Being of unequal capacity, unequal performance, different brands, and the WD not being an RE ( RAID edition ), I would keep them seperate for maximum performance and stability. Normally I would encourage RAID 1 on a workstation build, but unless redundancy is absolutely needed, I cannot in this case. Splitting OS and Program Files up on seperate partitions on 2 different spindles will yield more performance in a desktop environment. Split your page file between the 2 drives also if you're using windows. XP and up is very good at using whichever drive has the the least activity for swapping, and splitting it up will give you the best of both worlds. I would suggest OS, AV, and other "system" programs on the seagate, and large programs ( such as games) on the WD. Always follow the "every-other" style when laying out your partions. If your program runs on the seagate, then it's data files should be on the WD, and vice-versa. I never use RAID until I have more than 3 drives accessible in a system, 1 for OS, 1 for Program Files, and 1 for Storage. If HDD failure is a concern, manually backing up data to alternate spindles is a viable option. Standard fire, lightning, theft, and Id10t disclaimers apply here as well. Always have offline back-up for those "whoops" scenarios. Even throwing all-caution-to-the-wind and going with RAID 0 would not be recommended in this case.