In comparison to hard disk drives and similar electromechanical media which use moving parts, SSDs are typically more resistant to physical shock, run silently, and have higher input/output rates and lower latency.[5] SSDs store data in semiconductor cells. As of 2019,[update] cells can contain between 1 and 4 bits of data. SSD storage devices vary in their properties according to the number of bits stored in each cell, with single-bit cells ("Single Level Cells" or "SLC") being generally the most reliable, durable, fast, and expensive type, compared with 2- and 3-bit cells ("Multi-Level Cells/MLC" and "Triple-Level Cells/TLC"), and finally quad-bit cells ("QLC") being used for consumer devices that do not require such extreme properties and are the cheapest per gigabyte (GB) of the four. In addition, 3D XPoint memory (sold by Intel under the Optane brand) stores data by changing the electrical resistance of cells instead of storing electrical charges in cells, and SSDs made from RAM can be used for high speed, when data persistence after power loss is not required, or may use battery power to retain data when its usual power source is unavailable.[6] Hybrid drives or solid-state hybrid drives (SSHDs), such as Intel's Hystor[7] and Apple's Fusion Drive, combine features of SSDs and HDDs in the same unit using both flash memory and spinning magnetic disks in order to improve the performance of frequently-accessed data.[8][9][10] Bcache achieves a similar effect purely in software, using combinations of dedicated regular SSDs and HDDs.
SSDs based on NAND flash will slowly leak charge over time if left for long periods without power. This causes worn-out drives (that have exceeded their endurance rating) to start losing data typically after one year (if stored at 30 C) to two years (at 25 C) in storage; for new drives it takes longer.[11] Therefore, SSDs are not suitable for archival storage. 3D XPoint is a possible exception to this rule; it is a relatively new technology with unknown long-term data-retention characteristics
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The basis for flash-based SSDs, flash memory, was invented by Fujio Masuoka at Toshiba in 1980[38] and commercialized by Toshiba in 1987.[39][40] SanDisk Corporation (then SanDisk) founders Eli Harari and Sanjay Mehrotra, along with Robert D. Norman, saw the potential of flash memory as an alternative to existing hard drives, and filed a patent for a flash-based SSD in 1989.[41] The first commercial flash-based SSD was shipped by SanDisk in 1991.[38] It was a 20 MB SSD in a PCMCIA configuration, and sold OEM for around $1,000 and was used by IBM in a ThinkPad laptop.[42] In 1998, SanDisk introduced SSDs in 2.5-inch and 3.5-inch form factors with PATA interfaces.[43]
In 1995, M-Systems introduced flash-based solid-state drives[45] as HDD replacements for the military and aerospace industries, as well as for other mission-critical applications. These applications require the SSD's ability to withstand extreme shock, vibration, and temperature ranges.[46]
In 1999, BiTMICRO made a number of introductions and announcements about flash-based SSDs, including an 18 GB[47] 3.5-inch SSD.[48] In 2007, Fusion-io announced a PCIe-based Solid state drive with 100,000 input/output operations per second (IOPS) of performance in a single card, with capacities up to 320 GB.[49]
In 2016, Seagate demonstrated 10 GB/s sequential read and write speeds from a 16-lane PCIe 3.0 SSD, and a 60 TB SSD in a 3.5-inch form factor. Samsung also launched to market a 15.36 TB SSD with a price tag of US$10,000 using a SAS interface, using a 2.5-inch form factor but with the thickness of 3.5-inch drives. This was the first time a commercially available SSD had more capacity than the largest currently available HDD.[53][54][55][56][57]
In 2018, both Samsung and Toshiba launched 30.72 TB SSDs using the same 2.5-inch form factor but with 3.5-inch drive thickness using a SAS interface. Nimbus Data announced and reportedly shipped 100 TB drives using a SATA interface, a capacity HDDs are not expected to reach until 2025. Samsung introduced an M.2 NVMe SSD with read speeds of 3.5 GB/s and write speeds of 3.3 GB/s.[58][59][60][61][62][63][64] A new version of the 100 TB SSD was launched in 2020 at a price of US$40,000, with the 50 TB version costing US$12,500.[65][66]
In 2019, Gigabyte Technology demonstrated an 8 TB 16-lane PCIe 4.0 SSD with 15.0 GB/s sequential read and 15.2 GB/s sequential write speeds at Computex 2019. It included a fan, as new, high speed SSDs run at high temperatures.[67] Also in 2019, NVMe M.2 SSDs using the PCIe 4.0 interface were launched. These SSDs have read speeds of up to 5.0 GB/s and write speeds of up to 4.4 GB/s. Due to their high speed operation, these SSDs use large heatsinks and, without sufficient cooling airflow, will typically thermally throttle down after roughly 15 minutes of continuous operation at full speed.[68] Samsung also introduced SSDs capable of 8 GB/s sequential read and write speeds and 1.5 million IOPS, capable of moving data from damaged chips to undamaged chips, to allow the SSD to continue working normally, albeit at a lower capacity.[69][70][71]
Enterprise flash drives (EFDs) are designed for applications requiring high I/O performance (IOPS), reliability, energy efficiency and, more recently, consistent performance. In most cases, an EFD is an SSD with a higher set of specifications, compared with SSDs that would typically be used in notebook computers. The term was first used by EMC in January 2008, to identify SSD manufacturers who would provide products meeting these higher standards.[72] There are no standards bodies who control the definition of EFDs, so any SSD manufacturer may claim to produce EFDs when in fact the product may not meet any particular requirements.[73]
Lower-priced drives usually use quad-level cell (QLC), triple-level cell (TLC) or multi-level cell (MLC) flash memory, which is slower and less reliable than single-level cell (SLC) flash memory.[93][94] This can be mitigated or even reversed by the internal design structure of the SSD, such as interleaving, changes to writing algorithms,[94] and higher over-provisioning (more excess capacity) with which the wear-leveling algorithms can work.[95][96][97]
In 2015, Intel and Micron announced 3D XPoint as a new non-volatile memory technology.[106] Intel released the first 3D XPoint-based drive (branded as Intel Optane SSD) in March 2017 starting with a data center product, Intel Optane SSD DC P4800X Series, and following with the client version, Intel Optane SSD 900P Series, in October 2017. Both products operate faster and with higher endurance than NAND-based SSDs, while the areal density is comparable at 128 gigabits per chip.[107][108][109][110] For the price per bit, 3D XPoint is more expensive than NAND, but cheaper than DRAM.[111][self-published source?]
Another component in higher-performing SSDs is a capacitor or some form of battery, which are necessary to maintain data integrity so the data in the cache can be flushed to the drive when power is lost; some may even hold power long enough to maintain data in the cache until power is resumed.[118][119] In the case of MLC flash memory, a problem called lower page corruption can occur when MLC flash memory loses power while programming an upper page. The result is that data written previously and presumed safe can be corrupted if the memory is not supported by a supercapacitor in the event of a sudden power loss. This problem does not exist with SLC flash memory.[81]
The size and shape of any device are largely driven by the size and shape of the components used to make that device. Traditional HDDs and optical drives are designed around the rotating platter(s) or optical disc along with the spindle motor inside. Since an SSD is made up of various interconnected integrated circuits (ICs) and an interface connector, its shape is no longer limited to the shape of rotating media drives. Some solid-state storage solutions come in a larger chassis that may even be a rack-mount form factor with numerous SSDs inside. They would all connect to a common bus inside the chassis and connect outside the box with a single connector.[6]
For general computer use, the 2.5-inch form factor (typically found in laptops) is the most popular. For desktop computers with 3.5-inch hard disk drive slots, a simple adapter plate can be used to make such a drive fit. Other types of form factors are more common in enterprise applications. An SSD can also be completely integrated in the other circuitry of the device, as in the Apple MacBook Air (starting with the fall 2010 model).[133] As of 2014[update], mSATA and M.2 form factors also gained popularity, primarily in laptops.
Some high performance, high capacity drives uses standard PCI Express add-in card form factor to house additional memory chips, permit the use of higher power levels, and allow the use of a large heat sink. There are also adapter boards that converts other form factors, especially M.2 drives with PCIe interface, into regular add-in cards.
A disk-on-a-module (DOM) is a flash drive with either 40/44-pin Parallel ATA (PATA) or SATA interface, intended to be plugged directly into the motherboard and used as a computer hard disk drive (HDD). DOM devices emulate a traditional hard disk drive, resulting in no need for special drivers or other specific operating system support. DOMs are usually used in embedded systems, which are often deployed in harsh environments where mechanical HDDs would simply fail, or in thin clients because of small size, low power consumption, and silent operation.
Form factors which were more common to memory modules are now being used by SSDs to take advantage of their flexibility in laying out the components. Some of these include PCIe, mini PCIe, mini-DIMM, MO-297, and many more.[137] The SATADIMM from Viking Technology uses an empty DDR3 DIMM slot on the motherboard to provide power to the SSD with a separate SATA connector to provide the data connection back to the computer. The result is an easy-to-install SSD with a capacity equal to drives that typically take a full 2.5-inch drive bay.[138] At least one manufacturer, Innodisk, has produced a drive that sits directly on the SATA connector (SATADOM) on the motherboard without any need for a power cable.[139] Some SSDs are based on the PCIe form factor and connect both the data interface and power through the PCIe connector to the host. These drives can use either direct PCIe flash controllers[140] or a PCIe-to-SATA bridge device which then connects to SATA flash controllers.[141] 2ff7e9595c
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