for all who knows please tell me....what is the purpose of IDE or LAN or RAID drivers to be installed in your computer?

I hope I am understanding your question. If I am telling you something you already know, I appologize.

Every piece of hardware in a computer needs a "driver" so your system knows how to use that piece of hardware. Without a driver, windows does not know how to use the hardware.

So in order to use IDE devices (cdrom, hard drives etc), you need the IDE drivers.
If you use a LAN interface, you need lan drivers
If you use Raid, you need the drivers...etc.

I hope this answers your question!