Depends on you BIOS and what OS'es you want to install. If your BIOS lets you choose between IDE-0 through 3 or something then you can use the BIOS to switch Operating System bootups. If you have an older OS already installed then you can install XP or another operating system and let the OS set up a Dual Boot situation for you. The general rule is that the OS'es need to reside on seperate partitions or Hard disks, and if you want to dual boot then you need to install them by age. If you want to mix and match 98 and XP then you need to look at Filesystems that are compatible with both.
RAID stands for Redundant Array of Independent (or inexpensive. Depends on who you ask) Disks.
There are several levels of RAID, but the 3 major ones are:
RAID 0, also known as striping. Needs at least 2 disks. What happens with this level is that the drives are written to in alternation. Disk one gets a stripe of information then disk two gets a stripe of information, and then back to disk one, and so on... The benefits are that since the information is spread out over 2 or more disks then you get better perfomance because each disk is reading less and writing less. You also get to use the full capacity of each drive (keeping in mind that you need to match the capacity and performance level of drives to each other). The downside is that if you lose a harddisk to failure then half of your information just died too, leaving the good half useless.
RAID 1 (mirroring): its called mirroring for one obvious reason....the drives are mirrored. Almost exact replicas. If you lose a mirrored drive its not a big deal. Drawbacks are that its actually slower than a single drive for write access and read benefits are negligible. Two or more drives needed. Capacity is also limited to the smallest drive's capacity.
RAID 5 (striping with parity): This resembles RAID 0 in several ways, but the main difference is that on each drive parity information is stored. In the case of drive failure the computer will use the parity information to rebuild the dead disk, once its replaced with a new drive. Since it is striped you also get great read speed and write speed is slightly better than average. Disk space used for parity is a fraction of the total drives in the system. For example, if I had 3 drives (the minimum in a RAID 5) I would have 1/3 of the space devoted to parity and the other 2/3 available to use. If i had 10 drives it would be 1/10th, and so on...
RAID 5 is the most favored in corporate use because it gives you performance with redundancy. RAID 0 is the most poplular for the average guy like you and me. RAID 1 is sometimes useful, mostly not.
