: making the disk bootable, recovering after using dos recover command, regenerating a defective disk, and marking a cluster. Among them, regenerating the disk is safe low - level formatting. This function is very useful for saving files on bad disks, especially when there are no other spare floppy disks. As for the use, it is too simple, so I won't talk nonsense.
HDcopy - It is composed of three files in total, but I only kept the main file HD - COPY.EXE (45KB). It was originally a disk copying tool, generally used to make multiple copies of a floppy disk. However, because of its strong reading ability (it will repeatedly read the bad area that cannot accurately read data, and will give up only if it cannot accurately read data 20 times), and it supports a variety of special format floppy disks, it can be used to save files on bad disks. The operation method is to copy the files of the bad disk to a good disk. I won't talk about the specific operation. Although it is in English interface, the words are very simple, and you can translate it with any Chinese - English dictionary. Oh, I almost forgot, HDcopy has a function of formatting the floppy disk, which is also a formatting function of low - level formatting at the same time. And its low - level formatting ability is stronger than that of pctools 5.0. It can be used to repair floppy disks with more serious damage to the 0 track. When the standard format cannot be repaired, a special format method of changing the number of tracks and sectors per track can be used to repair the 0 track. It seems that HDcopy has no shortcomings and is all - powerful, but it is not. Its biggest shortcoming is that the verification is rough. It is often the case that after the verification is passed, dos or windiws cannot read out. Therefore, when using the special format method to repair the 0 track, it is best not to modify the number of sectors per track, only change the number of tracks, and then repair it with NDD. The floppy disk repaired in this way is still in standard format. Then, what if the 0 track still cannot be repaired by the above method? Don't forget, we still have a tool not used!
NEWDISK - Its function is to rebuild the zero track on any track. The following introduces the command line usage method of NEWDISK: NEWDISK . The track number refers to the track number to be swapped with the 0 track. For 1.2M and 1.44M floppy disks, it can be selected from 1 to 79. When the command line is empty, it is automatically defaulted to 39. Type NEWDISK and press Enter, insert a floppy disk with bad 0 track that cannot be formatted, and use the FORMAT command again, and it can be carried out normally. For easy use, NEWDISK not only provides options /R, /U, /Q to unload from memory, but also prepares a flexible switch - NEWDISK is activated only when the Scroll Lock light is on.

Good post! Keep it up!

Benefited a lot and am very grateful.

Continue

But!
　　NEWDISK
Where to download it then?!

http://www.hld.ln.cninfo.net/download/xtfiles/newdisk.exe

Can't download anymore