If I'm running a Raid 5 and I currently have 3 hdd's installed and I decide to insert another hdd..does windows automatically format that drive for me? What if there were 4 hdd's installed and I insert 2 more hdd's... and so fourth.. I really want to understand the logic on this. Thank you

Windows will not do anything to a drive automatically - except maybe give it a drive letter if it is already formatted. Depending on the type of RAID array you have and on how that RAID is implemented (software vs. hardware) will determine how you would add a disk. Typically once you have created a RAID array, you cannot add another disk to the RAID (with the exception of replacing a disk in the array). If you are using the software RAID in Windows that is always true - to my knowledge. With hardware RAID you may be able to add a disc to the array IF the hardware controller/drivers allows it. These tend to be more expensive than the RAID cards that do not allow drives to be added. Plus the process to add a drive can be a lengthy process. So, most likely, if you want to add drives to your RAID-5 array, you will need to back up the data, destroy the RAID array and recreate a new array with the additional disks. Michael J