Flash storage: A cheat sheet


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With over a dozen kind components, realizing what the perfect flash reminiscence card and SSD expertise is obtainable may be daunting.

CES 2019: New storage improvements in SD, SSD, and HDDs improve pace and density
At CES 2019, makers of moveable flash reminiscence playing cards, in addition to strong state and conventional platter laborious drives launched new merchandise benefiting enterprise customers and digital professionals.

Flash reminiscence is an digital, non-volatile information storage medium that’s erased and reprogrammed electrically. It’s the foundation of quite a lot of storage merchandise for differing use circumstances, kind components, and pace or efficiency necessities. Flash reminiscence is the underpinning of recent shopper expertise—it’s used to retailer images taken with digital cameras, and is present in smartphones, tablets, sport consoles, in addition to solid-state drives utilized in computer systems.

TechRepublic’s flash storage cheat sheet is an summary of the important thing info you’ll want to know concerning the subject. This text will probably be up to date when new codecs and post-flash applied sciences are launched.

SEE: All of TechRepublic’s cheat sheets and sensible particular person’s guides

What’s flash storage?

Flash reminiscence is an digital, solid-state storage medium developed by Fujio Masuoka whereas working at Toshiba, circa 1980. Masuoka first publicly demonstrated the invention in 1987, with Intel producing the primary industrial flash chip in 1988.

Masuoka’s invention covers two associated varieties of non-volatile reminiscence: NOR and NAND. NOR flash takes longer to put in writing or erase, however offers byte-level random entry, making it an appropriate substitute for read-only reminiscence (ROM) chips. NAND flash offers sooner write and erase instances, in addition to extra dense storage capabilities. NAND flash is written and skim at a block degree, making it unsuitable for embedded use circumstances that require byte-level entry.

Usually, NOR flash is restricted to mission-critical purposes and embedded use circumstances such because the firmware of a pc or an embedded digital gadget. Flash reminiscence playing cards and solid-state drives (SSDs) make the most of NAND flash for mass storage.

What are the drawbacks of flash storage?

Flash storage has a finite lifespan by way of the variety of instances a block may be erased and rewritten. As NAND flash reminiscence turns into extra dense by way of using multi-level cell expertise, this lifespan has decreased sharply.

SLC NAND, for instance, presents comparatively low capacities, although it may face up to roughly 100,000 write/erases per block. MLC NAND (two-bit) presents 1,000 to three,000 cycles in high-capacity purposes and 5,000 to 10,000 cycles in medium-capacity purposes, whereas TLC NAND (three-bit) presents roughly 1,000 cycles.

3D NAND presents larger write/erase cycles, with 3D MLC NAND rated between 6,000 to 40,000 cycles, 3D TLC NAND rated between 1,000 to three,000 cycles, and 3D QLC NAND (four-bit) rated from 100 to 1,000 cycles.

Producers measure the lifespan of SSDs by way of “complete bytes written,” or TBW. A 2 TB Intel 660p SSD, which makes use of 3D QLC NAND, is rated for 400 TB. In distinction, a 2 TB Intel 760p SSD, which makes use of 3D TLC NAND, is rated for 1152 TB.

Virtually talking, there isn’t a restrict to the variety of instances a block may be learn.

How is flash storage totally different from a solid-state drive (SSD)?

SSDs make the most of NAND flash expertise for mass storage, although this isn’t the one element utilized in an SSD. Sometimes, SSDs are comprised of a disk controller, a DRAM cache, and NAND flash. The disk controller is used to handle the environment friendly use of NAND, resembling stopping uneven put on ranges of flash cells, extending the lifespan of a drive.

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What moveable flash storage kind components exist?

Completely different kind components of flash storage playing cards exist to accommodate the number of units that the playing cards are used with. Whereas most consumer-level units now focus on Safe Digital (SD), prosumer units require larger speeds than SD is instantly capable of present.

Safe Digital (SD)

Safe Digital (SD) is the trade customary flash reminiscence card; it was launched in 1999, and it’s utilized in virtually each class of shopper digital units since its inception.

The unique format, Safe Digital Normal Capability (SDSC), was nominally restricted to 2 GB. In 2006, the Safe Digital Excessive Capability (SDHC) format was launched to permit for playing cards as much as 32 GB. The Safe Digital eXtended Capability (SDXC) format was launched in 2009 to permit for playing cards as much as 2 TB. In June 2018, the Safe Digital Extremely Capability (SDUC) format was launched to permit for playing cards better than 2 TB; the specification permits playing cards as much as 128 TB.

Presently, the most important commercially obtainable SD card is 1 TB.

Units that assist SD playing cards are primarily backward appropriate, with some restricted ahead compatibility. Units that declare solely assist for SDHC are sometimes ready to make use of bigger SDXC playing cards by reformatting the cardboard (utilizing a pc) to make use of the FAT32 file system. For a tool to be offered with a SDXC or a SDUC brand, it should assist the patent-encumbered exFAT file system.

With a purpose to accommodate the shrinking sizes of shopper electronics, smaller variants of SD playing cards had been developed. The miniSD customary was launched in 2003, although loved solely restricted assist earlier than being discontinued after about 5 years.

microSD, previously known as TransFlash, was launched in 2005. microSD playing cards are generally present in Android smartphones and tablets, sport methods just like the Nintendo Swap, and single-board computer systems (SBCs) just like the Raspberry Pi. microSD playing cards can be utilized in legacy units that assist solely miniSD or full-size SD playing cards utilizing passive adapters.

CompactFlash (CF)

CompactFlash was launched in 1994 and is designed as a 50-pin subset of the 68-pin PCMCIA customary. Regardless of the age of the usual, it’s nonetheless used on skilled DSLR cameras from Canon and Nikon.

The biggest capability at present obtainable is 512 GB.

When it comes to signaling, CompactFlash is much like ATA laborious disks. This was leveraged by the IBM Microdrive, which carried out a miniature laborious disk on the CompactFlash interface, with capacities as much as eight GB. Microdrive and comparable rivals have lengthy since been discontinued.


CFexpress, introduced in September 2016, is the successor to CompactFlash. It’s used solely in professional-grade cameras. CFexpress relies on the PCI Specific three.zero interface, and leverages NVM Specific to offer low latency and processing overhead. 1 TB CFexpress playing cards had been previewed at CES 2019 and are anticipated to be obtainable in retail channels this 12 months.

Model 1.zero of the specification offers a PCIe three.zero x2 connection for CFexpress playing cards, for a most pace of 1.96 GB/s.

Although the specification permits totally different kind components, CFexpress playing cards inherit the XQD kind issue, which was developed by Sony, Nikon, and SanDisk, although the latter declined to truly produce any XQD playing cards. Due to IP licensing encumbrances, XQD playing cards not produced by Sony had been restricted, in flip limiting widespread adoption. Sony has pledged to fabricate CFexpress playing cards, creating an trade consensus round CFexpress.

Common Flash Storage (UFS) card

The united statescard customary was printed in March 2016, and was meant to interchange microSD playing cards. Although the usual was up to date in January 2018, no UFS playing cards are commercially obtainable, and as of March 2019, no units are marketed as supporting interoperability with the format.

USB flash drives

USB flash drives embody all kinds of comparable merchandise. On the decrease finish, these drives sometimes embrace a easy controller for wear-leveling and USB connectivity; higher-end USB flash drives embrace DRAM for write caching. Sometimes, these drives can be found within the “gumstick” kind issue, with the USB port hooked up to the drive, resulting in popularly being known as USB sticks.

Early USB flash drives sometimes included a write-protect change. This characteristic has been relegated to the specialty market, although producers resembling Kanguru produce USB three.zero flash drives with write-protect switches.

Drives with bigger capacities do exist, such because the Samsung T5 SSD, which requires using an exterior cable to hook up with a pc. The Samsung T5 SSD is technically a USB-connected moveable SSD that mixes an mSATA SSD with a SATA to USB3 bridge in a rugged enclosure.

Legacy kind components

SmartMedia playing cards had been a Toshiba format launched in 1995 and used for digital cameras and to a lesser extent in PDAs and MP3 gamers. The biggest SmartMedia card was 128 MB and was produced in (older) 5V and (newer) three.3V variants. The digital digital camera trade transitioned away from SmartMedia in 2003.

xD-Image Playing cards had been utilized in Fujifilm and Olympus digital cameras from 2002 to 2009, in capacities from 16 MB to 2 GB. xD and SmartMedia playing cards are functionally uncooked NAND flash chips with none disk controller.

Reminiscence Stick was a flash reminiscence format developed by Sony in 1998. Although it was licensed to different corporations, Reminiscence Stick was restricted primarily to Sony electronics from 1998 to 2012. Sony made the vast majority of Reminiscence Stick merchandise, although the format was additionally produced by SanDisk and Lexar. Seven Reminiscence Stick kind components had been launched, with capacities from 128 MB to 32 GB. The PlayStation Vita used a proprietary Reminiscence Stick kind issue, produced solely by Sony. The PlayStation Vita was discontinued in March 2019.

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What solid-state drive (SSD) kind components exist?

In comparison with a conventional platter laborious drive—which requires using a drive head to be moved by an actuator throughout a platter to learn and write information—NAND flash storage has no transferring components, making these solid-state drives.

Stable-state drives utilized in laptops, desktops, and servers had been initially engineered as drop-in replacements for conventional laborious drives; because of this, early SSDs are considerably shoehorned to work in present requirements.

2.5″ SATA drives

Early consumer-facing solid-state drives most frequently took the type of 2.5″ disk drives, the identical kind issue utilized in small kind issue (SFF) PCs and pocket book computer systems, related over SATA. Due to the restrictions of SATA and AHCI, the utmost pace a SATA-linked drive can obtain is roughly 550 MB/sec.

Early 2.5″ drives generally crammed your complete 2.5″ area internally and used the usual 9.5mm peak of conventional drives. Newer SATA drives, just like the Essential MX500, use solely a part of the two.5″ area internally and have a 7mm enclosure, with a spacer included to be used in units (sometimes, notebooks) that require the additional 2.5mm to be crammed.

SSDs in a three.5″ kind issue are exceedingly uncommon. The OCZ Colossus LT in 2010 utilized the additional area to achieve 1 TB, at a premium worth of $four,000. Newer three.5″ SSDs just like the Nimbus Knowledge 100 TB ExaDrive are constructed solely for enterprise purposes.


Notebooks and SFF PCs had been typically constructed with assist for mSATA playing cards, which offer the identical signaling as 2.5″ SATA drives in a 30 x 50.95 mm bundle. Pc producers largely deserted the format in 2015 in favor of M.2 drives.

Samsung continued to assist the format into early 2018 with the 860 EVO, the final Samsung SSD to be launched for the shape issue, in capacities as much as 1 TB.


M.2, previously Subsequent-Era Kind Issue (NGFF), is a flexible kind issue used for high-performance SSDs, in addition to different peripherals together with Wi-Fi and Bluetooth networking playing cards, WWAN (4G LTE, 5G modems), and different units. M.2 SSDs can use legacy SATA connections or PCI Specific with AHCI or NVMe.

M.2 SSDs are 22 mm large and can be found in lengths of 30, 42, 60, 80, and 110 mm—42 and 80 mm are the commonest. Sizes are sometimes denoted within the format M.2-WWLL resembling M.2-2280.

M.2 is changing into the trade default for SSDs and are used extensively in pocket book and SFF PCs. On desktops, fanatic PC motherboards sometimes embrace a number of M.2 PCIe x4 slots.

Presently, the most important capability M.2-2280 SSD is 2 TB.

NGSFF, previously NF1, is a hot-swappable model of M.2 devised by Samsung and meant for information facilities that require the power to swap SSDs on operating methods.


U.2, previously SFF-8639, is technically an interface—primarily, it offers the PCIe x4 lane of M.2 for a similar bodily kind issue as SATA drives. In idea, it might even be doable to make use of the interface for three.5″ drives.

PCI Specific drives

SSDs that plug instantly into PCIe slots on motherboards exist, although the format has fallen into disuse. By late 2010, mainstream shopper SSDs had been bottlenecked by the comparatively restricted throughput granted by SATA, prompting early PCI Specific drives to be produced. These drives used AHCI fairly than NVMe, offering larger potential learn/write speeds however not appreciably higher efficiency by way of random I/O.

SEE: Catastrophe restoration and enterprise continuity plan (Tech Professional Analysis)

Enterprise-targeted PCI Specific drives exist, such because the Intel SSD DC P3608, although this drive has since been discontinued. Intel continues to supply the mid-2015 SSD 750 sequence as PCI Specific playing cards, although these are slower than newer M.2 choices.

For a single drive, PCI Specific to M.2 adapter boards are available. When it comes to electrical signaling, M.2 offers a full PCIe x4 connection, making the conversion primarily passive—no efficiency loss is incurred by way of using an adapter. Some producers supply these adapters with their SSDs typically at a nominal extra value. PCIe to M.2 adapters are producer agnostic—an aftermarket adapter can be utilized for any PCIe M.2 drive.

Disk-on-Module (DOM)

DOM SSDs are meant to interchange Parallel ATA (PATA) disks utilized in legacy gear. Manufacturing of PATA HDDs ended greater than a decade in the past, and continued reliance on these disks invitations the potential for information loss. DOM SSDs plug instantly right into a PATA port, permitting airflow obstructing IDE cables to be eliminated.

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How can I inform if a flash storage card or SSD is quick sufficient for my use case?

Completely different requirements and pace lessons exist for various flash reminiscence playing cards, although the variety of differing ranking methods for various use circumstances can develop into complicated.

Bus interface requirements for SD playing cards

The bus interface customary determines how an SD card connects to a number gadget, giving a peak potential efficiency, however it’s not indicative of how particular person playing cards carry out. Previous to the introduction of Extremely Excessive Velocity (UHS) lessons, SD playing cards had been restricted to both 12.5 MB/s or 25 MB/s, although no standardized marking exists to point the distinction.

  • UHS-I presents 50 MB/s in half- or full-duplex mode, or 104 MB/s in half-duplex mode.
  • UHS-II presents 156 MB/s in full-duplex mode, or 312 MB/s in half-duplex mode.
  • UHS-III presents 312 MB/s or 624 MB/s in full-duplex mode. It has no half-duplex mode.

SD Specific (additionally marked SD-Specific I) presents 985 MB/s as a PCIe three.zero x1 lane, with NVMe assist.

Per specs, UHS and SD Specific playing cards should be backward-compatible, although the utmost pace doable is decided by the ranking of the host gadget.

Velocity class rankings for SD playing cards

Overlapping and conflicting requirements for SD playing cards for various use circumstances typically causes confusion when deciding on an SD card. Here is what the totally different pace class rankings imply in real-world phrases.

Min. sequential write pace Velocity Class UHS Velocity Class Video Velocity Class
2 MB/s Class 2 (C2)
four MB/s Class four (C4)
6 MB/s Class 6 (C6) Class 6 (V6)
10 MB/s Class 10 (C10) Class 1 (U1) Class 10 (V10)
30 MB/s Class three (U3) Class 30 (V30)
60 MB/s Class 60 (V60)
90 MB/s Class 90 (V90)

Nominally, capturing video in 4K requires at the least a V6-rated card, whereas 8K requires a V30-rated card. Necessities fluctuate between units.

Utility Efficiency Class primarily measures IOPS, with the intent of offering a typical for operating apps from smartphones.

Class Min. random learn Min. random write Min. sequential write pace
A1 1500 IOPS 500 IOPS 10 MB/s
A2 4000 IOPS 2000 IOPS 10 MB/s

Velocity rankings for SSDs

With using DRAM caches, it’s doable for SSDs, notably SATA SSDs, to saturate the obtainable bandwidth of the bus they’re related to. These pace rankings are helpful just for sequential learn/write, as different components defined within the part beneath affect how SSDs deal with bulk operations.

Connection kind Max. pace Working state
SATA 2.x (three Gb/s) 300 MB/s Legacy
SATA three.x (6 Gb/s) 600 MB/s Present
PCIe three.zero x1 985 MB/s Present
PCIe three.zero x2 1970 MB/s Present
PCIe three.zero x4 3940 MB/s Present

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How do I choose the perfect flash storage for my gadget?

Partially, that is subjective. If you wish to carry a FLAC-encoded music assortment in your smartphone, a bigger card with slower write speeds is satisfactory to your use case. For operating purposes saved on a flash card, or to be used in a sport system just like the Nintendo Swap, an A2-rated card would theoretically present larger efficiency.

Buying a real, name-brand product is vital. For SD playing cards, off-brand or knockoff merchandise offered by disreputable sellers incorrectly report their dimension. In follow, this implies a card presupposed to be 128 GB might solely have 16 GB storage. A tool might write past that 16 GB capability, however newly-written information can be misplaced or overwrite present information.

For SSDs, think about the variety of writes wanted for a job. QLC SSDs supply the next storage capability however can solely endure a restricted variety of writes. PCIe SSDs are at all times larger efficiency than SATA SSDs. For desktops, at all times use an M.2 or M.2 to PCIe bridge to your SSD, when you have PCIe connections obtainable. For laptops, units with M.2 capabilities sometimes ship with a M.2 drive built-in, limiting upgradability choices.

It’s doable to buy SSDs at a storage capability equal to that of conventional platter-based laborious disk drives, although the associated fee per gigabyte is considerably larger—presently, a 15.36 TB Seagate Nytro SSD is over $6,000, although a 14 TB Seagate IronWolf Professional is $570. This impact is magnified when constructing enterprise storage arrays. In lots of use circumstances, all-flash arrays are inefficient from a value perspective, although tiered storage options might add pointless complexity.

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Picture: Henning Marquardt, Getty Pictures/iStockphoto

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