Nobody has ever complained about a memory card being too fast and, increasingly, electronics manufacturers are expecting you to have high-speed memory cards that are compatible with certain features. These days, smartphones, tablets, and even laptops often rely on memory cards to expand their storage. With consumers demanding higher resolution and less compressed video from cameras, manufacturers have responded by supplying memory cards that are not only more durable, but more capable. Today, cameras are recording 4K video to microSD cards and raw HD video to SD cards. Luckily, memory cards have kept up with the rising demand, and the fastest cards around rival SSD drives, though finding out which ones are truly fast can be a challenge.
Determining Card Speed and the Dreaded “Up To”
When memory card manufacturers list their cards’ read and write speeds, they often use terms like “up to” or “maximum” when reporting the spec. A maximum read speed or speed “up to” a certain amount is the maximum burst speed of a card. It might be able to sustain that speed for a few seconds, which is great for saving a picture quickly, such as when shooting Sony’s Alpha a9 or Alpha a9 II at their maximum burst rate of 20 frames per second, but don’t expect to see read and write speeds like that for sustained transfers, such as when you’re shooting video. Plus, some manufacturers are a bit more liberal with the speeds they quote than others. Sustained transfer speeds can vary greatly from card to card, so to determine a memory card's overall speed—just looking at the card's advertised maximum speed isn’t always the best yardstick.
It is also important not to confuse bits and bytes. Bits are abbreviated with a lowercase b (as in Mb/s), while bytes are abbreviated with a capital B (MB/s). There are eight bits in one byte. Often, video-recording codecs will list their speeds in bits per second, while cards list their speeds in bytes per second. So, when a video camera like the GH5 records at 400 Mb/s, remember that is “only” 50 MB/s.
Luckily, memory cards have several metrics to help you sort out which ones are fast all around. To the uninitiated, they can be a bit overwhelming and look like random numbers, so in this article we will not only reveal what the fastest cards are, but also help you understand why.
SD and microSD Cards: SD versus SDHC versus SDXC
One of the more obvious metrics to consider when comparing SD cards is whether they are SD, SDHC, or SDXC cards. While these cards look the same, the file format they use is different, which determines the maximum capacity of the card. Plain SD cards have a maximum capacity of 2GB, while SDHC cards max out at 32GB, and SDXC cards can support up to 2TB—though the largest cards are currently at 1TB. This metric does not affect speed at all; an SDHC card can be just as fast as a SDXC card, and often, they are.
UHS (Ultra High Speed) Card Classifications
Some SD cards have UHS (Ultra High Speed) Classifications. A UHS (Ultra High Speed) Classification commutates a card’s bus speed, or the maximum speed at which a memory card is capable of transferring data at. But, just like plugging a slow hard drive into a 40 Gb/s Thunderbolt 3 port won’t magically speed it up, a UHS classification doesn’t affect the speed of the memory in the card, but manufacturers will rarely make a UHS-I card that is unable to read or write faster than a non-UHS card. Non-UHS SD cards max out at 25 MB/s, but UHS cards can work much faster. Currently, there are two types of UHS classifications: UHS-I Cards, which have a maximum theoretical speed of 104 MB/s, and UHS-II cards that allow for a maximum transfer speed of 312 MB/s. UHS-II cards also have a second row of electrical contacts to aid in the speed boost. If your memory card reader or camera does not have the second row of contacts, the speed will be more in line with UHS-I cards. A card’s UHS classification is a good way to help gauge a card’s burst speeds.
Sustained Speed Class Ratings
Since card manufacturers almost always only give you burst read and write speeds instead of sustained speeds, it can be difficult to pick out a card for other uses than burst photography. Many new 4K-capable cameras write at very high bit rates, and if you plan on recording video for longer than a few seconds, the burst speed doesn’t help much. Also, there can be a huge variation between the maximum burst read speeds and the minimum sustained write speeds of different cards. It’s not a simple ratio. To determine the minimum write speed of a card, you need to look at its speed class rating. A speed class rating means that the card has been verified to never write slower than its class rating. Since there are different speed classes, some cards will write faster than others, but you can be comfortable knowing that any card with a speed class rating will never write slower than that speed. Some popular speed class ratings used on SD cards today are:
- V90: Minimum 90 MB/s Sustained Write Speed
- V60: Minimum 60 MB/s Sustained Write Speed
- V30: Minimum 30 MB/s Sustained Write Speed
- U3: Minimum 30 MB/s Sustained Write Speed
- V10: Minimum 10 MB/s Sustained Write Speed
- U1: Minimum 10 MB/s Sustained Write Speed
- Class 10: Minimum 10 MB/s Sustained Write Speed
- V6: Minimum 6 MB/s Sustained Write Speed
- Class 6: Minimum 6 MB/s Sustained Write Speed
- Class 4: Minimum 4 MB/s Sustained Write Speed
Random Speed Class Ratings
Many smartphone and tablet manufacturers include microSD card slots for users to expand their storage space. Installing applications and other small data files stresses out memory cards in a completely different way than video and photo typically do, because it often requires reading many small files simultaneously, rather than one single extremely large file. Simply measuring sequential read and write speeds doesn’t do this justice, which is why the SD card association introduced a new type of speed class—the Application Performance Class. Unlike the other speed classes, the Application Performance Class measures random read and write speeds, typically shown in IOPS. Also, since smartphones and tablets almost exclusively use microSD cards for storage space, only microSD cards are certified for Application Performance Class—even though there is no technical reason full-size SD cards can’t be certified, as well. The following is a breakdown of popular Application Performance Classes.
- A1: Minimum 1500 IOPS (about 11 MB/s) random read speed and minimum 500 IOPS (about 4 MB/s) random write speed
- A2: Minimum 4000 IOPS (about 31 MB/s) random read speed and minimum 2000 IOPS (about 15 MB/s) random write speed
The Fastest SD Cards
Now that we’ve decoded all the technical jargon, it should be clear that if you want the fastest SD cards you can get, look for UHS-II cards with a V90 rating. Luckily, B&H carries many UHS-II / V90 cards from a few manufacturers. Sony SF-G Tough Series UHS-II Memory Cards are available in 32GB, 64GB, and 128GB capacities, and offer read speeds up to 300 MB/s and write speeds up to 299 MB/s, which should satisfy the most bandwidth-hungry cameras. Delkin Devices Power Cards are available in 128GB, 64GB, and 32GB capacities, and offer read speeds up to 300 MB/s and write speeds up to 250 MB/s. AngelBird offers 256GB, 128GB, and 64GB UHS-II cards with a read speed of 300 MB/s and a write speed of 260 MB/s, while ProGrade Digital makes UHS-II cards with a read speed of 250 MB/s and a write speed of 200 MB/s.
If you don’t need 60 MB/s sustained write speeds but still want to benefit from high burst speeds, thanks to UHS-II, SanDisk’s 128GB Extreme PRO UHS-II microSDXC card offers read speeds up to 275 MB/s and write speeds up to 100 MB/s. These cards offer read speeds of up to 300 MB/s and write speeds of up to 260 MB/s, though they are only U3 rated, meaning their sustained write speeds likely will drop off faster than V90 cards.
Does your camera only support UHS-I speeds? If so, there’s not much point in paying more for UHS-II media, since it would just default to the read and write speeds of your camera. So, if you rely on UHS-I cards, SanDisk makes Extreme PRO UHS-I media with respectable read speeds of up to 170 MB/s and write speeds of up to 90 MB/s.
The Fastest microSD Cards for Cameras
microSD cards are essentially miniaturized SD cards, and share the same UHS and speed class properties as their full-sized brethren; so just like full size SD cards, the fastest microSD cards are UHS-II / V90, which are currently made by Delkin Devices and Lexar. Delkin’s Power UHS-II microSD series offers a 32GB and 64GB cards with a maximum read speed of 300 MB/s and a maximum write speed of 250 MB/s, while Lexar’s Professional 1800x UHS-II microSDXC cards go up to 270 MB/s reads and 150 MB/s writes. Delkin’s Prime UHS-II microSDXC cards are V60 rated, with read speeds of up to 300 MB/s and write speeds of up to 100 MB/s. If you don’t need 60 MB/s sustained write speeds but still want to benefit from high burst speeds, thanks to UHS-II, SanDisk’s 128GB Extreme PRO UHS-II microSDXC card offers read speeds up to 275 MB/s and write speeds up to 100 MB/s.
However, many microSD-compatible devices don’t have UHS-II capable card readers able to take advantage of the fast speeds offered by UHS-II. If that’s the case, UHS-I / U3-rated cards are also worth a look. Delkin Devices offers Advantage UHS-I microSD cards in capacities of 32GB, 64GB, and 128GB. These cards offer up to 100 MB/s read speeds and 75 MB/s write speeds. SanDisks’s fastest UHS-I microSD cards are the U3-rated Extreme PLUS line, which offer maximum read speeds of 100 MB/s and maximum write speeds of 90 MB/s, and are available in capacities of 32GB, 64GB, and 128GB. Additional UHS-I microSD memory cards are available from Sony, Transcend, and PNY.
The Fastest microSD Cards for Smartphones and Tablets
Users looking to use microSD cards to increase the storage capacity of their mobile devices could benefit from looking at a slightly different family of memory cards. While cards designed for extremely fast sequential read and write speeds tend to be fast all around, there is little need for a UHS-II bus when you are mostly reading and writing lots of small files, which is why Application Performance Class cards are recommended. The fastest, and only A2-certified microSD card family available right now are SanDisk Extreme cards. Available in capacities as large as 1TB, these UHS-I cards are A2 certified, meaning they offer minimum random read speeds of at least 4000 IOPS (about 31 MB/s), minimum random write speeds of at least 2000 IOPS (about 15 MB/s), and minimum sustained write speeds of at least 10 MB/s, which should translate to respectable performance when being used as local storage. These cards are also suitable for use beyond mobile devices, as they are V30 rated and feature max read speeds of 160 MB/s, max write speeds of 90 MB/s and minimum write speeds of 30 MB/s.
CompactFlash cards used to be the faster and more professional big brother of SD cards; however, several years ago, the CompactFlash Association announced there would be no more updates to the format, leaving card performance with a glass ceiling. Today, CompactFlash cards have hit their performance ceiling, and are about half the speed of the fastest SD cards. The UDMA 7 interface has a maximum possible transfer speed of 167 MB/s, and even if a card manufacturer put faster flash memory in a UDMA 7 card, it wouldn’t matter—it would be like plugging an SSD drive into a USB 2.0 port on your computer (well, not quite that bad, but you get the point). The bright side of this is that the sustained transfer speeds of CompactFlash cards are often a lot closer to the maximum speed; however, since there are no official speed classes for CompactFlash cards you must trust the manufacturer’s advertised speeds.
CompactFlash Card Speed Class Ratings
Many CompactFlash cards have speed ratings like 400x, 800x, 1066x, etc. This speed rating system is quite old and is based on the data-transfer rate of audio CD files, a paltry 150 KB/s. Needless to say, this doesn’t have much bearing on anything you will probably be doing with your cards, so while you could figure out how fast an 800x card is in KB/s by multiplying 150 by 800 and converting KB/s to MB/s by dividing by 1,000 (the answer is 120 MB/s), you could also just go by a card’s stated 120 MB/s speed.
The Fastest CompactFlash Cards
Because the maximum speed of CompactFlash cards has been capped at 167 MB/s, almost all card manufacturers now offer cards capable of peak read and write performance at that speed. The fastest cards will be UDMA 7 and advertised as having maximum read speeds between 160-165 MB/s. Lexar’s fastest line of CompactFlash cards is the Lexar Professional 1066x, available in capacities from 32GB to 256GB. These cards have a 160 MB/s maximum write speed, a maximum write speed of 155 MB/s, and a minimum write speed of 65 MB/s. SanDisk’s Extreme Pro line of cards also offers similar performance of up to 160 MB/s read and 150 MB/s write speeds, while the Transcend Ultimate and Delkin Devices Cinema CompactFlash card lines also offer similar maximum read speeds at 160 MB/s, though their write speeds, at maximum of 120 MB/s, are a bit slower than the Lexar and SanDisk cards. These cards are as fast as CompactFlash cards are going to get—if you want something faster, you will need a different type of memory card.
Newer Memory Card Types: XQD Cards
XQD Cards are the reason CompactFlash cards aren’t getting a speed update, since they are the CompactFlash Association’s official replacement for CompactFlash cards. XQD cards are based on the PCIe standard (with an 8 Gb/s bus speed), offer far higher maximum transfer speeds than CompactFlash, are much smaller, and have a more rugged build than SD cards. There are currently two versions of XQD cards, Version 1.0, which allows for maximum transfer rates of 500 MB/s, and Version 2.0, which allows for speeds up to 1000 MB/s. While still limited in use, both versions offer faster possible transfer rates than CompactFlash.
The Fastest XQD Cards
While Sony is no longer the only XQD memory card manufacturer, its XQD G Series cards are the fastest ones around. Available in capacities of 32GB, 64GB,120GB, and 240GB, they are XQD 2.0 compliant and offer read speeds up to 440 MB/s and write speeds up to 400 MB/s. Delkin Devices also makes Premium XQD cards in capacities of 64GB, 120GB, and 240GB with performance similar to Sony’s cards. When it comes to speed, these cards give SATA SSD drives a run for their memory.
CFast 2.0 Cards
Even though CFast cards look almost identical to CompactFlash cards, they are a completely different standard, and will not work in CompactFlash card slots or devices. They are not backed by the CompactFlash association, but are beginning to pick up some steam due to the slow adoption of XQD cards. CFast Cards use SATA I (1.5 Gb/s) connectors to interface with computers and cameras, and the new CFast 2.0 cards use SATA III, meaning they allow for the same maximum transfer rate of 6 Gb/s (750 MB/s) as SATA III drives. While the interface isn’t quite as fast as XQD 2.0, there still aren’t any cards in either format that come close to the maximum possible speed so, at this point it really isn’t an issue.
The Fastest CFast 2.0 Cards
Currently, SanDisk, Delkin Devices, Transcend, Hoodman, ProGrade Digital, and Lexar offer CFast 2.0 cards. These cards are available in capacities ranging from 64GB to 512GB and all feature fast read and write speeds, with the fastest read speeds of 560 MB/s belonging to the cards from Delkin Devices and Hoodman, while the fastest write speed of 495 MB/s belongs to Delkin Devices’ CFast 2.0 card. The other cards mentioned here aren’t slow, by any means, and offer read speeds ranging from 510-550 MB/s and write speeds ranging from 370-455 MB/s.
Future Memory Card Types – UHS-III, SD Express, and CFexpress
While UHS-II SD cards offer the fastest speeds of their respective camp that are available right now, their replacement has been announced and should show up sometime in the future. In the case of XQD 2.0 cards, not only has their replacement been announced, it is already starting to hit the market.
UHS-III memory cards, offering bus speeds up to 624 MB/s, were announced in February of 2017 and never really appeared, and in June 2018, even faster SD Express cards were announced. SD Express cards use the PCIe standard for bus transfer speeds of up to 985 MB/s. It is unclear at this point if UHS-III cards will ever hit the market, since it would make more sense to just use the faster SD Express standard. Also, for cards larger than 2TB, the SDUC standard will handle cards up to 128TB. SD Express cards will also be backwards compatible with older bus speeds and be the same size ad SD cards.
Getting back to XQD cards, they are being replaced by CFexpress cards, which are more or less rebranded XQD cards. CFexpress 1.0 cards are what XQD 3.0 cards would have been, as they use PCIe 3.0 instead of PCIe 2.0 like XQD 2.0 cards use, and the PCIe 3.0 bus will allow CFexpress cards to hit a theoretical maximum read speed of 1750 MB/s. CFexpress cards are also backward compatible with select XQD devices that adopt a firmware update to enable CFexpress. B&H currently has CFexpress cards available from SanDisk, ProGrade Digital, Lexar, and Wise Advanced, in capacities ranging from 64GB to 1TB.
Unfortunately, SD Express isn’t available at this time. So, if you want the fastest cards money can buy, you are going to have to stick to UHS-II SD cards, XQD Cards, CFexpress, or CFast 2.0 cards. The choice is up to you.
So, there you have it. No matter what kind of camera you’re shooting with or what your speed needs are, this article is almost certain to have what you’re looking for. With cameras available that can capture rapid-fire shutter bursts, large raw files, and 10-bit internal video, the need for memory cards with fast read and write speeds becomes more necessary every day.
What do you think—are these cards fast enough for you? Feel free to leave your comments below.