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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. Smartphones, tablets, and even laptops often rely on memory cards for external storage these days. With consumers demanding both 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, but don’t actually 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. Oftentimes, 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 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, 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 oftentimes are.
SD memory card capacity
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.
UHS classification and max burst speed in MB/s
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:
Speed class ratings: minimum read speeds in MB/s
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 UHS-II U3 cards from a few manufacturers. SanDisk Extreme PRO UHS-II cards are available in 64GB, 32GB, and 16GB capacities, and offer read speeds up to 280 MB/s and write speeds up to 250 MB/s, which should satisfy the most bandwidth-hungry cameras. Delkin also offers a 32GB card with the same 280 MB/s maximum read and 250 MB/s maximum write speeds. For those willing to trade a little speed for more capacity, Lexar’s Professional UHS-II cards are available in 256GB and 128GB capacities and offer a slightly slower maximum read speed of 150 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 128GB, 256GB, 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.
MicroSD cards are essentially miniaturized SD cards, and share the same UHS and class properties as their full-size brethren; so just like full size SD cards, the fastest microSD cards are UHS-II, class U3 cards. Currently Lexar offers UHS-II, class U3 cards in capacities up to 128GB. These cards offer read speeds up to 150 MB/s.
However, UHS-II microSD cards are very new, and the chances are that whatever device you are using that takes microSD cards, it 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 50 MB/s write speeds. SanDisks’s fastest microSD cards are the UHS-I U3-rated Extreme PRO line, which offer maximum read speeds of 95 MB/s and maximum write speeds of 90 MB/s. They are available in 32GB and 64GB capacities. If you need more than 64GB of space along with high speeds Lexar, Delkin and PNY offer 128GB UHS-I U1-rated cards with maximum read speeds of at least 50 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 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 800x, 1066x, 400x, 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, though their write speeds 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 XQD Cards are the reason CompactFlash cards aren’t getting a speed update, as they are the CompactFlash Association’s official replacement for CompactFlash cards. XQD cards 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.
The Fastest XQD Cards Currently, Sony and Lexar are the only XQD memory card manufacturers. The Sony XQD Version 2.0 cards in 32GB, 64GB, and 128GB capacities are the fastest ones around. All three cards offer extremely fast read speeds of up to 400 MB/s and write speeds of up to 350 MB/s. When it comes to speed, these cards give computer SSD drives a run for their money. If you don’t need your XQD cards to be quite that fast, Lexar also offers XQD Cards in 64GB and 32GB capacities with read speeds up to 200 MB/s.
CFast 2.0 Cards 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.
The Fastest CFast 2.0 Cards Currently, Lexar, SanDisk, and Transcend offer CFast 2.0 cards. The Lexar Professional CFast2.0 cards are advertised as having up to 510 MB/s read speeds and come in 256GB, 128GB, 64GB, and 32GB capacities. Transcend also offers 256GB and 128GB CFast 2.0 cards with 510 MB/s read speeds. For even more speed check, out the SanDisk Extreme PRO CFast 2.0 cards that can reach read speeds up to 515 MB/s, which would makes them the top contender for the fastest memory card mentioned in this article.
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.