RAID is a way of combining multiple disk drives into a single entity to improve performance and/or reliability.
Software RAID operates on a partition-by-partition basis, where a number of individual disk partitions are ganged together to create a RAID partition. This is in contrast to most hardware RAID, which gang together entire disk drives into an array. There are many things which act as major factors.Operating system is one of them as far as RAID is concerned.
Many motherboards have already built in RAID controllers, but not all of these are suitable for fileserver applications. Most of them only support the simple modes 0 and 1.
If high capacity is first priority, the common option is a RAID 5, which distributes data to all array members and adds rotating parity information, too.
So, why not use the RAID 5 software option? RAID 5 that Windows Server offers can include all existing drives, rendering a RAID 5 controller unnecessary. However, if you only need file services, not even the expensive Windows Sever license is needed, since WindowsXP is capable of sophisticated RAID functions after only a few modifications.