The following article is the second in a series that helps solve much of the common boot problems with hard drives.

The article explains how to reconstruct the Volume Boot Record and will touch briefly on multiple-partition drives. This information will help solve some very common problems encountered in a Notebook service dept. This article is designed to work with a system that has a single drive using a FAT 16 structure (all DOS and older win systems, some win NT), and no drive overlay.

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

Typically what this means is that critical dataoperating systemcontroller 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.

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

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 duplicate 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 duplicate. 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 worth. Use this duplicate F1 procedure for determining the Total Number of Sectors. This worth should be the duplicate as the worth for Number of Sectors in the partition table.

Reconstructing Multiple Partition Volumes

As outlined in the first article in the series, the Start Absolute Sector is the duplicate as the worth for Ending Sector. This is not the case with a second partition. The Start Absolute Sector is the number of sectors previously 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.