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It is extremely important not to make or write any changes to data on the hard drive without first verifying the hard drive configuration. Therefore, the first priority when unable to access information on a hard drive is to verify all of the configuration information dealing with the suspect hard drive.

Partition Parameter

Value or Equation

Partition Status

Bootable

Starting Head

1

Starting Sector

1

Starting Cylinder

0

Partition Type

Bigdos (drives greater than 30 MB), otherwise DOS 12

Ending Head

Total Number of Heads -1

Ending Sector

Sectors per Track displayed in Volume Boot Sector

Ending Cylinder

Number of Cylinders set in CMOS - 2

Total # of Sectors

Number of Sectors displayed in Volume Boot Sector

Start Absolute Sector

Number of Sectors per Track in Volume Boot Sector

Boot Signature

55AA

Step One: Make sure that Micro-Scope detects the hard drive

In Micro-Scope, System Configuration, Compare Settings - check to make sure that there is not an asterisk beside the number of hard drives detected value. If there is an asterisk, either the CMOS is set incorrectly, or there is an electronic problem (controller, cable, drive).

Step Two: Compare the BIOS parameters against the drive partition information.

In Micro-Scope, System Configuration, System Information - note the information displayed for the hard drive, specifically the parameters for the drive in question. Compare these parameters to the parameters in the MBR display under Micro-Scope, System Configuration, Partition Display using the following formula:

System Information

Master Boot Record

Cylinders

Ending Cylinder + 2

Heads

Ending Head + 1

Sectors

Sectors Per Track

If the information does not match, either the partition information is corrupt, or the CMOS setup or controller BIOS setup (if one exists) is incorrect, or there is a problem communicating with the drive.

Step Three: Check the drive functionality

In Micro-Scope, Diagnostics, Fixed Disk Tests - check the information in the Fixed Disk Selected window. Make sure that the proper drive type, model, and native parameters are showing in this window. If any of the information is incorrect, there is an electronic problem. Check the cable, controller and drive, re-seating all connections, and repeat the above procedure. After correcting the electronic problem, perform a read test on the first 10 cylinders of the drive. If any errors occur, then this is the most likely cause of the drive failure. Perform a read of the entire drive to determine if the errors are electronic in nature, or physical in nature. Electronic problems will result in the errors displayed not always being the same type or in the same location on the drive. If the problem is electronic, replace the cable, controller, and finally drive electronics and repeat the read test until no errors occur. If the error is physical, use an INT 13 type editor (such as Norton Advanced Editor), to block the entire drive and write the information to a daisy chained drive set to the same parameters as the faulty drive.

The next step, after the drive passes the read test on the first 10 cylinders, is to check the original partition setup of the drive.

Step Four: Check for the physical location of the master boot sector and the volume boot sector.

In Micro-Scope, Utilities, Fixed Disk Editor - use the FIND feature to search the last two bytes of each cylinder for a boot signature (55 AA). The first location where a boot signature should be found would be at cylinder 0, head 0, sector 1 (the master boot sector). The second location where a boot signature should be found is at cylinder 0, head 1, sector 1 (the volume boot sector). It is also possible to use the FIND feature to locate the volume boot sector by searching for MSDOS (in DOS based systems) or MSWIN (in Windows95 systems).

If there is a duplicate copy of the master boot sector found before the location of the volume boot sector, then it is possible that a boot virus has infected the hard drive in the system. The Rebuild Master Boot feature of Micro-Scope will eliminate any boot sector virus. Be sure to boot the system to the Micro-Scope diskette and immediately do a cold reboot of the system after using the Rebuild Master Boot feature.

If the volume boot sector is found in a location other than cylinder 0, head 1, sector 1, count the actual number of sectors before the volume boot sector, and compare that value to the value for the sectors per track displayed in the partition table described in step 2. If the values match, the most likely cause of the system failure is an incorrect CMOS setup. In this case the CMOS needs to be reset to the values indicated by the partition table described in step 2, remembering to use the formula described in step 2 when doing so. If the values do not match, set the CMOS Sectors Per track to the number of sectors counted before the volume boot sector and continue to the next step.

Step Five: Check the partition tables to make sure they are correct

Reboot the system to Micro-Scope and go to System Configuration, Partition Tables. Check the information displayed in the master boot record to see if there is any obvious corruption (that is, excessively large numbers, all partitions non-bootable, etc.) If there is no obvious corruption in the master boot record, then perform step 2 again. If the information matches at this point, go to step 6. If the information does not match, then set the sectors per track in the Master Boot Record to the number of sectors per track currently set in CMOS, set the starting head to 1, starting sector to 1, and starting cylinder to 0, and write the information to the drive.

Step Six: Verify the Master Boot Sector information

Display the Volume Boot Sector and use the values for heads and sectors per track (on the right half of the screen) to perform step 2 again.

If the values match, then the volume boot sector is probably okay. If any values in the Master Boot Record do not match the table to the right, reset the values to match the values in the table, and write to the drive.

If the values still do not match, both the Master Boot Record and the Volume Boot Record are probably corrupt. At this point, e-mail Technical Support for help in this situation. Future articles will provide more insight into the repair procedure.

Step Seven: Check the FATs

Check to see if the first FAT starts on the sector just beyond the volume boot sector. Use the find feature in the Fixed Disk Editor to search for F8 FF FF in the first three bytes of each sector. The first occurrence should be on sector two of head one. Continue to search until the second FAT is found, indicated by the second occurrence of F8 FF FF. Note the location of the cylinder, head and sector of the second FAT.

Based on the start of the second FAT, and the start of the first FAT, calculate how many sectors are in the first FAT. If necessary, read each sector starting at the first sector of the first FAT, keeping a count of the sectors that have been read until F8 FF FF is seen in the upper left of the HEX display, which would indicate the start of the second FAT. After calculating the sectors per FAT, compare this value to the value in the volume boot sector. If the values match, the drive should be accessible through DOS at this point.

Step Eight: Attempt to access the drive

Boot to a DOS-bootable floppy diskette and attempt to access the drive. If the root directory and sub-directories on the hard drive are readable at this point, then attempt to boot to the drive. If the drive boots at this point, the problem has been corrected. If the drive is still not bootable, e-mail the Micro 2000 Technical Support department for help.

Disclaimer - The Micro 2000 Tech Tip is a free service providing information only. While we use reasonable care to see that this information is correct, we do not guarantee it for accuracy, completeness or fitness for a particular purpose. Micro 2000, Inc. shall not be liable for damages of any kind in connection with the use or misuse of this information.

Micro 2000 Inc has been helping to solve the day-to-day challenges that IT departments face in order to keep their businesses operational as well as profitable for over 14 years. The company’s primary goal is to put the customer first - through feature-rich, simple-to-use IT tools that can help IT administrators manage their jobs more effectively.

For more advice and free articles be sure to visit: http://www.micro2000.co.uk

Tags: computer, diagnostics, hard drives, maintaining pcs and computers, PC, pc and computer tools, tech tipscomputer, diagnostics, hard drives, maintaining pcs and computers, PC, pc and computer tools, tech tips

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A common problem with hard drives is the error message “MISSING OPERATING SYSTEM.”

Typically what this means is that critical data is missing or damaged in two possible locations. The first is the Master Boot Record (MBR). This data area contains error messages and pointer information that specifies the location of the second critical data area, the Volume Boot Record (VBR). The VBR contains the operating system specific data for the format of that particular partition on the drive. If either of these two critical data areas is damaged, by a virus, controller failure, etc., then the drive will not be accessible through the operating system.

The normal response to this error message is to boot to a floppy disk and to re-partition the drive (probably using FDISK) and thereby totally removing any possibility for recovery of the data on that drive, except by dedicated data recovery software or a data recovery facility. If applicable, the following technique will help save time, money, and frustration.

The first step to data recovery (covered in great detail in the first article of this series) is to verify the location of the existing partition information. For the purposes of this article, it will be assumed that the FAT structure and the root directory are intact, there is only one partition, and that only the MBR and the VBR were damaged. Using Micro-Scope, enter the Fixed Disk Editor menu and select the fixed disk that is being repaired. Using the Find menu option, locate all the sectors that contain the string “55 AA” (see Step Four of the first article in this series), and then verify that the FAT structures are intact (see Step Seven). Note on a scratch paper the values (in Cylinder, Head, Sector format) where this string appears. These values will be used later in the reconstruction process.

Rebuilding the MBR

Using the Fixed Disk Editor in Micro-Scope, locate and read Cylinder 0, Head 0, Sector 1. This should be the location of the corrupt Master Boot Record. Press “M” to modify the sector and enter 0’s for the entire sector, effectively wiping all the data from this sector. Press ESC, then “W” to write the data, and “Y” to confirm the write operation. Then exit the Fixed Disk Editor and select the Rebuild Master Boot Record menu option. Press “Y” to confirm this operation. The fixed drive now has a completely corruption-free MBR available for use during the reconstruction of the VBR.

Rebuilding the VBR

There is a simple method for rebuilding the VBR. Copy the data from a like fixed disk or a similar-sized fixed disk with the identical operating system (the versions must be the same.) There are two approaches for obtaining this data. The first is to install the second drive in the system, reboot Micro-Scope, and copy the sectors directly from the “healthy” drive to the drive being reconstructed. The second method is to copy the sectors from the “healthy” drive to a floppy diskette and transfer that diskette to the machine containing the drive being reconstructed. The data can be copied to any sector on the floppy disk. Just note where this data is stored on the floppy disk so that it may be easily retrieved when copying it back to the drive being reconstructed. In either case, the VBR is located at Cylinder 0, Head 1, Sector 1 on the “healthy” drive. Copy this data to the same location on the damaged drive. Exit the Fixed Disk Editor.

The drive now has a clean MBR and VBR, and with a few modifications to the values stored in these data areas, the drive will be fully reconstructed.

Access the VBR in the Partition Editor. Some of the values in this area will remain the same. These are: Bytes Per Sector, Reserved Sectors, Number of Copies of FAT, Max # of Root Dir. Entries, Media Description Byte, and Volume Boot Signature. Sectors Per Cluster may or may not need to be changed. Put the cursor over this value and press F1 for a formula that will help determine the proper value. Use this same F1 procedure for determining the Total Number of Sectors. This value should be the same as the value for Number of Sectors in the partition table.

The Sectors per FAT value equals the number of sectors from the beginning of the first FAT to the beginning of the second FAT (as described in the first article in this series.) The values for Sectors per Track and Number of Hidden Sectors should be identical to the values in the MBR. The Number of Heads is either the same as the value in the MBR or the same as the value of the Number of Heads in the partition table plus one (refer to the first article in the series for more information on this topic.) After completing this information, the drive should either be bootable or accessible via a bootable diskette. If this is not the case, e-mail the Technical Support department for further verification of the problem.

Reconstructing Multiple Partition Volumes

In some cases, the drive may have been partitioned into smaller, logical partitions. If this is the case, the chance of this data being corrupt is slim, and correct Head and Sector values are readily available from these areas. To find the second partition on the drive, use the Fixed Disk Editor in Micro-Scope to view the sector containing the “55 AA” string. This sector should appear after the first VBR, so don’t confuse the two. The second MBR should start on Head 0, Sector 1 of a given cylinder. Accordingly, the second VBR will appear on Head 1, Sector 1, and the FAT on Head 1, Sector 2, etc. By adjusting the first MBR in Micro-Scope so that the value for Starting Cylinder, Head and Sector is equal to the location of the second MBR, the VBR is now accessible through the Micro-Scope partition editor. Use these values to reconstruct the second MBR. The only value that will need recalculating is the Start Absolute Sector in the second MBR.

As outlined in the first article in the series, the Start Absolute Sector is the same as the value for Ending Sector. This is not the case with a second partition. The Start Absolute Sector is the number of sectors prior to the VBR. The formula for the Start Absolute Sector is as follows: (Number of Sectors) + (the Start Absolute Sector of the previous partition) + (Sectors per Track). This formula will work for any additional logical partitions.

If, during partition reconstruction, there is something not understood, e-mail the Micro 2000 Tech Support Dept. before making changes to the drive.

Disclaimer - The Micro 2000 Tech Tip is a free service providing information only. While we use reasonable care to see that this information is correct, we do not guarantee it for accuracy, completeness or fitness for a particular purpose. Micro 2000, Inc. shall not be liable for damages of any kind in connection with the use or misuse of this information.

Micro 2000 Inc has been helping to solve the day-to-day challenges that IT departments face in order to keep their businesses operational as well as profitable for over 14 years. The company’s primary goal is to put the customer first - through feature-rich, simple-to-use IT tools that can help IT administrators manage their jobs more effectively.

For more advice and free articles be sure to visit: http://www.micro2000.co.uk

Tags: computer maintenance, computer repair, hard drives, hardware, pc maintenance, pc repair, tech tipscomputer maintenance, computer repair, hard drives, hardware, pc maintenance, pc repair, tech tips

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