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Encyclopedia > Solid state drive
A flash SSD in standard 2.5-inch form factor.

A solid state drive (SSD), or solid state disk, is a data storage device that uses solid-state memory to store persistent data. SSD emulates conventional hard disk drive, thus easily replacing it in any application. A flash drive, related to a solid state drive, is a storage device that uses flash memory rather than conventional spinning platters to store data. ... A USB flash drive USB flash drives are NAND-type flash memory data storage devices integrated with a USB (universal serial bus) interface. ... Image File history File linksMetadata E-disk_2-5_scsi. ... Image File history File linksMetadata E-disk_2-5_scsi. ... Many different consumer electronic devices can store data. ... In electronics, solid state circuits are those that do not contain vacuum tubes. ... This article does not cite any references or sources. ... For other uses, see Data (disambiguation). ... This article is about emulation in computer science. ... Typical hard drives of the mid-1990s. ...


With no moving parts, a solid state drive largely eliminates seek time, latency and other electro-mechanical delays and failures associated with a conventional hard disk drive. Moving parts are the components of a device that undergo continuous or frequent motion, most commonly rotation. ... Seek time is one of the several delays associated with reading or writing data on a computers disk drive. ... Latency is a time delay between the moment something is initiated, and the moment one of its effects begins. ...


While SSD is not technically a disk, the term solid state disk emphasises the typical usage as an alternative for a disk drive. In geometry, a disk is the region in a plane contained inside of a circle. ...

Contents

Architecture and function

A high-performance RAM-based SSD.

SSD is commonly comprised of either NAND flash (non-volatile) or SDRAM (volatile). Image File history File links RamSan-400. ... Image File history File links RamSan-400. ... A USB Flash Memory Device Flash memory is a form of EEPROM (Electrically-Erasable Programmable Read-Only Memory) that allows multiple memory locations to be erased or written in one programming operation. ... It has been suggested that this article or section be merged with NVRAM. (Discuss) Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is computer memory that can retain the stored information even when not powered. ... This article or section does not cite any references or sources. ...


SSDs based on volatile memory such as SDRAM are categorized by fast data access, less than 0.01 milliseconds (over 250 times faster than the fastest hard drives in 2004) and are used primarily to accelerate applications that would otherwise be held back by the latency of disk drives. This article or section does not cite any references or sources. ...


DRAM-based SSDs typically incorporate internal battery and backup disk systems to ensure data persistence. If power is lost for whatever reason, the battery would keep the unit powered long enough to copy all data from random access memory (RAM) to backup disk. Upon the restoration of power, data is copied back from backup disk to RAM and the SSD resumes normal operation. Symbols representing a single Cell (top) and Battery (bottom), used in circuit diagrams. ... Random access memory (usually known by its acronym, RAM) is a type of data storage used in computers. ...


However, most SSD manufacturers use nonvolatile flash memory to create more rugged and compact alternatives to DRAM-based SSDs. These flash memory-based SSDs, also known as flash drives, do not require batteries, allowing makers to replicate standard disk drive form factors (1.8-inch, 2.5-inch, and 3.5-inch). In addition, nonvolatility allows flash SSDs to retain memory even during sudden power outages, ensuring data retrievability. Just like DRAM SSDs, flash SSDs are extremely fast since these devices have no moving parts, eliminating seek time, latency and other electro-mechanical delays inherent in conventional disk drives. (Though flash SSDs are significantly slower than DRAM SSDs). A flash drive, related to a solid state drive, is a storage device that uses flash memory rather than conventional spinning platters to store data. ...


Solid state drives are especially useful on a computer which already has the maximum amount of RAM. For example, some x86 architectures have a 4 GB limit, but this can effectively be extended by putting the swap file on a SSD. These SSD do not provide as fast storage as main RAM because of the bandwidth bottleneck of the bus they connect to, but would still provide a performance increase over placing the swap file on a traditional hard disk drive. x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ... This article is about the unit of measurement. ... Virtual memory is intended to help the programmer by taking care of some memory housekeeping duties. ... Design of the Von Neumann architecture For the robotic architecture also named after Von Neumann, see Von Neumann machine The von Neumann architecture is a computer design model that uses a single storage structure to hold both instructions and data. ... In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers and typically is controlled by device driver software. ... Typical hard drives of the mid-1990s. ...

Open casing of 2.5” traditional hard disk drive (left) and solid state drive (center), a drop-in replacement for hard disk drives for mobile computing.

DRAM based SSDs may also work like a buffer cache mechanism. Whenever data is written to memory, the corresponding block in memory is marked as dirty and all dirty blocks can be flushed to the actual hard drive based on the following two strategies: 1. Time (e.g. every 10 seconds, flush all dirty data), 2. Threshold (when the ratio of dirty data to SSD size exceeds some predetermined value, flush the dirty data). Image File history File linksMetadata Size of this preview: 800 × 328 pixel Image in higher resolution (3402 × 1393 pixel, file size: 1. ... Image File history File linksMetadata Size of this preview: 800 × 328 pixel Image in higher resolution (3402 × 1393 pixel, file size: 1. ... For other uses, see cache (disambiguation). ...


Advantages

  • Faster startup - Since no spin-up required.
  • Far faster than conventional disks on random I/O
  • Extremely low read and write latency (seek) times, roughly 15 times faster than the best current mechanical disks.
  • Faster boot and application launch time when hard disk seeks are the limiting factor. See Amdahl's law.
  • In some cases, somewhat longer lifetime - Flash storage typically has a data lifetime on the order of 10 years before degradation. If data is periodically refreshed, it can store data indefinitely. Flash drives have limited endurance (typically, 100,000-300,000 write cycles), which, if a single block is written once per second, leads to failure in a few days at most. However, all flash drives employ a technique known as wear levelling, where writes are smoothly distibuted over all blocks. This means that if one write occurs per second, and n is the number of writes before failure and m is the number of blocks on the disk, failure no longer occurs in n seconds, but in (n*m) seconds. Given that blocks are typically on the order of 1kb and an 8 GB disk will have 8,192 blocks, this gives about 9,500 days before failure; remember also this is with one write per second for that entire time [1]. In consumer level devices you can expect the drive's data storage component to last roughly 10 years in normal use [4]
The disassembled components of a hard disk drive (left) and of the PCB and components of a solid state drive (right).
    • However, it should be noted that certain SCSI hard drives have MTBF of 1.5 million hours (~175 years) and normal SATA harddrives have MTBF of 500,000 hours (~57 years). [5] The actual expected time-to-failure is typically several years, with manufacturers giving warranties of up to and around 5 years in consumer level products [6]. The high MTBFs are not calculated based on expected hard drive time to failure, but rather based on failure rates of hard drives without much wear.
  • Few to no mechanical parts
    • For small drives, lower power consumption and heat production.
    • For small hard drives, no noise - Lack of mechanical parts makes the SSD completely silent (many high-end SSDs include cooling fans).
    • Better mechanical reliability - Lack of mechanical parts results in less wear and tear. High level of ability to endure extreme shock, high altitude, vibration and temperatures[citation needed], which apply to laptops and other mobile devices, or when transported.
  • Security - allowing a very quick "wipe" of all data stored. [citation needed]
  • Relatively deterministic performance [7] - unlike mechanical hard drives, performance of SSDs is almost constant and deterministic across the entire storage. "Seek" time can be constant, and performance does not deteriorate as the media fills up (See: Fragmentation).

However, this is not always the case, as explained below. Flash memory is organised in blocks which can be erased, written or read, but only as whole blocks. The access time is the same for each block. If one or more blocks are used as Access Unit (AU), fragmentation has no harmful effect on access speed. However, for high capacity flash memories the AU would be too big, causing a lot of wasted bytes due to unused space within allocated AU's. Hence, in these cases each block is split up in a number of AU's. Initially AU's will be used sequentially within blocks. So a file with a size of N blocks will use no more than N+2 blocks, the first and last block only partially. However, after some time a situation will occur where no block is available of which all AU's are free, so that one or more extra blocks are needed The result is that said file will need more than N+2 blocks and accessing more blocks takes more time. In the worst case only one AE per block is free and said file will need S*N blocks, where S is the number of AE's per block. The conclusion is that, with bigger flash memory, fragmentation has a detoriating effect on access time. The speedup of a program using multiple processors in parallel computing is limited by the sequential fraction of the program. ... Wear levelling (also written -levelling) is a technique for prolonging the service life of some kinds of eraseable computer storage media, e. ... Image File history File linksMetadata Size of this preview: 800 × 317 pixel Image in higher resolution (2835 × 1122 pixel, file size: 714 KB, MIME type: image/jpeg)(msystems, ) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File linksMetadata Size of this preview: 800 × 317 pixel Image in higher resolution (2835 × 1122 pixel, file size: 714 KB, MIME type: image/jpeg)(msystems, ) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Mean time between failures (MTBF) is the mean (average) time between failures of a system, the reciprocal of the failure rate in the special case when the failure rate is constant. ... For the band, see Laptop (band). ... In computer storage, there are three related uses of the term fragmentation: external fragmentation, internal fragmentation, and data fragmentation, all related to storage. ...

  • For very low-capacity drives, lower weight and size. Size and weight per unit storage are still better for traditional hard drives, and microdrives allow up to 20GB storage in a CompactFlash 42.8×36.4×5 mm (1.7×1.4×.2 in) form factor.

Disadvantages

Flash based SSDs also have several disadvantages:

  • Price - As of early 2007, flash memory prices are still considerably higher per gigabyte than those of comparable conventional hard drives - around US$8 per GB compared to about US$0.25 for mechanical drives.
  • Lower recoverability - After mechanical failure the data is completely lost as the cell is destroyed, while if normal HDD suffers mechanical failure the data is often recoverable using expert help. Subsequent investigations in to this field, however, have found that data can be recovered from SSD memory.
  • Vulnerability to certain types of effects, including abrupt power loss (especially DRAM based SSDs), magnetic fields and electric/static charges compared to normal HDDs (which store the data inside a Faraday cage).
  • Somewhat slower than conventional disks on sequential I/O, the latest perpendicular hard disks doing about 150 MB/s read, with the latest SSDs doing about 120 MB/s read.[2]
  • Limited write cycles. Typical Flash storage will typically wear out after 100,000-300,000 write cycles, while high endurance Flash storage is often marketed with endurance of 1-5 million write cycles (many log files, file allocation tables, and other commonly used parts of the file system exceed this over the lifetime of a computer). Special file systems or firmware designs can mitigate this problem by spreading writes over the entire device, rather than rewriting files in place. [3]
  • Slow random write speeds - as erase blocks on SSDs generally are quite large, they're far slower than conventional disks for random writes [4]

Data recovery is the process of salvaging data from damaged, failed, corrupted or inaccessible primary storage media when it cannot be accessed normally. ... Entrance to a Faraday room A Faraday cage or Faraday shield is an enclosure formed by conducting material, or by a mesh of such material. ...

History of the solid state drive

In the mid 1980s a company named Santa Clara Systems introduced a product named BatRam which consisted of an array of 1 megabit DIP RAM Chips and a custom controller card that emulated a hard drive. The package included a rechargeable battery to preserve the memory chip contents when the power was off. Image File history File links Emblem-important. ... Image File history File links No higher resolution available. ...


msystems introduced flash-based solid state drives in 1995 (SanDisk completed acquisition of msystem in November 2006). Since then, they have been used successfully as hard disk drive replacements by the military and aerospace industries, as well as other mission-critical applications that require the exceptional mean time between failure (MTBF) rates that solid state drives achieve based on their ability to withstand extreme shock, vibration and temperature ranges. SanDisk Corporation (NASDAQ: SNDK), formerly SunDisk, is an American multinational corporation which designs and markets flash memory card products. ...


Commercialization of solid state drives

Cost and capacity considerations

Until recently, solid state disks were too costly for mobile computing. As flash manufacturers transition from NOR flash to single-level cell (SLC) NAND flash and most recently to multi-level cell (MLC) NAND flash to maximize silicon die usage and reduce associated costs, "solid state disks" are now being more accurately renamed "solid state drives" - they have no disks but function as drives - for mobile computing in the enterprise and consumer electronics space. This technology trend is accompanied by an annual 50% decline in raw flash material costs while capacities continue to double at the same rate. As a result, flash-based solid state drives are becoming increasingly popular in markets such as notebook PCs and sub-notebooks for enterprises, Ultra-Mobile PCs (UMPC), and Tablet PCs for the healthcare and consumer electronics sectors. A USB Flash Memory Device Flash memory is a form of EEPROM (Electrically-Erasable Programmable Read-Only Memory) that allows multiple memory locations to be erased or written in one programming operation. ... A USB Flash Memory Device Flash memory is a form of EEPROM (Electrically-Erasable Programmable Read-Only Memory) that allows multiple memory locations to be erased or written in one programming operation. ... The Ultra-Mobile PC (abbreviated UMPC), previously known by its codename Project Origami, is a specification for a small form factor tablet PC. It was developed as a joint development exercise by Microsoft, Intel, and Samsung, among others. ... A Tablet PC is a notebook- or slate-shaped mobile computer. ...


Availability

SSD pioneers such as BiTMICRO Networks and MemTech have marketed solid state disks to the military and industrial markets since the mid-1990s. Afterwards, the enterprise sector also realized the benefits of using SSDs as cache for storage networks and began deploying SSDs in their systems.


SSDs have been appearing in ultra mobile PCs and a few light weight laptop systems, adding a US$ 200 to $800 premium to the systems, depending on the capacity, form factor and transfer speeds. Only a handful of companies offer large (64 GB or larger) SSD drives with write speeds adequate for replacing traditional drives, but these drives are available in limited quantities and are very expensive. Already Sandisk has begun shipping an affordable, fast, energy efficient drive priced at $350 to computer manufacturers. For low-end applications, a USB memory stick may be used as a Flash hard drive for around $10-$100, depending on capacity, or a CompactFlash card may be paired with a CF-to-IDE or CF-to-SATA converter at a similar cost. Either of these requires that write cycle endurance issues be managed, either by not storing frequently written files on the drive, or by using a Flash file system. The United States dollar is the official currency of the United States. ... GB may stand for: // Gordon Brown, the new British Prime Minister George W. Bush, the US President Gb (digraph), a digraph in the Latin alphabet Government and binding, theory by Noam Chomsky Sarin, nerve gas (NATO designation: GB) Gigabit (symbol: Gb or Gbit) Gigabyte (symbol: GB) Game Boy line, a... A 32 MB High Speed CompactFlash Type I card CompactFlash (CF) was originally developed as a type of data storage device used in portable electronic devices. ...

  • BiTMICRO launches flash memory-based solid state disks on January 7, 1999.[5]
  • Mtron announces the fastest flash memory solid state disk, performing 100MB/s Read, 80MB/s Write, 72,000 Max IOPS.[December 2005] [6]
    The Mtron SSD Read: 100MB/s Write: 80MB/s, 76,000 sequential / 16,000 random Max IOPS with less than 0.1ms access time
  • Taiwanese A-DATA introduced at the Las Vegas CES 2007 SSD drives at capacities of 32GB, 64GB (1.8" model) and 128GB (2.5" model).[14] It is expected to be commercially available by mid-2007.[15]
  • SimpleTech has announced a 64GB SSD that is only 9.5mm thick, half the size of competing SSDs. On April 18, 2007 SimpleTech announced 256GB capacity enterprise level drives available immediately and 512GB capacity drives available late 2007.[16][17]
  • Sandisk announces 64GB SSDs of 1.8 UATA 5000 and 2.5 SATA 5000 on June 4, 2007[18]

is the 7th day of the year in the Gregorian calendar. ... This article is about the year. ... Image File history File links Metadata Size of this preview: 800 × 533 pixelsFull resolution (3504 × 2336 pixel, file size: 3. ... Image File history File links Metadata Size of this preview: 800 × 533 pixelsFull resolution (3504 × 2336 pixel, file size: 3. ... HyperDrive (HD) is a series of RAM disks manufactured by HyperOs Systems. ... is the 51st day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... SanDisk Corporation (NASDAQ: SNDK), formerly SunDisk, is an American multinational corporation which designs and markets flash memory card products. ... is the 72nd day of the year (73rd in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... SanDisk Corporation (NASDAQ: SNDK), formerly SunDisk, is an American multinational corporation which designs and markets flash memory card products. ... is the 4th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... Samsung Group is one of the largest South Korean business groupings. ... is the 86th day of the year (87th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... Super Talent Technology is a San Jose, California based designer and manufacturer of DRAM and Flash memory products for the computer industry. ... Dell Inc. ... is the 116th day of the year (117th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... Lexar is an American manufacturer of various digital media and software based in Fremont, CA. Media manufactured by them include SD cards, Memory Sticks, keydrives, and CompactFlash cards. ... Power Quotient International (PQI) is a manufacturer of memory modules and flash memory products, founded in 1997. ... May 28 is the 148th day of the year (149th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... This article is about the history, geography, and people of the island known as Taiwan. ... Vegas redirects here. ... The International Consumer Electronics Show (CES) is a trade show held each January in Las Vegas, Nevada, and is sponsored by the Consumer Electronics Association. ... SimpleTech, Inc. ... SanDisk Corporation (NASDAQ: SNDK), formerly SunDisk, is an American multinational corporation which designs and markets flash memory card products. ... June 4 is the 155th day of the year (156th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ...

See also

A RAM-Disk, Ramdisk or Ramdrive is a virtual solid state disk that uses a segment of active computer memory, RAM, as secondary storage, a role typically filled by hard drives. ... This article does not cite any references or sources. ... Disk Drive is the afternoon show on CBC Radio Two. ... A flash drive, related to a solid state drive, is a storage device that uses flash memory rather than conventional spinning platters to store data. ... This article refers to the computer hard disk. ... It has been suggested that this article or section be merged with NVRAM. (Discuss) Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, is computer memory that can retain the stored information even when not powered. ... Random access memory (usually known by its acronym, RAM) is a type of data storage used in computers. ... Semiconductor memory is a generic term referring to any computer storage method implemented on a semiconductor-based integrated circuit. ... A USB flash drive USB flash drives are NAND-type flash memory data storage devices integrated with a USB (universal serial bus) interface. ... Volatile memory refers to computer memory that must be powered to maintain its data. ...

External references

References

  1. ^ SSD Myths and Legends
  2. ^ http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=9033699
  3. ^ http://lwn.net/Articles/234441/
  4. ^ http://www.storagesearch.com/easyco-flashperformance-art.pdf
  5. ^ BiT Microsystems Debuts FlashDrive Record-Breaking All-Electronic Disk
  6. ^ [1]
  7. ^ [2]
  8. ^ Adtron press release February 20, 2007
  9. ^ Samsung 64GB Launch
  10. ^ Super Talent readies 128GB flash drive, 4GB DIMMs
  11. ^ Dell Gets Flash With SSD Option for Laptops
  12. ^ [3]
  13. ^ As The Forefather of Industrial SSDs, PQI Sets New Standards with New High Speed and Large Capacity Industrial CF and SSD
  14. ^ Future of Flash revealed
  15. ^ A-DATA exposes 128GB SSD to the camera
  16. ^ SimpleTech accounces world's thinnest 2.5 inch 64GB SSD
  17. ^ SimpleTech announces 512GB and 256GB 3.5-inch SSD drives
  18. ^ SanDisk Launches 64 Gigabyte Solid State Drives for Notebook PCs, Meeting Needs for Higher Capacity

 
 

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