Hard Disk (SATA, USB, Solid State) Innovation
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Wikipedia
A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating 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 and retrieved in any order. HDDs are a type of non-volatile storage, retaining stored data when powered off. Modern HDDs are typically in the form of a small rectangular box.
Introduced by IBM in 1956, HDDs were the dominant secondary storage device for general-purpose computers beginning in the early 1960s. HDDs maintained this position into the modern era of servers and personal computers, though personal computing devices produced in large volume, like cell phones and tablets, rely on flash memory storage devices. More than 224 companies have produced HDDs historically, though after extensive industry consolidation most units are manufactured by Seagate, Toshiba, and Western Digital. HDDs dominate the volume of storage produced (exabytes per year) for servers. Though production is growing slowly (by exabytes shipped), sales revenues and unit shipments are declining because solid-state drives (SSDs) have higher data-transfer rates, higher areal storage density, somewhat better reliability, and much lower latency and access times.
The revenues for SSDs, most of which use NAND flash memory, slightly exceeded those for HDDs in 2018. Flash storage products had more than twice the revenue of hard disk drives as of 2017. Though SSDs have four to nine times higher cost per bit, they are replacing HDDs in applications where speed, power consumption, small size, high capacity and durability are important. As of 2019, the cost per bit of SSDs is falling, and the price premium over HDDs has narrowed.
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 (109) bytes). Typically, some of an HDD’s capacity is unavailable to the user because it is used by the file system and the computer operating system, and possibly inbuilt redundancy for error correction and recovery. There can be confusion regarding storage capacity, since capacities are stated in decimal gigabytes (powers of 1000) by HDD manufacturers, whereas the most commonly used operating systems report capacities in powers of 1024, which results in a smaller number than advertised. Performance is specified as the time required to move the heads to a track or cylinder (average access time), the time it takes for the desired sector to move under the head (average latency, which is a function of the physical rotational speed in revolutions per minute), and finally the speed at which the data is transmitted (data rate).
The two most common form factors for modern HDDs are 3.5-inch, for desktop computers, and 2.5-inch, primarily for laptops. HDDs are connected to systems by standard interface cables such as PATA (Parallel ATA), SATA (Serial ATA), USB or SAS (Serial Attached SCSI) cables.
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 52 disks (100 surfaces used). The 350 had a single arm with two read/write heads, one facing up and the other down, that moved both horizontally between a pair of adjacent platters and vertically from one pair of platters to a second set. Variants of the IBM 350 were the IBM 355, IBM 7300 and IBM 1405.
Solid-state storage (SSS) is a type of non-volatile computer storage that stores and retrieves digital information using only electronic circuits, without any involvement of moving mechanical parts. This differs fundamentally from the traditional electromechanical storage, which records data using rotating or linearly moving media coated with magnetic material.
Solid-state storage devices typically store data using electrically-programmable non-volatile flash memory, however some devices use battery-backed volatile random-access memory (RAM). Having no moving mechanical parts, solid-state storage is much faster than traditional electro mechanical storage; as a downside, solid-state storage is significantly more expensive and suffers from the write amplification phenomenon.
Solid-state storage devices come in various types, form factors, sizes of storage space, and interfacing options to satisfy application requirements for many different types of computer systems and appliances.
Historically, secondary storage in computer systems has been implemented primarily by using magnetic properties of the surface coatings applied to rotating platters (in hard disk drives and floppy disks) or linearly moving narrow strips of plastic film (in tape drives). Pairing such magnetic media with read/write heads allows data to be written by separately magnetizing small sections of the ferromagnetic coating, and read later by detecting the transitions in magnetization. For the data to be read or written, exact sections of the magnetic media need to pass under the read/write heads that flow closely to the media surface; as a result, reading or writing data imposes delays required for the positioning of magnetic media and heads, with the delays differing depending on the actual technology.
Over time, the performance gap between the central processing units (CPUs) and electro mechanical storage (hard disk drives and their RAID setups) widened, requiring advancements in the secondary storage technology. A solution was found in flash memory, which is an electronic non-volatile computer storage media that can be electrically erased and reprogrammed. Solid-state storage typically uses the NAND type of flash memory, which may be written and read in chunks much smaller than the entire size of the storage device. The size of a minimal chunk (page) for read operations is much smaller than the minimal chunk size (block) for write/erase operations, resulting in an undesirable phenomenon called write amplification that limits the random write performance and write endurance of flash-based solid-state storage devices. Another type of solid-state storage devices uses volatile random-access memory (RAM) combined with a battery that allows the contents of RAM to be preserved for a limited amount of time after the device’s power supply is interrupted. As an advantage, RAM-based solid-state storage is much faster compared to flash, and does not experience write amplification.
As a result of having no moving mechanical parts, solid-state storage virtually eliminates the data access latencies present in electro mechanical storage devices, and allows significantly higher rates of I/O operations per second (IOPS). Additionally, solid-state storage allows much faster sequential access to stored data, consumes less power, has better physical shock resistance, and produces less heat and no vibrations during operation. As a downside, solid-state storage devices have much higher per-megabyte prices than electro mechanical storage devices, and generally come in significantly smaller per-device capacities. Moreover, flash-based devices experience the memory wear that reduces their service life by imposing a limited amount of data that may be written to them, resulting from the limitations of flash memory that impose a finite number of program–erase cycles used to write data. As a result, solid-state storage is frequently used for the creation of hybrid drives, in which solid-state storage serves as a cache for frequently accessed data instead of being a complete substitute for the traditional secondary storage.