A hard drive stores all your data, where all your files and folders are physically located. A typical hard drive is slightly larger than your hand, yet can hold over 100 GB of data. The data is stored on a stack of disks mounted inside a solid encasement. These disks spin extremely fast (typically at either 5400 or 7200 RPM) so that data can be accessed immediately from anywhere on the drive. The data is stored on the hard drive magnetically, so it stays on the drive even after the power supply is turned off.
The term “hard drive” is actually short for “hard disk drive.” The term “hard disk” refers to the actual disks inside the drive. However, all three of these terms usually refer to the same thing. The hard disk drive definition is the place where your data is stored.
A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electromechanical data storage device that uses magnetic storage to store and retrieve digital information using one or more rigid rapidly rotating disks (platters) coated with magnetic material. The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a random-access manner, meaning that individual blocks of data can be stored or retrieved in any order and not only sequentially. HDDs are a type of non-volatile storage, retaining stored data even when powered off.
The first production IBM hard disk drive, the 350 disk storage, shipped in 1957 as a component of the IBM 305 RAMAC system. It was approximately the size of two medium-sized refrigerators and stored five million six-bit characters (3.75 megabytes) on a stack of 50 disks.
In 1962, the IBM 350 was superseded by the IBM 1301 disk storage unit, which consisted of 50 platters, each about 1/8-inch thick and 24 inches in diameter. While the IBM 350 used only two read/write heads,[28] the 1301 used an array of heads, one per platter, moving as a single unit. Cylinder-mode read/write operations were supported, and the heads flew about 250 micro-inches (about 6 µm) above the platter surface. Motion of the head array depended upon a binary adder system of hydraulic actuators which assured repeatable positioning. The 1301 cabinet was about the size of three home refrigerators placed side by side, storing the equivalent of about 21 million eight-bit bytes. Access time was about a quarter of a second.
A modern HDD records data by magnetizing a thin film of ferromagnetic material on both sides of a disk. Sequential changes in the direction of magnetization represent binary data bits. The data is read from the disk by detecting the transitions in magnetization. User data is encoded using an encoding scheme, such as run-length limited encoding, which determines how the data is represented by the magnetic transitions.
A typical HDD design consists of a spindle that holds flat circular disks, called platters, which hold the recorded data. The platters are made from a non-magnetic material, usually aluminium alloy, glass, or ceramic. They are coated with a shallow layer of magnetic material typically 10–20 nm in-depth, with an outer layer of carbon for protection. For reference, a standard piece of copy paper is 0.07–0.18 mm (70,000–180,000 nm) thick.
The amount of storage on a hard disk is measured in gigabytes and terabytes. Hard drive capacity is measured by the amount of data users need to store, which is often much greater than the space applications take up. For example, a single video can take up four gigabytes of space.
In 1957, the cost of one megabyte of storage on the first hard drive would be the equivalent of USD $200,000 in today’s dollars. However, in 2017, one megabyte of hard drive storage costs less than 1/3000th of one cent! See hard disk, byte, SSD, and space/time.
A hard disk is the primary computer storage medium, which is made of one or more aluminum or glass platters, coated with a ferromagnetic material. Although the terms “hard disk” and “hard drive” are used synonymously; technically, the disk spins inside the drive.
All computers used to have an internal hard disk for storage; however, today, storage can be solid-state (SSD). External hard disks can be plugged into a USB or an eSATA port for more storage.
1-Storage vs. Memory
Hard disks are not the computer’s main memory. Disks store programs and data until deliberately deleted by the user, but memory (RAM) is a temporary workspace. To learn how this workspace is used to process data, see memory. For a summary of memory and storage types, see storage vs. memory.
2-Capacity and Speed
Capacity is measured in bytes, and the largest drives hold up to 10 terabytes. 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). By comparison, CDs/DVDs take 80 to 120 ms.
A byte (BinarY TablE) is the common unit of computer storage from a desktop computer to mainframe. It is made up of eight binary digits (bits). A ninth bit may be used in the memory (RAM) circuits as a parity bit for error checking.
A byte holds one alphabetic character such as the letter A, a dollar sign, or decimal point. For numeric data, one byte holds one decimal digit (0-9), two “packed decimal” digits (00-99), or a binary number from 0 to 255.
IBM coined the term in the mid-1950s to mean the smallest addressable group of bits in a computer, which was originally not eight. The first spelling of the word was “bite,” but they was added to avoid misspelling between “bit” and “bite.” There are eight binary digits (bits) in a byte, but there can also be nine bits per byte in RAM cells that include error correction.
Drives and memory (RAM) are rated in bytes. For example, a 512-gigabyte (512GB) drive stores 512 billion characters of program instructions and data permanently, while eight gigabytes (8GBs) of RAM holds eight billion temporarily. The first hard drives in early personal computers held 5MB, and RAM was 64K.
A SSD (Solid State Drive) is an all-electronic non-volatile storage device that is an alternative to, and is increasingly replacing, hard disks. Employed in myriad products, including mobile devices, iPods, cameras, laptops, and desktop computers, SSDs are faster than hard disks because there is zero latency (no read/write head to move). They are also more rugged and reliable and offer greater protection in hostile environments. In addition, SSDs use less power and are not affected by magnets.
In time, there will only be solid-state storage, and spinning disk platters will be as obsolete as the punch card.
SSDs are made of flash memory chips 99% of the time. However, for the absolute fastest storage speed obtainable, there are SSDs that use volatile RAM chips backed up by non-volatile storage in case of power failure.
In its simplest form, an SSD is flash storage and has no moving parts. As a result, they’re smaller and take up less space in a PC case, in some instances even mounting directly to the motherboard. SSD storage is much faster than its HDD equivalent.
HDD storage is made up of magnetic tape and has mechanical parts inside. They’re larger than SSDs and much slower to read and write. In its simplest form, an SSD is flash storage and has no moving parts.
The primary characteristics of an HDD are its capacity and performance. Capacity is specified in unit prefixes corresponding to powers of 1000: a 1-terabyte (TB) drive has a capacity of 1,000 gigabytes (GB; where 1 gigabyte = 1 billion bytes).
The common prefixes are as follows: Kilobyte (KB) = 1,024 bytes. Megabyte (MB) = 1,024 kilobytes or 1,048,576 bytes. Gigabyte (GB) = 1,024 megabytes or 1,073,741,824 bytes.
Multiple best practices must be followed to improve the performance of an HDD:
Hard disk drive storage capacity
Some of the most common storage drive capacities include the following:
- 16 GB, 32 GB and 64 GB. This range is among the lowest for HDD storage space and is typically found in older and smaller devices.
- 120 GB and 256 GB. This range is considered an entry point for HDD devices such as laptops or computers.
- 500 GB. Most computer users have 500 GB or more disk drive storage. With this much space, users can most likely store all their music, photos, videos and other files.
- 1 TB and 2 TB. Individuals with games that take up a lot of space need 1 TB to 2 TB of HDD space.
- More than 2 TB. Users who work with high-resolution files need more than 2 TB of disk space. This is also a requirement for people who need to store or house a large amount of data, or who want to use that space for backup and redundancy.
The highest capacity HDD available is 36 TB. However, an HDD has less usable space than advertised because the OS, file system structures and some data redundancy procedures use a portion of the HDD. Enterprise use of disk drives, such as for large-scale file collections, can require anywhere from a few terabytes to the maximum number of terabytes on an HDD. Home office users often require less than a terabyte.
Hard drive components and form factors
Hard disk drive components include the spindle, disk platter, actuator, actuator arm and read/write head. Even though the term hard disk drive is used to refer to the unit as a whole, the term hard disk is the set of stacked disks. This is the part of the HDD that stores and provides access to data on an electromagnetically charged surface.
The HDD http://www.techtarget.com/whatis/definition/form-factor refers to the physical size or geometry of the data storage device. HDD form factors follow a set of industry standards that govern their length, width and height, as well as the position and orientation of the host interface connector. Having an industry-standard form factor helps determine a common compatibility with different computing devices.
The most common form factors for HDDs in enterprise systems are 2.5-inch and 3.5-inch -- also known as small form factor and large form factor. The 2.5-inch and 3.5-inch measurements represent the approximate diameter of the platter within the drive enclosures.
While there are other form factors, by 2009, manufacturers discontinued the development of products with 1.3-inch, 1-inch and 0.85-inch form factors. The falling price of flash memory and flash drives made these other form factors almost obsolete. It's also important to note that while nominal sizes are in inches, actual dimensions are specified in millimeters.
Many solid-state drives are also designed for the HDD form factor. http://www.techtarget.com/searchstorage/definition/SSD-solid-state-drive that fit into the same slots as HDDs generally use the SATA interface or http://www.techtarget.com/searchstorage/definition/serial-attached-SCSI, also known as a SAS interface, to transfer data to and from the host computing system.
What are external HDDs?
Most HDDs are internal hard drives inside a computer and work as described above. However, external hard drives are also available to expand a computer's storage capacity or act as a portable device to back up data. External drives connect to a computer or device through interfaces such as USB 2.0, USB-C or with external SATA. External hard drives might also have slower data transfer rates compared to internal HDDs.
The main advantage of an external hard drive, in addition to expanding a device's storage space, includes being portable. Users can store data from multiple devices and physically bring that data with them wherever they go.
Common hard disk errors
https://www.techtarget.com/searchstorage/answer/Whats-the-best-way-to-protect-against-HDD-failure for all sorts of reasons. However, failures generally fall into the following six categories:
- Electrical failure occurs when, for example, a power surge damages a hard disk's electronic circuitry, causing the read/write head or circuit board to fail. If a hard disk powers on but can't read and write data or boot, it's likely that one or more of its components has suffered an electrical failure.
- Mechanical failure can be caused by wear and tear, as well as by a hard impact, like a hard drop. This might cause the read/write drive head to hit a rotating platter, causing irreversible physical damage.
- Logical failure results when the hard disk's software is compromised or ceases to run properly. All sorts of data corruption can lead to logical failure. These include corrupt files, malware and viruses, improperly closing an application or shutting down a computer, human error or accidentally deleting files that are critical to hard disk functionality.
- Bad sector failure can occur when the magnetic media on a hard disk's rotating platter is misaligned, resulting in a specific area on the platter becoming inaccessible. Bad sectors are common and often limited when they occur. Over time, the number of bad sectors can increase, eventually leading to a system crash, inaccessible files or the hanging or lagging of the operation of a hard disk.
- Firmware failure happens when the software that performs maintenance tasks on a drive and enables the hard disk to communicate with a computer becomes corrupted or stops working properly. "https://www.techtarget.com/whatis/definition/firmware" failure can lead to the disk freezing during bootup or the computer a hard disk is connected to not recognizing or misidentifying it.
- Multiple unknown failures that accumulate over time can also occur. For example, an electrical problem could lead to a mechanical failure, such as a read/write head crash. It might also lead to a logical failure, resulting in several bad sectors developing on the hard disk platters.
History and technical evolution of HDDs
Some significant milestones in the development of hard disk drives include the following:
- 1953. IBM engineers created the first hard disk as a way to provide random access to high capacities of data at a low cost. The first disk drives were the size of refrigerators, could store 3.75 MB of data and began shipping in 1956. Memorex, Seagate Technology and Western Digital were other early vendors of hard disk drive technology.
- 1980s. Hard disk drive form-factor size decreased as the technology evolved. By the mid-1980s, 3.5-inch and 2.5-inch form factors were introduced and became standard in personal computers. Hard disk drive density has increased since the technology was first developed. The first hard disk drives could store https://www.techtarget.com/searchstorage/definition/megabyte of data, while today their storage capacity is in the terabyte range.
- 2007. Hitachi Global Storage Technologies (HGST) -- now a Western Digital brand -- released the first 1 TB hard drives in 2007.
- 2012. HGST announced the first helium-filled hard disk drive in 2012. Helium is less dense, cooler and lighter than air, consumes less power, increases drive density and improves performance compared to traditional hard disk drives.
- 2013. Seagate Technology announced hard disk drives that use shingled magnetic recording technology. SMR increases storage density in HDDs by layering the magnetic tracks on each disk, rather than placing them parallel to each other. It's referred to as shingled because the tracks overlap similar to shingles on a roof.
- 2015. HGST announced the first 10 TB hard drive.
- 2018. Western Digital released the Purple 12TB with AllFrame AI-powered technology for surveillance and security systems.
- 2021. Western Digital unveiled two 20 TB HDDs -- the Ultrastar DC HC560 and WD Gold HDD Enterprise Class SATA HDD. The Ultrastar DC HC560 was designed for cloud storage providers and business servers, security systems and network-attached storage devices. The WD Gold HDD was designed for enterprise businesses that run heavy application workloads.
- 2025. Seagate releases its Exos series HDDs which can store 36 TB of data.