Laptop Vs. Desktop Hard Drives

Historically, desktop computers used 5.25-inch hard drives, but today's desktops primarily rely on 3.5-inch drives. This size allows for several internal platters, increasing the drive's storage space. These drives, however, are too heavy and thick to use in portable computers. Instead, most laptops use 2.5-inch drives. These hard disks are lighter, slimmer and use less energy -- a premium when running on batteries. Though commonly installed in devices such as iPods, 1.8-inch drives are also used in some ultra-thin laptops and netbooks.

The physical thinness of 2.5-inch laptop drives directly affects their storage capacity. With less room internally, 2.5-inch drives contain fewer, smaller platters. While some high-end 3.5-inch drives boast 4TB of storage -- and continue to grow -- laptop drives cannot match this claim. Instead, even the most expensive laptop drives often range in size from 750GB to 1TB. While laptop drives also get larger year after year, their physical size prevents them from ever catching up to the space provided by desktop drives.

In order to read and write data, the platters in hard drives spin rapidly. While some enthusiast drives run at 10,000 rotations per minute, the majority of desktop hard drives run at 7,200 RPM. In order to keep down heat, power use and noise levels, many laptop drives run slower, at only 5,400 RPM. This decreased rotation speed directly affects the speed of the computer, as the drive has to spin for longer to reach each piece of data. However, some laptop models do include 7,200 RPM drives, negating the speed difference.

In the last several years, many laptop and desktop computers have begun including solid state drives instead of hard drives. These SSDs use data chips instead of platters, removing the noise, heat and vibration caused by hard drives. While more expensive than hard drives, SSDs also run significantly faster than even 10,000 RPM disks. Due to the price difference, some desktop computers include both a small SSD for frequently-used data and a large hard drive for greater storage capacity. Because most laptops can't fit two drives, some models offer hybrid drives, which have a large storage area in addition to a small SSD used for caching.

While 3.5-inch drives can't fit into most laptops internally, you can still connect them using an external enclosure, which you plug into your computer via a USB or external SATA (eSATA) cable. Similarly, you can use 2.5-inch drives on a desktop with an enclosure, or use a mounting bracket to install them internally. Some desktop computers also include 2.5-inch drive bays, since most SSDs are of this size.