What Is a Hard Drive Used For?

By Jason Isbell

Hard drives store data for your computer. Like closets, they can be filled with stuff. However, unlike closets, computers know where everything is and can retrieve data--assuming everything is working properly.


Without a hard drive, a modern computer cannot function. The hard drive holds the installed programs, data files, operating system files and archives found on a computer. When the computer needs them, it reads them off the hard drive and uses them. If it is a data file, the computer might change the file and then save it again.


Modern hard drives come in two flavors, ATA and SCSI. ATA is the most commonly used format, as it is less expensive to produce. SCSI is used commonly in servers, as your can run more of them on one computer; they are faster and are often more durable.


Nearly every computer can run an ATA drive, but there are different interfaces for desktops than there are for laptops. Only servers commonly come with an SCSI interface.

Physical Size

Early hard drives had 8-inch platters and measured more than 9 inches across. Some hard drives now have smaller than 1-inch platters and measure less than an inch across. The most common sizes are the 3.5-inch desktop drive and the 2.5-inch laptop drive.


Space on hard drives is measured in bytes. Modern drives are measured in gigabytes or terabytes, while older drives were measured in megabytes. A megabyte is 1,024 bytes, a gigabyte 1,024 megabytes (1,048,576 bytes) and a terabyte is 1,024 gigabytes (1,073,741,824 bytes).


Faster drives mean faster processing. A drive running at 5,200 RPM is standard. If you pay a little more, you can get 7,200 RPM. If you have a server and need real speed, you can pay more and get 10,000 to 15,000 RPM.