It’s safe to say that in today’s predominantly digital world, memory cards have overtaken film as the primary recording media for consumer and professional photo and video use. Just as analog cameras were designed to work with a specific film format, such as 35mm or 120 roll film, or large-format sheet film, digital cameras are likewise built to work with one or two specific memory card formats. However, once you’ve established which memory card format is compatible with your camera, such as CompactFlash (CF), Secure Digital (SD), XQD, or CFast, how does one go about choosing from the available models that each card format offers?
While the purpose of this article is to discuss suitable memory cards for photo and video use, there are a few technical details that need to be cleared up first. First, there is a difference between bits and bytes. 8 bits equals 1 byte, and consequently, 8 megabits, or 8 Mb equals 1 megabyte, or 1MB. This is an important detail to realize, because people will often see that their camera records video at 100 megabits per second (Mb/s) and think “Oh, I need a card that records at 100 megabytes per second (MB/s)” when 100 Mb/s converts to 12.5 MB/s.
Second, it’s important to be familiar with read speeds versus write speeds. Manufacturers don’t always advertise their write speeds, so unless a card’s write speed is explicitly stated, any speed written on the front of a card, such as a CF or SD card, is the maximum achievable read speed, but not the sustained read speed. Much in the way a CPU has a base clock speed and an over-clocked speed, sustained and maximum read and write speeds function in a similar fashion. While a memory card may be able to achieve a read speed of 160 MB/s, or a write speed of 90 MB/s, it will rarely be able to sustain those speeds for long periods of time. This is not to say that sustained read/write speeds can’t reach high values. They can, but they won’t be able to sustain their maximum advertised speeds consistently.
Along the lines of speed ratings, it’s also important to be able to convert card speeds with an “x,” such as 1066x, into MB/s. This is accomplished by multiplying 1066 by 150 and then dividing by 1,000. Thus, a card with a speed rating of 1066x has a maximum read speed of 160 MB/s.
When working with SD cards, it’s not uncommon to see things such as the number 4, 6, or 10 enclosed within the letter C, or perhaps a roman numeral I or II, and even a 1 or 3 within the letter U. A 4, 6, or 10 refers to the “Class” of a card, or its minimum-rated sustained write speed. A Class 10 card is rated to never write slower than 10 MB/s, and the number 1 or 3 within the letter U refers to the U1 or U3 speed class rating. U1 is identical to Class 10 and means that a card is certified to write at a minimum of 10 MB/s, while U3 cards have been certified to never write slower than 30 MB/s, with the difference being that “U” cards are designed for SD cards that employ the UHS-I or UHS-II bus.
It’s also important to note that not all U3 cards have the same minimum write speed. A card could be rated U3 and write at 60 MB/s. Along these lines, the SD Association created the Video Speed Class rating, designed to identify cards capable of 8K, 4K, 3D, HFR, HDR, 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 V6 (6 MB/s), V10 (10 MB/s), V30 (30 MB/s), V60 (60 MB/s), and V90 (90 MB/s).
All in all, what does this discussion about card speeds mean? Essentially, if your card is rated to handle faster bitrates, it will be able to record more advanced types of media. Uncompressed, 14-bit raw files from the Nikon D850 can reach around 92MB, while the D5 delivers raw files around 45MB, and you’d better believe that the upcoming Sony Alpha a7R IV is going to produce some raw files of gargantuan volume. The D5 is also able to shoot with a burst mode of 12 frames per second, and while DSLR cameras have an internal buffer to store photos as they’re being taken, the buffer can only hold so much. If a memory card has a faster write speed, a camera’s buffer will be cleared more quickly, allowing new photos to be taken. The same stands true for video—cards with faster write speeds will be able to record video that requires higher bitrates, such as 3D and 4K.
Stepping back briefly to burst speeds versus sustained speeds, burst speeds are more important for photography, while sustained speeds are more important for video. The D5’s buffer can hold up to 20 seconds’ worth of raw files at 12 fps, for a maximum of 240 photos. In this case, a card’s burst speed, which cannot be sustained for long periods, would be beneficial in quickly clearing out the camera’s buffer over a short period. However, video cameras cannot have the card’s speed drop below the video codec’s bitrate, otherwise there will be dropped frames—hence, the reason video relies on sustained write speeds.
Moving on to cards that are suitable for actual use, the first are CompactFlash (CF) cards. Available in capacities up to 512GB, CF cards are interesting because while they are still widely used in DSLRs, they are based on the now defunct PATA standard. The current CF standard, UDMA 7, allows for read speeds of up to 167 MB/s, which is fast enough for most photo and video uses. SanDisk offers its Extreme Pro, and Extreme series, while Lexar offers a 1066x version. Also notable is Delkin Devices’ 256GB Cinema Memory Card, as well as its Select and Prime series. To browse B&H’s full lineup of CompactFlash cards, click here.
Much more common than CF cards are Secure Digital (SD) cards. Able to support capacities up to 2TB, although the largest cards on the market are 1TB, non-UHS SD media read speeds max out at 25 MB/s, while UHS-I cards max out at 104 MB/s and UHS-II cards max out at 312 MB/s. UHS-II media has a second row of pins, allowing it to achieve this extra speed, but if your device does not have this second row of pins, the card will default to UHS-I speeds. The same standards hold true for microSD cards. SanDisk offers its Extreme PRO UHS-II cards in both SD and microSD formats. Sony makes solid UHS-II SD cards with the SF-G and SF-M series, plus a good selection of UHS-I SD and microSD media, and Lexar makes 633x and 667x UHS-I cards.
If you’re interested in SD cards that have been labeled with the Video Speed Class rating, SanDisk makes V30-rated Extreme PRO and Extreme UHS-I SD media, plus Extreme, Extreme PLUS, and High Endurance UHS-I microSD media. Delkin Devices produces the Advantage SD lineup, and Kingston lets users choose between Canvas Go! and Canvas React SD media. If minimum write speeds of 30 MB/s aren’t sufficient for your needs, consider V60 UHS-II SD media. Lexar makes 1000x, 1667x, and 2000x cards, and there are additional offerings from Sony, ProGrade Digital and Angelbird. For those working with cameras and codecs that have intensive bandwidth requirements, Sony, ProGrade Digital, Angelbird, and Delkin Devices deliver with V90 SDXC UHS-II media.
Are you concerned that microSD cards aren’t receiving any of the Video Speed Class love? Well, don’t be, since Delkin Devices has this handled. Its Select and Advantage cards are UHS-I and V30 rated, Prime media receives a boost to UHS-II and V60, and the Power series is rated UHS-II and V90.
While less common and only supported in a handful of devices, such as the Nikon D5, D850, D500, and Sony FS7, XQD cards are the official replacement for CF cards, although these two formats are not interchangeable. XQD cards are based on the PCIe standard (with an 8 Gb/s bus speed), feature read speeds up to 440 MB/s, write speeds up to 400 MB/s, and are currently available in sizes up to 240GB. Sony produces G Series XQD media and Delkin Devices makes Premium XQD cards.
CFast cards are based on the SATA standard most commonly found on computer drives, though CFast card slots are used in cameras such as the Canon EOS-1D X Mark II, Blackmagic Design URSA Mini Pro 4.6K, URSA Mini Pro 4.6K G2, and URSA Mini 4K. CFast 1.0 uses the SATA I (1.5 Gb/s) standard, while CFast 2.0 uses the SATA III (6 Gb/s) standard. This isn’t to be confused with CFast Type I and Type-II, which refers to the thickness of the physical media, with Type II cards being slightly thicker (5mm) than Type I (3.3mm). While Type II cards cannot be used in Type I slots, Type I cards can be used in Type II slots. CFast cards are currently available in capacities up to 512GB and feature read speeds up to 560 MB/s and write speeds up to 495 MB/s. They are manufactured by SanDisk, Delkin, Transcend, ProGrade Digital, and Hoodman, while Lexar makes a 3500x version.
Moving further up, SxS cards are a flash memory standard designed to interface with ExpressCard slots usually found in laptops. SxS cards use a PCIe interface and are the standard storage medium for Sony’s XDCAM EX line of professional video cameras. SxS PRO+ cards, which are offered in the E Series, are designed for 4K video, offer read speeds of up to 437.5 MB/s and write speeds of up to 350 MB/s. When used in 4K workflows, the write speed drops to 162.5 MB/s. SxS cards are used in Sony’s CineAlta cameras and SxS PRO+ feature improved read and write durability.
For those shooting with Sony’s F65, don’t forget about the SRMemory Card platform. Available in capacities up to 1TB and with read/write speeds up to 687.5 MB/s via its PCIe bus, these cards are able to handle demanding 3D, HFR, and 4K media from the F65’s 20.4-megapixel CMOS sensor.
So, what kind of card will you need? That’s dependent on which camera you have and what you intend to use it for. But if it’s performance you’re after, fear not, because this article provides many worthy options. What are your thoughts? Please share them in the Comments section, below.