A hard disk drive (sometimes abbreviated as Hard drive, HD, or HDD) is a datastorage device. The hard disk was first introduced on September 13, 1956 and consists of one or more platters inside of an air-sealed casing. Internal hard disks reside in a drive bay and connect to the motherboard using an ATA, SCSI, or SATAcable, and are powered by a connection to the PSU (power supply unit). Below is a picture of what the inside of a hard drive looks like for a desktop and laptop hard drive
.As can be seen in the above picture, the desktop hard drive consists of the following components: the head actuator, read/write actuator arm, read/write head, spindle, and platter. On the back of a hard drive is a circuit board called the disk controller.
How is data read and stored on a hard drive?
Data sent to and from the hard drive is interpreted by the disk controller, which tells the hard drive what to do and how to move the components within the drive. When the operating system needs to read or write information, it examines the hard drive’s File Allocation Table (FAT) to determine file location and available areas. Once this has been determined, the disk controller instructs the actuator to move the read/write arm and align the read/write head. Because files are often scattered throughout the platter, the head needs to move to different locations to access all information.
All information stored on a traditional hard drive, like the above example, is done magnetically. After completing the above steps, if the computer needs to read information from the hard drive, it would read the magnetic polarities on the platter. One side of the magnetic polarity is 0 and the other is 1. Reading this as binary data, the computer can understand what the data is on the platter. For the computer to write information to the platter, the read/write head aligns the magnetic polarities, writing 0’s and 1’s that can be read later.
External and Internal hard drives
Although most hard drives are internal hard drives, many users also use external hard drives to backup data on their computer and expand the total amount of space available to them. External drives are often stored in an enclosure that helps protect the drive and allow it to interface with the computer, usually over USB or eSATA. A great example of a backup external device that supports multiple hard drives is the Drobo.
External hard drives come in many shapes and sizes. Some are large, about the size of a book while others are about the size of a cell phone. External hard drives can be very useful for backing up important data and taking with you on the go since they usually offer more space than a jump drive and are still portable. The picture to the right is an example of a laptop hard disk drive enclosure from Adaptec. With this enclosure, the user installs any size of laptop hard drive they desire into the enclosure and connect it to a USB port on the computer.
HDD being replaced by SSD
Solid State Drives (SSDs) are starting to replace hard disk drives (HDDs) in many computers because of the clear advantages these drives have over HDD. While SSD is becoming more and more popular, HDD will continue to be in desktop computers with SSD because of the available capacity HDD offers over SSD.
1. Short for Revolutions Per Minute, RPM is used to help determine the access time on computer hard drives. RPM is a measurement of how many revolutions a computer’s hard drive makes in a single minute. The higher the RPM, the faster the data will be accessed; for example, if you were comparing two hard drives, one with 5400 RPM and another with 7200 RPM, the hard drive with a 7200 RPM will be capable of accessing data much faster than the other.
♠Note: Newer computers with SSD drives have no movable parts and therefore have no RPM.
Originally, the term RAID was defined as redundant array ofinexpensive disks, but now it usually refers to a redundant array ofindependent disks. RAID storage uses multiple disks in order to provide fault tolerance, to improve overall performance, and to increase storage capacity in a system. This is in contrast with older storage devices that used only a single disk drive to store data.
RAID allows you to store the same data redundantly (in multiple paces) in a balanced way to improve overall performance. RAID disk drives are used frequently on servers but aren’t generally necessary for personal computers.
How RAID Works
With RAID technology, data can be mirrored on one or more disks in the same array, so that if one disk fails, the data is preserved. Thanks to a technique known as striping (a technique for spreading data over multiple disk drives), RAID also offers the option of reading or writing to more than one disk at the same time in order to improve performance.
In this arrangement, sequential data is broken into segments which are sent to the various disks in the array, speeding up throughput. A typical RAID array uses multiple disks that appear to be a single device so it can provide more storage capacity than a single disk.