Hard disks use one or more metal or glass platters covered with a magnetic coating. For more details, see SATA, SAS, SCSI and hard disk interfaces. Today, SATA drives are the most common, although SAS drives are also used. Over the years, several kinds of hard disks have emerged. For more details on disk structure, see magnetic disk, format program, hard disk defect management and drop protection. Hard disks are pre-formatted at the factory, which divides the platters into identifiable sectors. See hard drive capacity, access time and transfer rate. This mechanical action is why hard disks are slowly fading into history and being replaced with SSDs (see SSD). The platters rotate constantly at thousands of RPM however, to preserve battery, laptops default to powering them down after a set period of no activity. By comparison, CDs/DVDs take 80 to 120 ms. Speed is measured by transfer rate in megabytes per second as well as latency: how long it takes to begin transferring data, typically 3 to 15 milliseconds (ms). memory.Ĭapacity is measured in bytes, and the largest drives hold up to 10 terabytes. For a summary of memory and storage types, see storage vs. To learn how this workspace is used to process data, see memory. Disks store programs and data until deliberately deleted by the user, but memory (RAM) is a temporary workspace.
Hard disks are not the computer's main memory. In the past, removable cartridges for backup and transport contained the platters (see removable disk). Hard disks are "fixed disks," which means the platters reside permanently in the drive.
External hard disks can be plugged into USB or a eSATA port for more storage. Although the terms "hard disk" and "hard drive" are used synonymously technically, the disk spins inside the drive.Īll computers used to have an internal hard disk for storage however, today, storage can be solid state (see SSD).
#Hard disk drive definition free
This article is provided by FOLDOC - Free Online Dictionary of Computing ( ) hard diskThe primary computer storage medium, which is made of one or more aluminum or glass platters, coated with a ferromagnetic material.
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