Many computer users have seen or heard that when a hard disk is infected with the so-called "logical lock," some computers cannot be booted using floppy disks, hard disks, or optical discs. So, what exactly is a "logical lock"?
The so-called "hard disk logical lock" is made using a flaw in some versions of DOS. It uses the technology of "circular partition tables," making some versions of DOS with this flaw unable to be booted by any device, including mobile devices such as floppy disks. When DOS starts, the system automatically searches for information about each partition on the hard disk, such as type and size, so that the system can recognize the hard disk, respectively assign it as drives C, D, E, F, etc., and allow the user to perform various operations on it. And the "logical lock" precisely makes use of this point. By modifying the partition table of the hard disk to make the partition table circular, that is, pointing the first logical disk of the extended partition to itself, it causes a dead loop when some versions of DOS start to search for partitions, making it unable to boot.
It can be seen that this is actually caused by a flaw in the startup of DOS. It is said that as early as 1992, an anti-virus expert named Mike discovered this problem and reported it to the manufacturers of the relevant versions of DOS, such as IBM, which produces PC-DOS, Novell, which produces DR-DOS/NovellDOS, and Microsoft, which produces MS-DOS, etc. Soon after, IBM, Novell, and other companies successively announced that their new versions of DOS had completely solved this problem, but only Microsoft, which owns MS-DOS, ignored it, resulting in the new versions of MS-DOS, such as 6.x, 7.x, etc., still having this problem.
However, since Microsoft's MS-DOS is used the most widely, its impact and harm are also the greatest. Once a user's hard disk is locked by a "logical lock," the boot disks of various Microsoft operating systems, such as MS-DOS 5.x/6.x, MS-DOS 7.x/8.0 (Win9x/ME), etc., cannot boot, creating the illusion of a hardware failure, and even many experts are at a loss. Since this phenomenon is very terrifying and will lead to the computer being unusable, many people are frantically looking for prevention and solution methods. In fact, it is not difficult to solve. Several solutions are introduced below.
### Using a non-MS-DOS operating system to boot
As can be seen from the above, the "hard disk logical lock" mainly affects Microsoft's MS-DOS system. Therefore, using other versions of DOS to boot is fine. To this end, I specially conducted boot tests on several practical high-version DOSes, such as MS-DOS 7.10 (Win9x), PC-DOS 7.10, DR-DOS 7.05, ROM-DOS 7.10, FreeDOS beta8, and PTS-DOS Pro2000, in the case where the hard disk is locked by a "logical lock." The results are as follows:
PC-DOS 7.10 boot disk: boots normally;
DR-DOS 7.05 boot disk: boots normally;
ROM-DOS 7.10 boot disk: boots normally;
FreeDOS beta8 (7.10): displays an error on the hard disk when booting and boots normally;
PTS-DOS Pro 2000 (6.90): boots normally.
Note: The above various versions of DOS are all very stable and all support FAT32 partitions and large hard disks. Among them, ROM-DOS 7.10 also fully supports long file names locally and has very good compatibility.
Therefore, any of the above-mentioned DOS boot disks can be used to boot a hard disk locked by a "logical lock." After booting, drives such as C: are invalid, but various disk partitioning software, such as Norton Disk Editor 2002, Norton Disk Doctor 2002, and the FDISK program built into DOS, etc., can all display the locked hard disk. At this time, tools such as DISKEDIT mentioned above can be used to view/manually repair the hard disk, etc., or some software can be used for automatic repair, such as NetResq, which has the function of automatically removing the "logical lock," and the data on the hard disk will not be damaged at all.
### Using a repaired MS-DOS boot disk to boot
Although the MS-DOS boot disk cannot boot the computer when the hard disk is locked in the normal state, since this is only a bug in the IO.SYS startup file of MS-DOS, as long as this bug is repaired, the MS-DOS boot disk will not be affected by the "logical lock" and can boot normally. However, even when repairing the bug, the correct method should be used. Some people have mentioned the method of modifying the hard disk partition mark "55AA" in IO.SYS to solve the problem. In fact, this method is very bad. Because this method actually makes IO.SYS completely ignore the existence of the hard disk, that is, by skipping the hard disk to boot from a floppy disk. In this way, no matter whether the hard disk is locked or not, the hard disk cannot be recognized after booting with this boot floppy disk, so this boot disk cannot be used as a normal MS-DOS boot disk. On the contrary, if the bug in IO.SYS is repaired correctly, after booting with this floppy disk, if the hard disk is good, it can be recognized normally, and even if the hard disk is locked by a "logical lock," further repair operations can be carried out by using the boot disks of PC-DOS, DR-DOS, ROM-DOS, FreeDOS, PTS-DOS Pro, etc., as mentioned in the above method (that is, "using a non-MS-DOS operating system to boot"
. Some people have also mentioned using some low versions of MS-DOS, such as the boot disk of version 3.2, to boot the computer. But this obviously has many drawbacks. First, it is very difficult to find the old version of DOS. Second, due to its very low version, it has very few functions and very poor compatibility. Third, these low versions of DOS themselves do not support large hard disks (not even supporting 32M), logical partitions, etc., and may even cause real damage to the hard disk. Moreover, versions such as MS-DOS 3.2 even do not recognize 1.44M floppy disks. It can be seen that the method of using the low version of MS-DOS to boot is not very feasible. Therefore, it is very important to use a good method to correct the bug in the IO.SYS of the high version of MS-DOS. Taking the boot disk of MS-DOS 6.22 as an example, it is only necessary to use any hex editor (such as PCTOOLS, etc.) to find the hexadecimal string "07 72 03" in the IO.SYS file and replace the final "03" with "06". The same method can be used for other versions of MS-DOS. In this way, the Microsoft MS-DOS boot disk can also boot normally when the hard disk is locked by a "logical lock" like various other versions of DOS.
The above-mentioned methods are all the most direct methods to solve the "hard disk logical lock" (that is, "using a DOS boot disk that is not affected by the 'logical lock' to boot the computer"
, and also the best methods. Therefore, as long as a boot disk as mentioned above is made (such as a PC-DOS 7.10 boot disk, a ROM-DOS 7.10 boot disk, a FreeDOS boot disk, or a repaired MS-DOS boot disk, etc.), it will be fine. It can be used as a normal boot disk at ordinary times, and when the hard disk is locked, it can be used to boot and solve the problem.
Some people have also mentioned other "methods," such as hot swapping the hard disk, low-level formatting with DM, etc. These are not only troublesome and dangerous but may also cause damage to all data on the hard disk. For example, after hot swapping the hard disk (which requires opening the case and removing the hard disk, and then reinstalling the hard disk after booting, which is very troublesome and dangerous), even if it is successfully booted from a floppy disk, the hard disk will completely not be recognized at this time, and even various hard disk tools cannot recognize it. If DM is used to skip the BIOS to low-level format the hard disk, all data on the hard disk will be lost completely and cannot be recovered, resulting in a very large loss. It can be seen that methods such as hot swapping the hard disk are not practical and feasible.
Therefore, as long as a good solution is found and corresponding operations are carried out, the so-called "hard disk logical lock" can be easily solved. Everyone might as well give it a try.
Author: Wengier
