Hard drives haven’t changed much in the basics of their design. Although the basics are the same, many advancement allow modern drives to perform faster and pack in more data than ever before.

Inside the airtight case is a dirt free environment, which is essential for the close tolerances that are found in the hard drive itself. The basic design consists of a number of discs, called platters, which are stacked above each other, with a bit of a gap between, and spin on the spindle. There can be up to five platters, but there is usually only one. Each platter has a surface that can be read from or written to, but a little arm that extends over the surface. The head at the end of the little arm performs the task of reading and writing. It’s almost like a record player, except the head never touches the surface.

All drives have this basic design, but push current technology and utilize new technologies to get the most from the drives. One thing to note right from the start is that drives from two different manufacturers that carry the same specifications will almost always have similar performance.

Drives very in size from the standard 1 inch high models found in desktops down to smaller 12.5mm and 9.5mm models found in laptops and even smaller sizes found in smaller devices.

The number of platters depends on the use of the drive. Usually there is only one platter, which reduces the number of moving parts, namely the arms and heads, resulting in less chance of drive failure. Multiple platters allow for larger storage capacity. Laptop drives can have up to two platters. Desktop drives have usually have 3.5 inch platters, enterprise hard drives look like 3.5 inch drives, but have 2.5 inch platters inside. Mobile drives have 2.5 and 1.8 inch platters, while some micro-drives use 1 or 0.8 inch platters.

Spindle speed, which is how fast the platters spin in the drive, makes a huge difference to the performance of the drive. Think about it, the faster it can spin, the faster the information that is being looked for will pass beneath the read/write heads, it’s just quicker. Server and wordstation drives often spin at 10,000 or 15,000 RPM, while dekstops typically spin at 7200 RPM, although the WD Raptor is a notable exception that spins at 10,000 RPM. However the price of a Raptor is very high and you pay more for its 150 GB model than for a 500 GB drive.

Notebook drives are traditionally 4,200 RPM, but are slowly being replaced by 5,400 RPM models. Smaller mobile drives operate at 4,200 RPM, while the micro-drives operate even slower.

Cache makes a huge difference by storing frequently accessed data in a fast storage area so that there is no physical read from the disc. Currently you can get up to 16 MB of cache on a hard drive, but there is no great performance benefit over 8 MB of cache which tends to be the best choice.

Although drive may vary a little in their speed, the biggest benefit will come from high RPM drives like the WD Raptor family. For most other drives, divide the price by the size of the drive in GB and compare drives that way to get the best value per GB.