Some cameras today are using memory cards that did not exist ten years ago. It is time to again survey the state of memory cards. The last time I wrote about memory cards was 2014.
While many online comments assume Compact Flash (CF) memory cards are antiquated simply because they are larger than SD cards, that’s not true. CF might be considered as antiquated because of limited speed of data transfer – how fast can data be written to the card. CF cards, like older SD cards (UHS-I), may be “slow” when compared to some other card technologies.
For the past ten years, SD (secure digital) cards have dominated the market for cameras and other electronics. Unfortunately, labelling on SD cards can be quite cryptic. A single card may state: 250MB/s, UHS-II, U3, Class 10, V60.
- “C” is original speed class C2 (2 MB/sec), C4 (4 MB/sec), C6 (6 MB/sec), and C10 (10 MB/sec).
- “V” is video speed class V6, V10, V30, V60 and V90.
Memory cards are a form of NVRAM (Non-Volatile Random Access Memory). That implies two things. When the card is removed from electrical power, the data stored on a memory card does not disappear. That data can be accessed randomly; reading and writing is Not limited to serial or linear order.
Faster is better … maybe
There are two reasons but possibly neither reason is important to you.
Capturing video
When capturing video, the data rate out to your memory card will vary depending upon which codec and configurable parameters available with that particular codec. Let’s vaguely consider two examples, assuming the picture resolution is Ultra-High Definition video (a.k.a. UHD or 4K) and 30 frames per second:
- H.264 is maybe 4 MB/sec (32 Mb/s) write to your memory card
- Apple Pro Res 422 can be more than 60 MB/sec (480 Mb/sec) write to your memory card
Capturing bursts of high-resolution photos.
If a camera is going to produce RAW images of file size 30 MB each and you hold down the shutter release, capturing ten frames per second, that’s 300 MB/sec. The camera buffers the images internally until they can be saved to the card. The question is then: how much time before that writing is complete and you can press the shutter release again?
Under the hood
The most important difference between memory card technologies is what you can’t see.
The foundation of SDXC is UHS bus
The foundation of CF is Parallel ATA (PATA) bus interface.
The foundation of CFast is SATA III bus interface.
The foundation of XQD is PCIe.
The foundation of CFexpress is PCIe.
Next Generation is here
CFast is quickly fading away in our rear-view mirror. Some contemporary cameras do still employ these cards, including Blackmagic URSA and the Canon EOS C700.
Second generation XQD 2.0 debuted in 2012. Jointly developed by SanDisk, Sony and Nikon, XQD apparently defeated CFast but has not gained wide adoption. While XQD has been employed in a handful of Nikon cameras, it surprisingly has not appeared in Sony cameras. Perhaps the only non-Nikon camera to use XQD was the XF IQ4 by Phase One.
CFexpress was developed by a broad consortium of companies and, unlike XQD, does not incur licensing fees paid to Sony. Second generation CFexpress type B has the same physical size as XQD but can transfer data faster. Cameras currently supporting CFexpress cards include Canon EOS R5, Nikon D6, Nikon Z9 and Sony α7S III.
XQD and CFexpress can support 6K video and 8K video recording. CFexpress and XQD share the same physical size and durable packaging. Some Nikon Z-series cameras support either in the same card slot.
Consumer cameras will likely continue to use SDHC/SDXC/SDUC cards for several reasons.
- Average consumers do not require durability/ruggedness of XQD and CFexpress.
- Average consumers are not shooting 6K or 8K video
- SD UHS-II cards are far less expensive than XQD and CFexpress cards
The very brief list
SDHC (SD High Capacity): between 4 and 32 GB;
SDXC (SD Xtreme Capacity): up to 2 TB;
SDUC (SD Ultra Capacity): up to 128 TB.
Data Speed
SDHC/SDXC/SDUC UHS-I: 104 MB/sec
SDHC/SDXC/SDUC UHS-II: 312 MB/sec
SDHC/SDXC/SDUC UHS-III: 624 MB/sec
(The only product I can find is Sony SF-G Series Tough SDXC, $188)
CF (Compact Flash): up to 155MB/sec
CFast: up to 600Mb/sec
XQD: up to 1000MB/sec
CFexpress type A : up to 1000MB/sec
CFexpress type B : up to 2000MB/sec
(To date, the fastest card has max write 1600MB/sec and max read 1700 MB/sec)
CFexpress type C : up to 4000MB/sec
Physical size
SD card is 32.0 × 24.0 × 2.1 mm
XQD is 38.5 x 29.8 x 3.8 mm
CFexpress Type A is 20 x 28 x 2.8 mm
CFexpress Type B is same as XQD
CFexpress Type C is 54 x 74 x 4.8 mm
Card Readers
Card readers that support both XQD and CFexpress are very rare. I found one that cost $150.
CFexpress type-A and CFexpress type-B are physically different. Card readers likely support one of these, not both.
Some card readers have multiple slots to accept different card formats. Such readers may only recognize one card at a time; if you insert two cards at the same time, it may only recognize the first card inserted.
To mention a few
The top two brands I have trusted are Lexar and SanDisk. Second tier Transcend. Third tier Kensington. While PNY probably deserves a spot in the top five, I’ve never actually owned a PNY card.
In 2017, Micron sold the Lexar brand. And, according to multiple reports online, a new brand, ProGrade Digital, was founded by some of the old Lexar leadership team.