Hard Drive Construction

• With the exception of Solid State Drives (SSDs), every hard drive uses the same basic physical design. Inside the drive is a stack of thin discs called platters. Data is stored and retrieved from these platters by a seek arm that moves up and down the surface of the disc. As the seek arm moves, the platter spins beneath it at high speeds. The combination of the spinning disc and the movement of the arm allows data, which is not necessarily stored sequentially on the disc, to be accessed regardless of its physical placement.
  
  

RPMs

• The four digit number displayed in a hard drive's name refers to the drive's physical speed in revolutions per minute (rpm). This is the number of times the platters are able to make a full rotation in a single minute. The higher the rpm, the more quickly that data can generally be accessed, increasing data transfer speeds and your computer's performance during heavy hard drive activity, such as transferring a large file or launching an application.
  
  

Other Factors

• RPMs alone do not depict the quality and performance of a hard drive, though they do play a large part. When comparing two hard drives, such as a 4200 and a 5400 RPM Serial Advanced Technology Attachment (SATA) drive, the seek time and the data throughput must also be considered. The seek time is the amount of time that a drive requires to move the arm into position to access the data. While the seek time on a high RPM drive is typically faster, this is not always the case. A cheaper 5400 RPM drive may have a higher -- and therefore, slower -- seek time than a more expensive 4200 RPM drive. Data throughput is how much data a hard drive can process at once. Higher data throughput refers to a drive's ability to communicate larger chunks of data simultaneously, resulting in better performance.
  
  

Comparison

• Based on the physical mechanics of hard drives, a 5400 rpm drive will almost always be faster than a 4200 rpm drive. Though this is rarely the case, a 5400 rpm drive may have less data throughput or a longer seek time than a physically slower drive, resulting in lower performance than a 4200 rpm drive. For this reason, all components of the two drives should always be compared. For example, the faster spinning 5400 rpm drive does produce more heat and use more battery life than the 4200 rpm, both of which are important factors when the drive is installed in a laptop. Most hard drive manufacturers take this into account, however, and include power saving features on faster drives, nullifying the efficiency difference and giving the 4200 rpm drive no advantage under these circumstances.