How About A RAID Setup?
Another advantage of splitting system and user data onto two different drives is the backup advantage. Why not copy your really important data from one drive to the other once in a while? Of course this cannot replace regular backups, but it adds a safety margin in case something horrible happens. In fact, the secondary, large hard drive could also be furnished with a complete image of your system drive. This will give you the option to use it as a transitional system drive until you are able to replace the defective system drive.
In this context we don't want to ignore the option to use two or more hard drives to build a RAID array. These so-called Redundant Arrays of Inexpensive/Independent Drives allow you to either improve performance by distributing reads and writes across all drives - RAID 0 striping - or increase data safety by mirroring data on a second drive in real time - RAID 1 mirroring. In the latter case, one of the drives failing will not have an effect on performance and will not cause a data loss. At the same time, a RAID 0 multiplies the risk of a data loss, because any of the two (or more) drives dying will kill the whole array and thus all of your data.
Many modern systems support RAID 0 or 1. Most likely, RAID will be handled by the mass storage controller(s) on motherboards that cost at least $ ~120; double-check the manual if you aren't sure. RAID 0 generally is the best choice if you require high data transfer rates; in fact, it is possible to almost double throughput numbers by deploying a RAID 0 configuration. However, access times do not improve, and sometimes you will even see an increase in access time. Your everyday life with Windows won't be accelerated much by using a RAID 0 array, even if many people tend to believe that! We have proof for this statement in the form of benchmark numbers that compare the WD1500 Raptor with a two-drive RAID 0 setup that consists of two 7,200 RPM drives.