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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 for external storage. With consumers demanding higher resolution and less compressed video from cameras, manufacturers have responded by supplying more and more capable memory cards. 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.
When memory cards list their 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 the Nikon D5’s burst mode of 12 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 GH4 records at 100 Mb/s, remember that is only 12.5 MB/s.
Luckily, memory cards have a number of 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.
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 we aren’t there yet. This metric does not affect speed at all; an SDHC card can be just as fast as a SDXC card, and often, they are.
Some SD cards have UHS (Ultra High Speed) Classifications. A UHS (Ultra High Speed) Classification determines the maximum speed at which a memory card can read. This 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.
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 video. 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 whatever its class. Some cards may write a lot faster, especially since the fastest speed class is currently just 30 MB/s, but you can be comfortable knowing that any card with a speed class rating will never write slower than that speed. Also remember there are eight bits in one byte, 30 MB/s is 240 Mb/s. Some popular speed class ratings used on SD cards today are:
The SD Association has also recently introduced a Video Speed Class rating, designed to identify cards capable of 8K, 4K, 3D, and 360° video. This speed class is just another way of verifying the minimum sustained write speeds of cards, but it goes higher than both Standard Class ratings and UHS Speed Class ratings. It is made up of:
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, Class U3 cards. Luckily, we carry a number of UHS-II / U3 cards from a few manufacturers. SanDisk Extreme PRO UHS-II cards are available in 16GB, 32GB, 64GB, and 128GB capacities, and offer read speeds up to 300 MB/s and write speeds up to 260 MB/s, which should satisfy the most bandwidth-hungry cameras. Delkin also offers 32GB, 64GB, 128GB, and 256GB UHS-II cards with a read speed of 285 MB/s and a write speed of 100 MB/s. Lexar’s Professional 1000x UHS-II cards are available in capacities of 16GB, 32GB, 64GB, 128GB, and 256GB, and offer a slightly slower maximum read speed of 150 MB/s and a maximum write speed of 80 MB/s. Lexar also manufactures the Professional 2000x UHS-II series in capacities of 32GB, 64GB, and 128GB that deliver a maximum read speed of 300 MB/s and a maximum write speed of 260 MB/s.
If you do not have a UHS-II-capable camera or computer but still need a fast card, take a look at the SanDisk Extreme Pro UHS-I U3 memory card line, available in 32GB, 64GB, 128GB, and 512GB capacities. These cards offer read speeds up to 95 MB/s and write speeds up to 90 MB/s, very close to the maximum possible speed of UHS-I. Lexar’s Professional UHS-I cards range in capacity from 16GB to 512GB and come as U1 or U3. While all of these Lexar cards offer read speeds up to 95 MB/s, the U1 media offers write speeds up to 10 MB/s, and the U3 cards max out at 45 MB/s.
MicroSD cards are essentially miniaturized SD cards, and share the same UHS and class properties as their full-sized brethren; so just like full size SD cards, the fastest microSD cards are UHS-II, class U3 cards. Currently, Lexar offers its Professional UHS-II 1000x, Class U3 cards in capacities of 32GB, 64GB, and 128GB, while offering read speeds up to 150 MB/s and write speeds up to 45 MB/s. Lexar also offers the same capacities for its Professional 1800x UHS-II lineup, which provides maximum read speeds of 270 MB/s and maximum write speeds of 115 MB/s. SanDisk’s Extreme PRO UHS-II cards come in capacities of 64GB and 128GB, offering read speeds up to 275 MB/s and write speeds up to 100 MB/s.
However, UHS-II microSD cards are new, and the chances are that your microSD-compatible device won’t be 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 UHS-1 U3 rated microSD cards in 32GB and 64GB capacities. These cards offer up to 99 MB/s read speeds and 55 MB/s and 80 MB/s write speeds, respectively. SanDisks’s fastest microSD cards comprise the UHS-I U3-rated Extreme PLUS line, which offer maximum read speeds of 95 MB/s and maximum write speeds of 90 MB/s. They are available in 16GB, 32GB, and 64GB capacities, along with a 128GB card offering read speeds up to 90 MB/s and write speeds up to 60 MB/s. Additional 128GB UHS-I U1-rated microSD memory cards are available from Lexar, Delkin, and PNY. Lexar’s 128GB offering supports read speeds of up to 95 MB/s, along with a minimum write speed of 10 MB/s, the Delkin 128GB microSD card comes with 285 MB/s read speed and a 100 MB/s write speed, and the PNY 128GB microSD card features a maximum read speed of 85 MB/s and a minimum write speed of 10 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 slower than the fastest SD cards, though they are still quite fast. 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 will most likely be a lot closer to the maximum speed; however, since manufacturers don’t share that information, it is difficult to verify.
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.
Because the maximum speed of CompactFlash cards has been capped at 167 MB/s, for a while almost all card manufacturers 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, available in capacities between 16GB and 256GB. Lexar rates these cards as having a 160 MB/s maximum write speed and 155 MB/s maximum read speed, as well as 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 120 MB/s, are a bit slower than the Lexar and SanDisk cards. All of 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.
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 the fastest CF or SD cards available.
Currently, Sony and Lexar are the only XQD memory card manufacturers. Sony’s XQD G Series and Lexar’s 2933x cards are the fastest ones around. Available in capacities of 32GB, 64GB, and 128GB, they are XQD 2.0 compliant and offer read speeds up to 440 MB/s and write speeds up to 400 MB/s. When it comes to speed, these cards give computer SSD drives a run for their memory. If you don’t need your XQD cards to be quite that fast, Sony’s XQD M Series offers the same capacities with read speeds up to 440 MB/s and write speeds up to 150 MB/s, while Lexar also offers 1400x media, with read speeds up to 210 MB/s and write speeds up to 185 MB/s.
Despite the fact that 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 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 isn’t really an issue.
Although this is not related to speed, please be aware of CFast Type 1 vs. CFast Type II. This is not to be confused with CFast 1.0, which operates at SATA I (1.5 Gb/s) speeds and CFast 2.0, which operates at SATA III (6 Gb/s) speeds. CFast Type I and Type II refer to the thickness of the physical card media, with Type II cards being slightly thicker (5mm) than Type I (3.3mm). Thus, a CFast Type II card cannot be used in a device that only supports CFast Type I, but Type I cards can be used with Type II devices.
Currently, SanDisk, Delkin Devices, Transcend, and Hoodman offer CFast 2.0 cards, while Lexar makes 3500x and 3600x versions. These cards are available in capacities ranging from 64GB to 256GB and all features 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 510-540 MB/s and write speeds ranging from 370-455 MB/s.
So, if its performance you need, you have to pick sides—CFast 2.0, XQD, or UHS-II. It’s all up to you—well really, it’s up to device manufacturers, but at least now you know how to find the fastest cards available. Questions? Use the Comments section, below.