Drives in a computer system represent storage, and there are many different types. As with everything else, the field of drive types is evolving constantly, but we have been in a relatively stable environment for the past couple years with SATA (or Serial ATA) drives taking up most of the desktop market.
SATA drives come in multiple flavors as well, but for the most part as of this writing, you will likely be purchasing a SATA II hard drive that runs at 7,200 rpm (revolutions per minute) and transfers data back and forth from the computer system at 3 Gbps (gigabits per second). There are drives that run as fast as 15,000 rpm, or drives that transfer as fast as 6 Gbps, but unless your custom build is going to be doing the most demanding multimedia work, you’re probably not going to need the extra expenses that these faster drives offer (usually at double the cost of comparable drives.)
Why buy one when you can have two at twice the price?
Serial ATA (SATA) Connectors. Image via Wikipedia
If you’re in the market for multiple drives, you might consider a smaller, faster drive to hold the boot partition of your operating system, which is commonly referred to as the boot drive. Separating the operating system from your other applications can usually produce performance boosts, and sometimes quite substantial. These boot drives will typically both run faster and transfer faster than their larger brethren, but at the cost of smaller sizes and heftier prices.
Another consideration for both protection and performance enhancement are redundant arrays of inexpensive disks, or RAIDs. There are multiple types of RAIDs that each offers different levels of performance and/or protection, from simple mirroring (anything written to one disk is automatically also written to the other) to data striping (writing sequential segments of data across multiple drives) to simple spanning (combining multiple drives into one large drive) or any combination of the three.
All of these options are usually beneficial, though how any might benefit your system the most depends heavily on what your computer will be used for, but I generally recommend against simple drive spanning, as losing a single drive in a group can render all the data in the group of drives useless. RAID 5 and 10 arrays tend to be the most beneficial in most cases, but generally involve a compliant controller card and at least 4-6 drives to implement. Obviously, such arrays must be considered carefully in regards to which power supply and computer case that you purchase.
Keep ‘em cool
Hard drives work much like a record player of old, spinning internal platters very fast while a sensor on an arm over the platters reads and writes the data magnetically. Especially for 10,000 and 15,000 rpm drives, it is imperative that the drives be included in the system cooling plan, because these drives can run extremely hot even under light loads. For 10k and 15k rpm drives, give serious consideration to using a hard drive cooling fan.