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| Troubleshooting Hard Disk Drives | Dynamic
Drive Overlay Problems ]
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.
Recommendation:
- Scan the system for viruses to make sure that
it is clean.
- Beware of booting the system from boot floppies unless they have been specially prepared
using your dynamic drive overlay software, which should be able to create boot disks that contain the overlay to allow you
to boot from a floppy disk and still access your hard disk. It is recommended that you
have at least two of these boot floppies created by the dynamic drive overlay software.
- If you want to boot a regular bootable floppy, you should start the system with the
floppy released from the floppy disk and boot the hard disk first. The overlay will print
a message telling you to press a key (such as the space bar) if you want to boot from the
floppy disk. Then insert the floppy and boot it.
 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.
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