question on partitioning, disk mirroring etc

my comp needs to handle a couple of databases ( tons of HH obv). i use a scanner for table selecting and one player told me to have like 2 drives, 1 exclusively for the OS and 1 for your db. he says it speeds up postgres searches and i would really like to see an improvement in speed with postgres, my computer is pretty fast and memory is topnotch but im just not sure if putting the os on a sep drive and the dbs on the other would really make a huge difference in speed, i need some opinions from people who know these things better. fwiw im using a caviar black 1tb and planning to buy a slightly slower 500gb caviar western digital blue just for the OS. im kinda confused now lol. any input/advice would be greatly appreciated. thx.

basically my question would be, does 2 drives beat like 1 partitioned drive in speed when it comes to databases etc?

yes, db on a separate disk a good idea. splitting db data files and log files into separate disks is another speedup. You should ask in a specific forum, because if you dont have much OS-related I/O , it MAY turn out that putting Log+OS on one disk and the data files on another is the best solution (granted you have 2 disks).

it would make a difference although im not sure how much.

also, if you're doing this, might as well get a classy harddrive with maximum rpms otherwise it seems less useful.

yeah caviars are decent. i was thinking about buying a 64gb SSD (solid state drive) coz they are the fastest really, but meh costs too much

Not sure it would make that much of a difference tbh, different partitions can help you make backups/disk images though