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[ The PC Guide | Systems and Components Reference Guide | Hard Disk Drives | Hard Disk BIOS and Capacity Factors | Overcoming BIOS Disk Size Barriers ]

Software Translation Drivers (Dynamic Drive Overlays)

I always suggest that those who are trying to overcome a hard disk size barrier, first attempt to correct the problem through a free BIOS upgrade, if possible. If that's not an option for whatever reason, however, you will have a key decision to make in choosing between the other alternatives I am presenting: do you want to spend money on a hardware solution, or go with a "free" software solution?

For those who can afford to do so, I strongly recommend a hardware solution, such as an expansion BIOS card, an add-in controller card, or a third-party (not free) BIOS upgrade. The reason is simple: these solutions get around the hard disk barrier at a very low level within the system, and in doing so ensure that you will have few problems using your new hard disk on your old system. There are not likely to be any software issues with such a solution.

If you cannot spend funds on a hardware solution (or simply don't want to for whatever reason) then your alternative to allow access to the full capacity of your hard disk is the use of a software translation driver, also called a dynamic drive overlay or DDO. These usually go by names like Disk Manager, EZ-Drive and the like. The idea behind one of these programs is pretty simple: they override in software some of the BIOS code in your motherboard or hard disk controller, allowing access to the full size of a new hard disk on an older system. The software must be loaded immediately when the machine is booted, to ensure that the driver is in place before any other piece of software tries to access the disk. Otherwise, the disk will not work properly. To ensure that they are always loaded immediately at boot time, the installer for this sort of program modifies the boot disk's master boot record and installs the driver at the beginning of the disk.

When you buy a new hard disk at retail, the drive manufacturer will often include a copy of one of these driver programs, "free", with the drive. (You can often download them for free from the drive maker's web site too.) These are normally a specially modified version of something like Ontrack's Disk Manager that is customized for that manufacturer's drives; these utilities normally have proprietary names as part of the licensing agreement between the drive maker and the company that writes the overlay. Drive manufacturers provide these as a convenience for those whose machines don't have real hardware BIOS support for larger disks, and using them is a viable option.

However, do not believe these manufacturers when they sometimes say that using these software drivers is as good as proper BIOS support. It isn't. There are numerous problems associated with using these drivers for large disk support, which is why I do not recommend their use. Here are just a few:

  • Compatibility Problems: When you use one of these drivers they essentially set up their own logical disk volumes using a non-standard format. This means you are not using your disks the standard way. This isn't usually a problem in and of itself, since most operating systems know about these drivers, but the potential for incompatibility exists.
  • Reduced Drive Interoperability: The drivers that come with the various manufacturers' drives are normally customized for that manufacturer's equipment only. This means that if you put a Quantum disk in your PC and later want to add a Seagate, for example, you may have a bit of a problem. You will have to at this point probably purchase the full version of something like Disk Manager, and for the extra cost you will be better off buying an add-in hard disk controller.
  • Problems Removing the Driver: Some of these overlays can be very difficult to remove from the disk, and require you to use uninstall facilities that come with the driver, if you want to get rid of them. When you do remove the driver, say because you have upgraded to a PC that supports large drives, you may have to repartition and reformat the disks (though this may not be required).
  • Floppy Disk Booting Complications: Because the driver is located on the hard disk, you must boot from the hard disk to load it. If you boot from a floppy, your hard disk may seem to "disappear" because the overlay wasn't loaded. The driver will allow you to boot from a floppy, but you must do it by booting the hard disk, waiting for the overlay to load and a message to be displayed that says "To boot from a floppy disk, press the space bar", and then put the floppy into the drive and press the space bar.
  • Operating System Installation Issues: The drive overlay located on the hard disk can cause problems when using alternative operating systems, attempting to set up a multiple-OS system, and so on. You must verify that every operating system that you install is capable of handling the driver you are using.

Again, most of the time these drivers will work OK, especially if you are not doing anything too unusual with your PC. With so many people upgrading older systems and running into size barriers, they are becoming more prevalent than ever. I just think that they are not the best way to deal with BIOS translation, given that much more reliable, and relatively inexpensive, hardware solutions exist. It's all a matter of your priorities, really.

Next: Disk Size Reduction Jumpers

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