Learn about the technologies behind the Internet with The TCP/IP Guide!
NOTE: Using robot software to mass-download the site degrades the server and is prohibited. See here for more.
Find The PC Guide helpful? Please consider a donation to The PC Guide Tip Jar. Visa/MC/Paypal accepted.
View over 750 of my fine art photos any time for free at DesktopScenes.com!

[ The PC Guide | Troubleshooting and Repair Guide | The Troubleshooting Expert | Troubleshooting Specific Components | 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.


  • 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.

Home  -  Search  -  Topics  -  Up

The PC Guide (http://www.PCGuide.com)
Site Version: 2.2.0 - Version Date: April 17, 2001
Copyright 1997-2004 Charles M. Kozierok. All Rights Reserved.

Not responsible for any loss resulting from the use of this site.
Please read the Site Guide before using this material.
Custom Search