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Troubleshooting Hard Disk Drives

This section includes troubleshooting information for a wide variety of hard disk problems. Hard disk problems can range from outright failure to data corruption to problems with setup. Since they are so important--they hold your main data--hard disk problems can be particularly unnerving, and I have tried to include as much information as possible to help you with problems related to them.

You should not hesitate to contact your hard disk drive manufacturer's technical support department if you need them. In my experience these companies have above-average technical support, and there are sometimes problems specific to certain kinds of drives that I do not know about and therefore are not listed here.


There is an apparent failure of the hard disk; the hard disk is not bootable nor accessible at all


Explanation: There is a general failure of the hard disk. Either an error message is being displayed indicating a failed disk at boot time, or some other wholesale problem is either preventing access to the hard disk, preventing it from booting, or making it impossible to detect the drive in the BIOS setup program. If the drive won't boot but is accessible after booting from a floppy, look here.


Diagnosis: There are many different causes of apparent hard disk failures. Sometimes the problem is the disk itself, but just as often it is a configuration or other problem.





I had a hard disk that was functioning properly in one PC, but when I moved it to another PC or upgraded the motherboard, it stopped working, or the data on it was not accessible


Explanation: You have a hard disk that was working properly in an existing PC but stopped working when installed in a new PC (or after upgrading the motherboard or making another similar change).


Diagnosis: There are many different reasons why this sort of thing can happen. Often, it is simply an installation or configuration problem that can plague any PC after it has been worked on. However, it is also possible that there is an incompatibility between how the two BIOSes access the disk. In particular, BIOSes can use different translation modes to access the disk sectors. So it may be the case that the new PC is referring to the sectors on the disk in a different order than the old one was, which can cause many problems. The use of dynamic drive overlays can also complicate matters, especially if you are moving from a system that does not have native BIOS translation support, to one that does.





The hard disk will not boot, but is accessible after booting from a floppy disk


Explanation: The hard disk drive is refusing to boot when the system is started. After a bootable floppy disk is used, however, the hard disk can be seen and accessed using disk utility software such as FDISK or Partition Magic.


Diagnosis: Usually, if the disk can be detected in the BIOS setup and accessed after booting from the floppy disk, this implies a software problem of some sort. A common one is a boot sector virus. Another common problem is trying to boot up a new hard disk before partitioning and formatting it.





The hard disk won't autodetect in the BIOS setup program


Explanation: The hard disk drive cannot be detected using the autodetect utility within the BIOS setup program. Usually, the BIOS will pause for a long time while it searches for the drive, and then will return saying that the drive was not found.


Diagnosis: There are many, many different reasons why a hard disk may not be visible to the BIOS setup program. They usually fall into two major categories: problems with configuration (how the drives are set up) and problems with the drive itself. There are occasionally problems with the hard disk controller, but these are less common.





The hard disk won't autodetect at boot time


Explanation: The hard disk is supposed to be dynamically autodetected by the BIOS when the system boots, but the system does not detect it. It either hangs the boot process at the stage where the IDE drive should be autodetected, or it says that there is no disk connected (possibly after a long pause while it searches for the device.)


Diagnosis: One possibility is that the BIOS settings to enable boot-time autodetection are not correct. If the settings are correctly entered, then there is a problem either with the hard disk or with its connection to the hard disk controller or motherboard. (Note that some older drives will not autodetect properly at all, but we're talking very old equipment here.)

Note: SCSI hard disks are detected and set up differently. You will need to consult your SCSI controller documentation for help with problems related to SCSI devices.




There appears to be a failure or problem with a hard disk controller


Explanation: There appears to be a failure of some sort with the hard disk controller. On modern systems the (IDE) hard disk controller is built into the motherboard; on an older system it is typically found as an expansion card. It is easy to tell which type you have by looking to see where the IDE cables go that are connected to the hard disk.


Diagnosis: Actual failures of the hard disk controller are relatively rare; usually the problem is either one of configuration and installation, or is actually the hard disk itself that is causing the problem.





The system hangs up while trying to boot the hard disk when it is first booted after turning it on, but will boot after a warm reset


Explanation: The system will only boot the hard disk after a warm reset is performed when it is powered on for the first time. It will not boot the first time that the power is turned on.


Diagnosis: There are many possible reasons for a hard disk that fails to boot. If a warm reset consistently fixes the problem, however, then this implies that the system is trying to boot the hard disk before it is ready to operate. It takes several seconds for hard disks to come up to speed when they are first turned on, since they must spin up to speed, and then several internal calibrations and tests are often performed. Older BIOSes took thirty seconds or more to complete their power-on tests and boot the operating system, but newer ones can do this in ten seconds or less. Some of these BIOSes are smart enough to wait for the hard disk to signal that it is ready and then will boot, but older ones may hang up.





When I boot up Windows 95, it says it is using compatibility mode for my hard disk


Explanation: Windows 95 is booting up saying that it is using compatibility mode for the hard disk.


Diagnosis: This problem is usually caused by misconfiguration, particularly old drivers that are left over after an upgrade from an older operating system.




I have a SCSI hard disk and IDE/ATA hard disk in the same system, and I want to boot the SCSI one but the IDE one always boots first


Explanation: You have a system with both IDE/ATA and SCSI hard disks installed, but the system insists on booting the IDE hard disk before the SCSI one. Since the SCSI hard disk (usually) has higher performance (often because it uses more advanced technology) it is preferable to boot from the SCSI drive instead of the IDE one.


Diagnosis: Unfortunately, there is no resolution to this problem in many cases. IDE/ATA hard disks are natively supported by the BIOS on most PCs, while SCSI hard disks are not. For this reason, the BIOS is programmed to look first for IDE hard disks and boot them if any are found. The SCSI drives are not looked at until afterward. There are now some newer motherboards (namely the Asus boards) that have a BIOS that will allow you to select booting from SCSI ahead of IDE on a system that has both. Most motherboards do not allow this.





My hard disk has been diagnosed as legitimately being dead (it cannot be accessed at all). Is there anything I can do to recover the data on it?


Explanation: A hard disk that has important data on it has been diagnosed as being dead. The disk cannot be accessed through normal means to recover the data that is on it, but that data must be retrieved.


Diagnosis: Due to the enormous amount of important data that is not backed up regularly and is therefore lost to failed hard disks every year, special companies have sprung up that specialize in performing special heroics on dead drives to access and retrieve data on disks that under normal circumstances would never be readable again. This process is called data recovery. These companies are expensive, and there are sometimes steps you can perform yourself instead of hiring them, although you need to carefully weigh your options before touching your drive and make sure of what you are attempting. These companies are professionals and their success rate is actually pretty high.

Warning: Make absolutely sure that the disk is really dead before you try anything at all in this section. I am assuming that you have diagnosed it properly and also contacted your manufacturer's technical support department. If you aren't sure, don't touch the drive.

Warning: Tinkering with a dead drive can (and often will) void your warranty. If the drive is under warranty, contact the manufacturer's technical support department about data recovery options before you try anything that involves altering the drive. If you alter the drive then the manufacturer may have no choice but to not honor the warranty, since they will have no way of knowing if the problem was indeed caused by your working on the disk.

Recommendation: Assuming that your disk is dead and you want to try "extreme measures" to try to get it running again, try some of the above. Note that if you do manage to get the disk going again, make sure that you will have some other drive set up to pump the data to. You may only get the disk running again once; don't miss the opportunity to save the data:



I bought a hard disk that is supposed to be a certain size (say 4.0 GB), but FDISK or Windows Explorer only reports seeing a smaller number (say 3.8 GB), even though the disk is brand new and empty


Explanation: You bought and installed a hard disk but the system is seeing it as smaller than it actually is supposed to be.


Diagnosis: This is not really a problem at all, but actually a discrepancy in the way drive sizes are reported. Hard disk manufacturers use decimal megabytes (1,000,000 bytes) in their advertising, and BIOS auto-detect routines use the same measure. Other software, especially most disk setup and partitioning utilities like FDIS, use binary megabytes (1,048,576) in their reporting. The difference of about 5% is what you are seeing.





There is hard disk space missing on my disk drive; there should be more space free than there actually is, or the system says the hard disk is full even though there should be space free


Explanation: You are noticing that while your hard disk is supposed to be able to hold a certain amount of data, say 2 GB, that it becomes full despite having several hundred megabytes of less data stored on it. You may also notice for example that you have a volume with 100 MB of free space but you are unable to copy 90 MB of files to it before the disk becomes full.


Diagnosis: It is very common to encounter this, especially on larger disks. In most cases there is really nothing wrong, except that a substantial portion of the storage area of the disk is wasted. In addition, various software packages can consume large amounts of hidden storage. File system corruption can legitimately lead to lost storage space.


Recommendation: "Missing" free space on a hard disk is often caused by a combination of different causes. Try all of the following, since you may find that more than one applies:



I copied the data from a smaller hard disk volume to a larger one and now it takes up more space


Explanation: You put a new hard disk in your system and transferred the information from your older, smaller hard disk to the new one, only to find that the same files are taking up significantly more room.


Diagnosis: The usual cause of this problem is that the larger disk is using a larger cluster size. Under the FAT file system only whole clusters can be assigned to a file, so the larger the cluster size, the more space that is wasted; this is called slack. If you have 3,000 files taking up 300 MB of space on a 340 MB hard disk, then on average, 12 MB of that is wasted space due to the cluster size. Transferring that same data to a new 1 GB hard disk (partitioned in a single volume) will cause the same files to take up about 312 MB of space because the cluster size on the new disk will be 16 KB instead of 8KB.





I have a hard disk that is over 540 MB in size but the system is seeing it only as a 504 MB or 528 MB drive


Explanation: The system is not seeing the full size of your hard disk. In particular, the system is detecting the disk as being either 504 or 528 megabytes (depending on what piece of software is reporting the size). Other than this, the hard disk does appear to work.


Diagnosis: The maximum size of an IDE/ATA hard disk running in standard, untranslated mode is 504 binary megabytes, or 528 decimal megabytes. This is the classic barrier that limits the use of larger hard disks on older systems. In order to use a disk over 504 MB in size, you must have a motherboard or hard disk controller capable of BIOS translation, or you must use a dynamic drive overlay to do the translation in software. If your large disk is showing up as 504/528 MB, then this means that either your motherboard and BIOS do not have translation support, or that support has not been enabled.





I have a disk over 2.1 GB in a system that has BIOS translation, that FDISK or other utilities see as either only 2.1 GB or as a much smaller disk, say only around 400 MB in size


Explanation: There is a hard disk over 2.1 GB in size being used in a system that supports BIOS translation. The disk's size is being presented as either truncated to only 2.1 GB, or it is showing up as a much smaller number like 400 MB for a 2.5 GB drive.


Diagnosis: The most likely cause of this problem is that while your BIOS supports translation, it is not correctly handling disks that have over 4,096 cylinders. There were some BIOSes that did not handle these larger disks correctly; this is one of the hard disk size barriers. Different BIOSes handle these larger disks differently when they aren't supported properly. Some simply truncate the disk to 4,096 cylinders so that the disk appears to be 2.1 GB in size, and others "wrap around" so that they show up as 400 MB (2.5 GB minus 2.1 GB). This is discussed here.

Tip: If this disk is showing up as 504 MB or 528 MB, this is a sign that BIOS translation is not functioning on the machine. Continue here.





I am trying to get two hard disks to work as master and slave on the same IDE channel, but they don't work together properly the way I want them to


Explanation: You are trying to configure two hard disks on the same IDE channel, with one as master and one as slave, but they are not working together properly. Generally, the system will not boot when they are both in the system, or only one of the drives is recognized by the BIOS. Each of the drives will work individually on the channel. You may find that drive A works as master to drive B as a slave, but drive A can't be a slave to drive B as the master.


Diagnosis: Problems getting drives to cooperate as master and slave are common when using drives made by different manufacturers if either of the drives was designed and manufactured before around 1994. Before this time there was not a generally agreed-upon set of standards for master and slave drives working together on the same channel, and problems were common. With two newer drives, problems with putting them on the same channel points more likely to configuration problems. Problems with two drives from the same manufacturer likewise implicates the drives or their configuration, since the manufacturers weren't generally stupid enough to make their own drives not work together.





I need to set up an IDE/ATA hard disk on my PC, but my BIOS doesn't have autodetection capability and I don't know what the disk geometry is


Explanation: You are trying to configure a new (or old!) hard disk on your system. You don't know what the drive geometry is, and your BIOS is old and doesn't provide autodetection capabilities.


Diagnosis: Usually you can find the information you are looking for (cylinders, heads, sectors) by looking on the web page of the manufacturer of the drive.





I want to partition my large hard disk as a single partition but the system won't let me


Explanation: You have a large hard disk, over 2 GB typically, and want to set it up as a single partition, but the system is restricting you to 2 GB maximum (or less).


Diagnosis: The normal limit on partition size in DOS, Windows 3.x and Windows 95 is 2 binary gigabytes, which is about 2.15 decimal gigabytes; this is a limitation of the conventional FAT16 file system. You can use all of a disk that is larger than this (assuming your BIOS will support the disk or you use another way of overcoming the 504 MB disk size barrier) but you must make each partition no larger than 2 GB. The only way around this is using the FAT32 file system available as part of Windows 95 OEM SR2.





don't need the secondary IDE controller on my motherboard and want to disable it so I can free up the resources (IRQ line, etc.) that it is using. I disable it in the BIOS setup but Windows keeps redetecting and installing drivers for it


Explanation: You have a modern motherboard that contains a primary and secondary IDE controller. You want to disable the secondary controller and do so by changing the BIOS setting that controls it. However, Windows 95 keeps redetecting and re-enabling the secondary IDE controller despite its being disabled.


Diagnosis: This problem is caused by the drivers that Windows 95 uses to support PCI controllers. You may have to manually remove the driver for the secondary controller under Windows 95. In some cases you won't be allowed to remove the secondary controller driver because it will say that the secondary controller is "part of a multifunction device" driver that contains the primary and secondary controller drivers. You must change a setting on this "parent" device to disable the secondary controller. If you just remove the parent device then Windows will redetect both primary and secondary controllers again.

Note: If you have any other IDE controllers in the system, such as one that is part of a sound card, it will also show up, usually as "Standard IDE/ESDI Hard Disk Controller". Just ignore it.





I have a dynamic disk overlay installed and usually can see my entire disk but sometimes when I boot I can't access my hard disk, or I can only see 504 MB (or 528 decimal MB) of it


Explanation: A dynamic disk overlay has been installed to permit access to a large hard disk volume on a PC without BIOS support for large disks. The disk normally works fine, but under certain circumstances the disk cannot be accessed, or appears to the system as being only 504 MB in size (528 decimal megabytes).


Diagnosis: A dynamic disk overlay is a driver that is loaded very early in the boot process. This piece of software acts as the translation facility for a BIOS that doesn't have one built-in, allowing access to a large hard disk on a system that would otherwise be limited to 504 MB per disk. If anything happens to cause the overlay not to be loaded during the boot process, problems will result. Common culprits are booting from a floppy disk that wasn't made using the dynamic drive overlay software and also viruses.



Note: If you need to boot the system clean to get rid of a virus, booting the hard disk first in this manner will be self-defeating, but booting a regular floppy disk straight will not allow proper access to the hard disk. This is why you need a boot floppy that includes your drive overlay



I am having problems or getting errors with my dynamic disk overlay program


Explanation: There is a problem with the dynamic disk overlay software being used to allow access to the full contents of a larger hard disk on an older PC.


Diagnosis: Dynamic disk overlays are really kludges, pieces of software that are trying to act as mediator between a disk drive and a BIOS that can't properly support it. They work fine in most cases but there can be many different reasons why they have problems under various circumstances.





I booted from the floppy disk and I can't see my compressed disks


Explanation: The compressed disk volumes on the system cannot be seen after booting the PC from a floppy disk.


Diagnosis: Compressed disks require a driver in order for them to be properly accessed. If you are booting a disk that does not contain the correct compression driver, or if you are booting from an older version of DOS, you will not be able to see your compressed volumes because the correct driver software is not being loaded.





I've compressed a disk volume and now I've noticed that disk access (and/or the system as a whole) seems slower


Explanation: Disk compression was installed on the system and a compressed volume created. Using this volume now seems slower than it was before.


Diagnosis: This is a common side effect of using compression and is generally more often the rule than the exception. Compression works by adding a software interpretation layer and this takes processing time compared to just writing the data directly. The slowdown is especially noticeable on PCs with slower processors. On faster processors, compression can in theory improve overall performance by reducing the number of accesses to the (slow) hard disk. Compression performance is discussed in detail in this section of the Reference Guide.





I am encountering compression errors on my compressed volumes


Explanation: While checking the file system or while performing work using the compression utility, compression errors were discovered in one or more compressed volumes.


Diagnosis: Compression errors are usually either a flaw or incompatibility with the compression software, or a more generalized problem with the hard disk itself.





The system is telling me I am out of space on my compressed disk even though I should still have space left


Explanation: The system said I had a certain amount of space free on my compressed volume but when I tried to copy an amount of files that should have fit, the disk ran out of space before copying all the files.


Diagnosis: It is impossible to know exactly how much free space there is on a compressed volume. The reason is that the amount you can store on the volume depends on how much its contents can be compressed, but the system doesn't know what the right ratio is until after the files have been copied. Therefore, the compression driver only estimates the amount of free space on the drive. If you copy a bunch of files to the volume that don't compress very much, you will use up a disproportionate amount of the free space. This is discussed in much more detail here, including an example.






When I added a new disk drive, the drive letters assigned to my original hard disk's volumes changed


Explanation: After adding a new hard disk drive, the letters that were previously assigned to partitions on the old hard disk changed.


Diagnosis: This is a residue of the way DOS assigns drive letters. As discussed in detail here, DOS (and Windows) assigns drive letters first to the primary partitions in all hard disks in the system, and then to the logical partitions after that. If you start with a disk containing a C: primary partition and a D: logical disk volume, adding a new hard disk with a primary partition will cause the logical on the first disk to be pushed to E:


Recommendation: When adding a second hard disk to an existing system, partition it so that it contains only logical drives. Do not create a primary partition at all. This will cause the drive letter order to be preserved



One of my disk volume drive letters isn't accessible any more or isn't visible in Windows Explorer


Explanation: A drive volume letter appears to be "missing" from the system. For example, there may be a C:, D: and E: drive but only C: and D: show up in Windows Explorer.


Diagnosis: Assuming that there isn't a fault with the hard disk itself, the problem here is likely that the drive letter has been hidden by the operating system for one reason or another.





I booted from my floppy disk and now I can't see one or more hard disk volumes that work when I boot from the hard disk itself


Explanation: After booting from a floppy disk, one or more of the hard disk volumes that are normally present on the system seems to disappear.


Diagnosis: This is usually caused by drivers that are on the hard disk being bypassed when the floppy disk is booted. Another culprit is the ever-present virus threat. Some particularly nasty viruses encrypt the hard disk structures; when the hard disk is booted they load and then "decrypt" the structures on the fly. When you boot from the floppy the virus is bypassed and the encrypted structures cannot be read by the system. (Obnoxious, isn't it?)





My hard disk has bad sectors or is developing bad sectors over time


Explanation: The hard disk (through disk checking utilities) is reporting that one or more of its sectors are bad. This may be on a new drive, or there may be bad sectors showing up on a drive that has been in a system for a while.


Diagnosis: Unsurprisingly, bad sectors are generally a real problem with a hard disk and usually imply a legitimate problem with the hard disk itself. There are configuration problems that may be responsible, and these are usually resolved pretty easily, however the usual problem is the drive itself. Bear in mind that IDE/ATA and SCSI drives, at least all of the ones produced in the last five years or so, use a technique called remapping or spare sectoring to hide bad sectors detected on the drive at the factory. A new hard disk should have zero bad sectors on it. An older drive may "grow" a bad sector or two now and again, however in many cases this is a harbinger of impending disaster with the disk. Take it as the warning sign it is.


Recommendation: The steps below discuss possible problems that can lead to a bad sector showing up. In addition to trying to eliminate the cause, you also should contact your hard disk manufacturer's technical support department (phone or web site) and inquire about a utility to remap the bad sector so it is hidden and replaced with one of the spares on the disk (fixing the cause of the bad sectors is important but that doesn't get rid of the ones that are already there in some cases):



Serious disk errors are occuring trying to read or write a disk volume (sector not found, general failure, etc.)


Explanation: The system detected an error trying to access a disk volume. The drive letter is specified in the error message and could be a hard disk, floppy disk, mapped network volume, etc.


Diagnosis: This sort of message on a hard disk can mean either file system corruption or bad sectors on the drive. It can also be caused by software or driver bugs, or by running out of system resources under Windows 3.x.





Not ready reading drive X:


Explanation: You attempted to read from a disk volume that wasn't ready to send data to the system.


Diagnosis: This is almost always caused by trying to read data from a removable storage device that has no media in it, such as an empty CD-ROM drive or floppy disk drive. If it occurs with a hard disk, this probably means the drive has a problem or is misconfigured.





I get a "Runtime error" running FDISK on my Western Digital hard disk


Explanation: While attempting to access a Western Digital hard disk using FDISK, a "Runtime error" is encountered.


Diagnosis: This error message means that there has been some corruption or damage to track zero (where key file system structures are stored).




The hard disk is very hot while in operation


Explanation: The hard disk feels very hot while it is operating.


Diagnosis: It is normal for hard disks, especially newer ones, to feel hot while they are operating. They should not get as hot as solid-state components like processors; they will often feel warm to the touch but should not be uncomfortable to put a hand onto. Newer disks that spin at 7200 RPM or higher will tend to get hotter than older, slower drives. A properly-ventilated case should be able to handle all but the hottest drives without additional cooling measures being required.





The hard disk is vibrating a great deal while running


Explanation: The hard disk is causing a great deal of vibration as it spins while running.


Diagnosis: Hard disks, especially newer ones, do vibrate to some extent, although this should not be excessive. Better quality disks will normally have less vibration than cheaper ones. A disk that vibrates a great deal or that starts vibrating more than it did in the past may be headed for failure. On the other hand, some vibration is not a great concern.





The hard disk activity LED flickers every few seconds even when nothing is running on the PC and it is completely idle


Explanation: The activity LED on the system case flickers every few seconds, even when nothing is going on with the PC.


Diagnosis: There are a couple of possible explanations for this behavior. First is Windows 95's "auto-insert notification". The feature that automatically loads software from CD-ROM drives works by constantly checking to see if there is a CD-ROM disk in the drive. This causes the activity light to flicker on some systems. Another possibility is that there is system work occurring that you may not be aware of. Windows does do some housekeeping work at occasionally odd times, and there can also be background tasks that run from time to time.




The hard disk heads can be heard moving occasionally even though the system is idle and the activity LED is off


Explanation: You can hear the hard disk head moving or other sounds of activity, but the system is idle and the hard disk activity LED does not light up.


Diagnosis: The most usual cause of this observed behavior is internal thermal recalibration being performed by the hard disk. This procedure is performed by many types of hard disks as they warm up, to ensure that they compensate for thermal expansion of the platters. Another feature that can cause this is the "wear leveling" feature now being used by Western Digital and possibly some other manufacturers, which causes the disk to move from track to track every 15 seconds when idle. If you see disk activity while the system is idle that includes the hard disk LED being lit,



My hard disk spins down after a period of inactivity even though I disabled power management in the BIOS


Explanation: You have turned off power management, but the hard disk still spins down after a period of inactivity.


Diagnosis: Sometimes the power management isn't really turned off; it's possible that more than one BIOS setting needs to be changed and they weren't all changed. There could be a BIOS bug as well.





I hear a clicking or clunking sound coming from the hard disk occasionally


Explanation: Every once in a while the drive makes a "click-click-click" or a clunking noise, either while it is operating or sitting idle.


Diagnosis: This is usually a message, and the message is: "look out!" Generally speaking, hard disks should not make these sorts of noises. Do not confuse a loud clicking or thunking sound with the quiet "tapping" access sound made by some drives performing thermal recalibration. Also, some newer drives (such as those made by Western Digital) use a feature called "wear leveling", that causes the disk to move from track to track every 15 seconds or so to prevent the heads from sitting over one area of the disk for an excessive period of time (which could increase the possibility of a wearout failure). Time the interval between clicks; if it is 15 seconds exactly and the drive is otherwise fine, this is likely what is going on, and you probably do not have to do anything.





I hear a loud buzzing sound or rattling sound coming from the drive


Explanation: The hard disk is making a buzzing or rattling noise and/or is vibrating a great deal when in operation.


Diagnosis: The most common cause of this problem is that the bearings in the drive are causing trouble. This is a relatively common problem. Noisy bearings don't affect the performance of the drive (other than aesthetically), but problems of this sort have a tendency to get worse over time. On a newer drive this is often the sign of a manufacturing defect.






I am experiencing file system corruption problems, such as lost clusters, cross-linked files or invalid files or directories


Explanation: While performing routine file system scans, errors are being detected on one or more disk volumes. These errors are usually lost clusters or cross-linked files. Compression errors on compressed volumes are discussed here. The disk itself otherwise works OK although a handful of files might be corrupted; if the disk is corrupted to the point of unusability, or if its contents appear scrambled, look here instead.


Diagnosis: A small number of file system problems is normal on just about every PC, depending on what kind of operating system and software you are using. In particular, lost clusters are common because any time an application crashes or there is a power outage, in fact any time an application is interrupted, it may leave behind partial files that show up as lost clusters because the file was never completed properly. However, finding large quantities of lost clusters even when scanning regularly, or repeatedly finding problems like cross-linked files or invalid files or directories, can be a signal of a more serious problem.

Note: A lost cluster is not the same thing at all as a bad sector (which is a physical disk problem, not a file system problem); see here for more on those.


Recommendation: You may want to try all of the following items:



I have files or directories disappearing from my hard disk volume


Explanation: One or more files or directories seem to have "disappeared" from a disk volume. You were using them or referenced them recently, but now they are nowhere to be found.


Diagnosis: Files that seem to be lost on a hard disk are more often simply "misplaced" than actually lost. By this I mean that the files have been moved by the user, or the wrong file name or directory name is being used, so the file is still there but seems to be gone. Rarely, a disk corruption problem or virus can really make a file disappear.





The hard disk's file structures have become corrupted or the data on it is unreadable (an existing disk volume is acting as if it is unformatted, or there are very serious disk errors)


Explanation: The hard disk is generating error messages or is otherwise behaving as if it has become seriously corrupted. An existing, working hard disk may be acting as if it had been wiped clean, or had been never formatted. Strange error messages or very large quantities of files may be corrupted or wiped out. Note that small numbers of lost clusters or other minor file system corruption are often a result of more benign situations and are discussed here instead. (Bear in mind that if you don't scan for file systems regularly, they can accumulate and make the situation look a lot more dire than it really would be if the disk had been maintained properly.)


Diagnosis: There are a myriad of possible causes for a hard disk that is experiencing a large amount of corruption; most of them are, unfortunately, pretty serious. In many cases it is not the hard disk itself but rather an external factor that is causing the problem.





I think I have a virus on my system, what should I do?


Explanation: You suspect, for whatever reason, a virus infection on your hard disk and are not sure what to do about it.


Diagnosis: Viruses are commonly responsible for a number of system problems that are blamed on hardware failures or software bugs. It makes sense to eliminate them as a possible problem source before ripping the machine open. Checking for viruses is normally as simple as installing a virus scanner and running it.


Recommendation: You will want to do all of the following:



I accidentally deleted a file, can I get it back?


Explanation: You have accidentally deleted one or more files and wish to undo the deletion and recover the file.


Diagnosis: On a modern system undeleting files is relatively simple, as long as you realize relatively quickly that you want to restore the file. Regular deletion of a file doesn't actually erase the contents of the file; it simply marks the file as deleted in the directory. The file's contents remain where they were, though they are made available for other files to use. As long as you remember to try to undelete the file soon, you should be able to recover it. In addition, many operating systems and utility programs store recently-deleted files intact in case they are needed. In Windows 95, for example, this is the "Recycle Bin".


Recommendation: As soon as you realize that you want to undelete a file that you recently deleted, avoid doing anything more on the system that involves the hard disk. Every time you create or change a file, you increase the chance that the contents of the file you want to recover will be overwritten with something new, unless it is in a protected area like the Recycle Bin:



I accidentally formatted a disk volume, can I still get the information that was on it back?


Explanation: A hard disk volume has been accidentally formatted, and it is desired to get the information on the disk back again.


Diagnosis: Performing a high-level format on a hard disk doesn't really "format" it the way a low-level format does; it just writes the file system structures. As a result, reformatting a drive just wipes out the existing structures (the root directory entries, etc.). The data itself is still on the drive, unless you specifically used a special application that wipes all the data in the files as well (these programs are used sometimes for security reasons). There are unformatting utilities that will reverse the formatting process, perhaps only partially depending on the circumstances.





I am running Windows 95 and using long file names, but they sometimes seem to get lost or deleted somehow


Explanation: You are using long file names in Windows 95 (file names that are longer than the standard DOS 8.3 convention) but sometimes the file's longer name disappears. For example, a file named "March Results.doc" may at some point end up having only the name "MARCHR~1.DOC". You may find that only the short file name alias shows up when you copy the file to another machine or to a floppy disk.


Diagnosis: Long file names are a welcome addition in Windows 95, but to be blunt, their implementation was a hack. In order to maintain compatibility many compromises were made in the way that they work, and several different things can cause them to become lost from the file system.


Recommendation: The problem could be caused by any combination of the following:



I've benchmarked my hard disk (or evaluated it subjectively) and it seems to be getting slower over time


Explanation: You benchmarked your hard disk's performance when it was relatively new and then again recently, and noticed that the scores are going down; or, you've just noticed yourself that the disk seems to perform more slowly than it once did.


Diagnosis: This is fairly normal and is not usually indicative of a problem situation. There are several reasons why performance will tend to decrease over time. First is that when a hard disk is first used, it fills up from the outside of the disk in towards the middle. The outer part of the disk has the fastest transfer rate because of how data is recorded on the disk using zoned bit recording. Second is the tendency for files and directories to become fragmented, which hurts performance; regular defragmentation can help with this. Third, most people (if you are anything like me) enjoy collecting "neat" utilities, software enhancements, hardware drivers (for new gadgets) and install all this stuff on their machine. This will tend to slow the machine down by taking CPU cycles and also by using up memory, which can affect benchmarks and also make the PC seem generally sluggish. Finally, the system as a whole will slow down if the disk gets too full. Running with your disks more than 90% full is not ideal.


Recommendation: There isn't much you can do to prevent slowdown of this sort from happening, but there are some specific steps you can take to improve performance of your hard disk if this is an important issue to you. Also check out these tips in the System Optimization Guide:


I installed PCI IDE bus mastering and I notice little or no speed improvement (or performance decreased)


Explanation: In an attempt to improve performance on your system under Windows 95, you have installed bus mastering drivers. While the drivers work, there is no great performance improvement, as you may have been expecting.


Diagnosis: Join the club. As I've said elsewhere on this site, I find all the hoo-hah about bus mastering drivers totally amazing. Why they are so hyped up, considering that they have so many compatibility and installation problems and they provide so little real benefit for the average person, is totally beyond me. Oh well.





I added a new, modern hard disk to my older system, but it is performing slower than it should


Explanation: You upgraded or replaced your hard disk, but it is still performing at a speed comparable to your older drive. The transfer rate performance is not quite as good as you were expecting, or benchmarks are lower than what others are getting for the drive.


Diagnosis: As discussed in detail in this Reference Guide section on hard disk performance, the performance level of a hard disk is dependent on many different factors. Some of these are a function of the hard disk itself, but many are a function of the other parts of the system. Most hard disk benchmarks in fact are influenced by the speed of the chipset, processor, memory and other components. Also, putting a new hard disk into an old motherboard can greatly limit its performance because the interface may not be capable of running at the higher modes that are required for peak performance. Remember to check out this section in the Optimization Guide on hard disk performance.





I am running Windows 95 OEM SR2 but my hard disk isn't using FAT32. Isn't FAT32 part of Windows 95 OEM SR2?


Explanation: Windows 95 OEM SR2 is installed, which allows the use of FAT32 partitions, but after installing it, the system still appears to be using the older FAT (FAT16) disk volumes.


Diagnosis: FAT32 is a disk format, and while support for it is part of Windows 95 OEM SR2, this does not mean your disk volumes automatically are always going to be FAT32 just because you are running OSR2. You must use the correct tools and create FAT32 volumes if you want to use them, or convert your existing FAT16 volumes to FAT32.





I am having problems with the system after installing PCI IDE bus mastering drivers


Explanation: In an attempt to improve performance on your system under Windows 95, you have installed PCI bus mastering IDE drivers. After installation, problems are being exhibited ranging from hard disks not working correctly or being recognized, CD-ROM drives not working, general system instability, or other issues.


Diagnosis: In my opinion, setting up bus mastering IDE under Windows 95 has the lowest value (measured as the ratio of true performance improvement to implementation hassle and cost) of just about anything you can do to optimize your machine. There are so many different problems that they cause, and so many pieces of hardware and software they don't work with, that I no longer bother with them due to the minuscule improvements I see when using them. In short, if the problem appears after installing these drivers, I generally recommend uninstalling and forgetting about them. Below I list some specific gotchas and incompatibilites to watch out for. When you see how long it is (and I am sure that it is not comprehensive) you will know why I don't bother with these drivers any more.


Recommendation: First of all, read this section in the Reference Guide that discusses the requirements for running PCI IDE bus mastering. Then also read this section on IDE bus mastering in general. Then, consult the list below for possible specific causes of your problems; you may find something here that will help you fix the trouble, but it is just as likely that you will simply find confirmation that they just are not going to work with your PC:



I installed PCI IDE bus mastering and I notice little or no speed improvement (or performance decreased)


Explanation: In an attempt to improve performance on your system under Windows 95, you have installed bus mastering drivers. While the drivers work, there is no great performance improvement, as you may have been expecting.


Diagnosis: Join the club. As I've said elsewhere on this site, I find all the hoo-hah about bus mastering drivers totally amazing. Why they are so hyped up, considering that they have so many compatibility and installation problems and they provide so little real benefit for the average person, is totally beyond me. Oh well.





I want to enable 32-bit disk access under Windows 3.x but it does not work on my system


Explanation: There is an option in Windows 3.x to enable so-called "32-bit disk access" but whenever you enable it, an error message is generated saying that a problem occurred and you have to turn it off.


Diagnosis: First of all, this feature was totally misnamed by Microsoft. There is no such thing as "32-bit access" to an IDE hard disk, because the IDE/ATA interface is 16 bits wide. The 32 bits being talked about here really refer to the use of 32-bit protected-mode software to access the hard disk. In essence, its simply about using better drivers to access the disk instead of using the native BIOS disk routines. The problem is that Windows 3.x ships only with an ancient generic driver that is five years old and does not handle modern hard disks properly. Unless you are using an older hard disk, you need a specific driver to handle your disk to enable this feature.





There is frequent access to the hard disk when working within Windows, even without actually performing file operations. For example, frequent disk access when swapping between open applications


Explanation: The system seems to be going to the hard disk a lot, even when you are working only with items that are already in memory. For example, when scrolling up and down in a large file, there may be a pause while the hard disk is activated. You may especially notice it when swapping between applications.


Diagnosis: The most usual cause of this sort of behavior is what is called thrashing. This refers to the excessive use of virtual memory paging to compensate for having insufficient real physical memory to hold all of the applications and data that are in use. Especially if you are using many applications or large files, and also if there isn't a great deal of real memory in the PC, the operating system will have to move some of the contents of memory to the hard disk when it runs out of space. Then, when you need whatever was swapped to disk, it is loaded and something else is swapped to the disk. This is a supply and demand situation; the only way to resolve it is to increase the supply of real memory, or reduce the demand created by applications and data open simultaneously.