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A HDD or “Hard Disk Drive” is the device that holds all of the information on your computer, including the operating system (“OS” such as Windows).
Traditionally (that is, until SSDs, discussed below), the drive is comprised of a hard metal disk (“platter”) and an actuator “arm” that is magnetically maneuvered across the spinning disk in order to access the information stored on the drive. The nearly weightless suspension arm hovers above the magnetic disk spinning as fast as 7,200 revolutions per minute. The arm holds a recording head the size of a pepper flake, which sits above the disk at a height measured in nanometers - less than the ridges of a fingerprint. Each disk drive contains more than 200 parts, most of them designed for specific models. Many of the suppliers are family-owned businesses that manufacture one-of-a-kind industrial molds or specialty chemicals. The data is retained on the disk even when the HDD is off (as opposed to cache or RAM). Until the summer, 2011 flooding in the northern area of Bangkok, Thailand where many of the plants are located which increased demand and therefore prices, hard drive prices had dramatically fallen. For example, a megabyte of storage in 1981 cost $40. In 2011, it had fallen to one-tenth of a cent!
Hard drives organize their user stored data into regions of the magnetic media called blocks. These blocks are, in turn, located in regions of the disk called a sector. These drive sectors are located along the concentric tracks on the surface of the disk. Within each sector is also located a servo and error correction information that allows the magnetic heads to stay on track so that they can read and write data, and for the electronic channel to recover the data without errors. The sectors also contain information that allows the file system to reassemble the data blocks into computer files. While a sector is the smallest unit that can be accessed on a hdd, a cluster is a slightly larger unit that is used to organize and identify the files on a disk. Most files take up several clusters of disk space. Each cluster has a unique ID, which enables the drive to locate all the clusters on a disk. After reading and writing many files to the hdd, some clusters may remain labeled as being used although they contain no data. These are called lost clusters and can be fixed using Windows Scan Disk or the Mac Utility program; also defragmentation can help free up additional hdd space. [Now you know what the report is talking about when you run the Windows ScanDisk utility.]
See also the definitions in the Glossary for the boot sector and the MBR (“Master Boot Record”), typically the first sector in the first partition in the drive which starts the operating system. And also for an understanding of S.M.A.R.T., the technology that monitors disk drives to warn about impending disk failure.
For the past 30 years, the size of the sectors on the hard drive was limited to 512 bytes for most OSs, including Windows and the ATA interface. Recently, Linux and other open-source developers have led a standards effort to create a 4,096 byte sector standard often referred to as the 4K sector. This 8x increase in sector size would increase formatting and operating efficiency of the newer, larger drives, especially by allowing for a more robust ECC (Error Correcting Code), critical to creating high area drive densities, and is probably long overdue.
HDDs come in different capacities, speeds and connections (e.g. IDE, SCSI, SATA; speeds starting at 5400rpm, then 7200 rpm [most common] then 10,000, 12,500 or even 15,000rpm for server drives; capacities from 40Gbs to 10 terabytes, the most common these days about 500Gb); See definitions in the Glossary. Also, read about Solid State Drives (SSDs) and Hybrid drives, which have both benefits and drawbacks. Click HERE for some interesting history about hard drives by PC World Magazine. Also, for those businesses that don’t want to protect their data by migrating it to the CLOUD, there are also lines of fire and flood resistent hard drives (offering, for example, 30 minutes of fire protection up to 1550 degrees fahrenheit and 72 hours of immersion protection in up to 10 feet of water. See ioSafe drives for between $250 - $600.
Finally, drives can get quite HOT. Particularly those on laptops. Make sure that they’re properly ventilated (and dust free), otherwise they may crash. That’s why many laptops must be put on cooling “pads” if they’re used all day - the heat will cause shut-downs.
See the LINKS page for a short history and deconstructed photos of an actual HDD like the one below:
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