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The following article is the second in a series that helps solve many 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 computer service department. This article is designed to work with a system that has a single drive using a FAT 16 structure (all DOS and older Windows systems, some Windows 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 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.
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