Hardware Reference
In-Depth Information
simply start over by removing and re-creating all the partitions (which will lose any and
all data they contain), or investigate data recovery options if you don't have backups and
need the data back.
Error Loading Operating System
Once the MBR code makes it past the Boot Indicator byte check, and one of the partitions
is marked active (bootable), the MBR code continues by looking at the rest of the in-
formation in the active partition table entry to determine the starting sector location for
the active partition. The starting sector location is a sector address indicated by both CHS
(cylinder/head/sector) andLBA (logical block address) values. The CHS value isusedfor
drives 8.4GB or smaller in capacity, whereas the LBA value is used for drives larger than
8.4GB (pretty much all drives today). The first sector of a partition contains the volume
boot record (VBR), which is also known as the operating system boot record because it
is installed on the drive during the OS partition format process. Once the VBR address of
the active partition has been determined, the MBR code reads that sector from the drive.
If the VBR of the active partition can't be read successfully due to a read error (physical
problem with the disk), a series of five retries occurs. If after all the retries the VBR still
cannot be read, the following message is displayed and the system stops:
Error loading operating system
This is a bad message to see because it generally indicates physical problems with the
drive. However, this message can also appear if the drive parameters are incorrectly
entered in the BIOS Setup, or if the VBR sector location as listed in the MBR partition
table is invalid. Forexample, if the MBR contains an invalid VBR address that points to a
sector beyond the physical end of the drive, this message results.
If you see this message unexpectedly, first check the BIOS Setup settings for the drive to
be sure they are correct, then check the partition table entries, and finally run a diagnostic
test of the drive itself. If the drive is bad or going bad and you need the data back, you
may require the services of a professional data-recovery outfit.
Missing Operating System
If the MBR code has successfully loaded the VBR with no read errors, the MBR code
checks the last two bytes of the VBR for the 55AAh signature. If the signature is not
present, the MBR displays the following error message and halts the system:
Missing operating system
This would be an expected occurrence if, for example, you had just created the partition
and had not yet done a high-level format, meaning that the partition has not yet been
formatted by the OS, or no OS is yet installed.
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