windows xp - What do LowerFilters and UpperFilters CD/DVD driver registry settings do?

I am having trouble with a NEC ND-6650A DVD/CD drive not being recognized on Windows XP. The Device Manager gives me:

Windows cannot load the device driver for this hardware. The driver may be corrupted or missing. (Code 39)

Trying to install the driver gives the following message:

Target NEC ND-6650A is not found correctly

I have found several sites such as

http://www.computing.net/answers/hardware/cant-install-dvd-rrw-driver/60310.html

http://support.microsoft.com/kb/894730

suggesting I delete the LowerFilters and UpperFilters registry values from

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class{4D36E965-E325-11CE-BFC1-08002BE10318}

Before I make these changes, I would like to learn exactly what these specific settings are doing. (I'm a CompSci major, so I can handle the details :)

I have checked on the manufacturer's website, but I cannot find any documentation of what these entries are doing. (As mentioned here: Windows 7 Registry Settings Documentation)

Answer

See http://djlizard.net/2007/04/30/230/ for a brief explanation of filter drivers. In short:

• Upper filter drivers go between the operating system and the main driver, and lower filter drivers go between the main driver and the hardware.




• Each of the filter drivers should be present in C:\Windows\System32\Drivers with a .sys extension.




• You need and should only remove filter drivers that are causing a problem or do not exist on the system, leaving no blank lines and keeping each driver on its own line. Otherwise, as the Microsoft article says, you will have to reinstall programs such as CD burning software and iTunes.