Desktop PCs

A hard disk

Hard drive

The hard drive in your PC is a storage device, sort of like a digital briefcase where you keep all your important data. It works by rapidly recording data with magnetic pulses on spinning metal platters. The more quickly a drive spins, the quicker you can access and transfer data.

Hard drives come in a number of physical sizes, but 3.5in is by the far the most common type for PCs. Most PC cases are designed to fit 3.5in drives and most mid-tower-sized cases have multiple bays for multiple drives.

The hard drive contains a motor that spins the platters at speeds from 5400 to 15,000 revolutions per minute (RPM), although 7200rpm is the standard for many of today's desktop hard drives. The more quickly the drive spins, the more quickly you can read and store data. Western Digital's Caviar GP 'Green' drive is an exception. It spins slower than 7200rpm in a bid to reduce power consumption. While the spin speed can affect the overall performance of your PC, it's worth noting that even this slower drive performed well in our tests. Conversely, Western Digital also has a drive called the Raptor, which spins at 10,000rpm, but performance benefits can't be seen with this drive unless it's installed as part of a RAID configuration.

What sizes do hard drives come in?

The minimum size your hard drive will come in these days has risen significantly over the past couple of years, and consumers should be able to find a sub-$1500 desktop PC with between 200GB and 400GB of hard disk drive space. Drives with up to 1000GB storage are currently available, but they are a little less cost effective (when calculating their cost per gigabyte) than smaller drives. If you plan on storing large amounts of data on your hard drive, such as videos, digital images or multimedia files, then the bigger the hard drive, the better. Another option is to install multiple smaller hard drives. Actually, relatively large capacity drives are so inexpensive these days; it's worth buying at least two hard drives of the same size so that you can keep a backup of your data on the second drive. Alternatively, backups can be kept on an external hard disk. Note that the capacity of hard drives will always be reported differently in your operating system. For example, a drive that's marketed as having a capacity of 500GB, will have an actual usable capacity of 465GB. This is because hard drive vendors deem 1MB to be equal to 1000KB, but for a computer, 1MB is equal to 1024KB, so 24KB of extra space is required to make up the megabyte.

As an example of how much space typical files will consume, we've used a 500GB hard drive (which has a usable formatted capacity of 465GB) to illustrate the amount of storage space you'll need to house the following files:

  • Using near CD-quality MP3 files, encoded at 192Kbps, one minute of music will consume 1.4MB of space. A typical 74min CD will therefore consume 103.6MB. If you have a CD collection consisting of 200 CDs, then over 20GB of space will be required to store them.
  • Three PC games (such as Crysis, Company of Heroes and FEARI, at 7GB, 8GB and 5GB, respectively): 20GB
  • Two hours of DV footage: 25.60GB
  • 10 hours of recorded high-definition digital (15Mbps) TV shows: 64GB
  • Windows XP: 2GB
  • Two years of stored e-mail messages for a heavy user: 4GB
  • 11 applications, including Office XP Professional, Norton AntiVirus and Adobe Photoshop: 2GB
  • 317 10-megapixel JPEG photos (3872x2592 each): 1.22GB
  • Thousands of Excel spreadsheets, Word documents and Acrobat files: 6GB

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