Memory cards are changing to meet the increasing need for data transfer speed and storage capacity.

The third decade of the 21st century has seen the rise of a new type of imaging professional, known as a ‘content creator’, who produces digital ‘content’ in the form of images, video, animation, audio, printed materials and graphic design that can be published through digital channels. These channels include cinema, online (blogs, vlogs, podcasts, social media, email), radio, TV, exhibitions, events and even at times, printed media. The trick to success involves creating compelling work that goes ‘viral’ by being widely shared.

Image and video recording plays a huge role in creating compelling content and equipment manufacturers have directed their efforts towards creating recording devices that can deliver high quality with high speeds and maximum versatility. This is essential since users are often required to produce content that can be ‘re-purposed’ for widely different media – from widescreen cinema to vlogs that will be viewed on a smartphone.

Recording equipment and data storage play an important role in every content creator’s success. They can drive market developments and determine the capabilities of the cameras we buy and use.

An increasing number of professional and enthusiast-level cameras are being used for both image and video recording, often at professional levels, where high-speed, high-capacity memory cards are essential. (Source: Sony.)

The need for speed

Driven by increasing demands for rich video content, the latest mirrorless cameras are pushing the boundaries of both stills and video capture. Although the ability to record 4K video is virtually universal in cameras and smartphones, only the top models in most manufacturers’ range have been designed for professional use.

The latest cameras sport higher bitrates, more efficient compression, and a range of picture profiles similar to professional video cameras. They also include professional display tools such as focus peaking, zebras, waveform monitoring, and time-coding to enable recorded footage to be integrated with footage captured on professional equipment.

The main issue that has to be addressed is how to handle the huge amounts of image and (to a much lesser degree) audio data that constitutes a video recording. Frame rates of 60 fps (for NTSC systems) and 50 fps (for PAL) are normally required for professional work, which translates to a data throughput of approximately half a gigabyte of data every second.

The fastest, readily-available SD cards have speeds of 300 MB/s, although new UHS-III cards (which are not yet readily available) can double that. Hence the need for faster, higher-capacity cards.

Secure Digital (SD) cards have served us well for more than 20 years, but even the fastest of the readily-available cards – shown on the right in this illustration – are limited to 300 MB/second, which is too slow for the latest cameras. Note the V90 rating on the fastest card denoting its suitability for video recording, although this rating simply indicates a minimum recording speed of 90MB/second. 

New card formats

Until recently, existing Compact Flash (CF) cards have been able to handle the speed and storage capacities of professional DSLR cameras, while Secure Digital (SD) cards have been adequate in most other devices used for recording both stills images and video clips. But times are changing. Neither can meet the transfer speeds and storage capacities required by the current crop of 4K-capable interchangeable-lens cameras – especially those pitched at professional users.

While a few recent cameras have been launched with single media slots, it’s become increasingly common for high-end cameras to have dual slots with one slot each for the new, faster cards. The first to appear was CFast, which was launched in 2009 and has the same physical body as CompactFlash. It was followed by the Sony-developed XQD cards, which have a different form factor from any previous media, which meant cameras required redesigned card slots.

Measuring 38.5 x 29.8 x 3.8 mm, XQD cards initially offered read and write speeds up to 400 MB/s (megabytes per second) read and 350 MB/s write plus storage capacities over 2TB. But, although still available, XQD cards have been supplanted by CFexpress cards.

CFexpress cards

In September 2016, the CompactFlash Association announced CFexpress, the next-generation media standard, which used the same 38.5 x 29.8 x 3.8 mm form factor as XQD cards and had the same contact pins but were much faster. Current CFexpress cards come in three types, two of which are used in consumer photographic and video equipment. Type A cards measure 20 x 28 x 2.8 mm which is similar in size to an SD card, but being thicker are not compatible with standard SD card slots. Manufactured by Sony and used in Sony cameras, they have a theoretical upper speed limit of 1GB/s but are currently only available in two capacities: 80GB and 160GB.


This illustration shows the relative sizes of CFexpress Type A and Type B cards. (Source: Sony.)

CFexpress Type B cards measure 38.5 x 29.8 x 3.8 mm (the same as XQD cards) although they aren’t necessarily compatible with XQD card slots and readers. They are produced by SanDisk, Lexar, ProGrade Digital and Delkin Devices as well as Sony and come in capacities from 64GB to 2TB. Speeds range from 450 MB/s write and 1450 MB/s read to 1430 MB/s write and 1730 MB/s read, with higher speeds usually requiring greater storage capacities. The third type is Type C, which at 54 x 74 x 4.8 mm is close in size to CompactFlash cards but is only used in professional cinema cameras.

Readers should note that while CFexpress Type B and XQD cards share many features, CFExpress uses two PCI lanes of PCI Express bus and doubles XQD’s throughput. In theory, any device with an XQD slot should be able to use CFexpress cards, although it may require a firmware update and it probably won’t support the maximum data transfer speed of the equivalent CFexpress card.
Keep an eye out for the up-coming SD Express cards, which have been touted by the SD Association. Based upon the SD Express 8.0 specification, they are expected to support data transfer speeds of up to 4 gigabytes per second. Lexar looks like being the first company to release the new cards, having announced plans to introduce them in 2022.

How are you affected?

If you buy a new camera with a full frame sensor – especially a high-end model – you’re likely to find it supports one of the new card types. In professional cameras, both card slots will probably support the faster media, while enthusiast-level cameras are likely to have one slot for, say, CFexpress with the other for SD (often UHS 3 or U3 speed class).


Nikon’s flagship mirrorless camera, the Z9 devotes both of its card slots to the new media, with both slots being able to accept CFexpress (Type B) or XQD memory cards.

Enthusiast-level cameras like the Canon EOS R5 have two card slots, one accepting Type B CFexpress cards and the other SD cards.(Source: Canon.)

In a way, this ‘forces’ the transition to the new cards whether the buyer wants it or not. While that may not suit some photographers because, regardless of format, the new cards are much more expensive than existing SD or older CF cards, it does make the latest cameras capable of supporting professional-level video recording and fast, high-capacity burst shooting. Both are necessary for professional sports and journalistic photographers.

Currently the lowest capacity for CFexpress cards is 64GB and it’s likely this will remain as the baseline. Most 64GB cards are priced at around $300. The highest capacity is 2TB, which may be difficult to find and will probably cost more than $1500.

Those who don’t want or need the advantages the new cards provide can choose a camera with one or more SD slots – which may mean opting for an older model. You’ll save money with that approach but your shooting options will be limited – especially for video recording.

If you decide to invest in a new card, in most cases you’ll be buying CFexpress – and you’ll need to know which type (A or B) your camera uses. Sony cameras tend to use type A cards while Canon and Nikon use type B. (Leica and Panasonic are sticking with SD cards for the time being, as is Fujifilm for its medium format GFX cameras.)

So what are the advantages of using the newer, faster cards?

First and foremost is speed. Camera responsiveness and data transfer speeds are usually dictated by the speed of the card in the card slot. Where dual slots are in use, the slowest card determines both recording and review performance – even if you write to only one card or set the camera to sequential recording.

SD cards are not fast enough to support RAW video recording or 4K recordings at high frame rates (100 fps) when using All-Intra compression. For regular 4K/25p video and Full HD at 50 fps using All-Intra compression, UHS speed class 3 or video class V60 cards are minimum requirements.

It’s worth noting that read/write speeds are often slower with higher capacities for a specified card type, due to the additional processing needed to manage the additional chips in the high capacity cards. The difference is usually small but it can affect buffer capacities and video recording performance.

Best card practices

  1. Always format the card in the camera before use and whenever you insert a new card to erase residual data. Never format a card with your computer.
  2. Don’t delete images in the camera, particularly when the card is close to being full. Deleting individual files tells the system which sectors are free to write to, which may require complex assessments. A bad file deletion may cost you more than the file you deleted.
  3. Card failures can happen. If all your cards produce the same problem, suspect the camera, which may have a card write mechanism failure. If only one card fails – especially if you use it in several cameras – the card is likely to be faulty. Carry out a low-level format and try again. If the problem persists, retire the card.
  4. Understand the folder structure and how your computer/software sees it. For still images, there will be a DCIM folder (Digital Camera IMages). Video images may be stored in the DCIM folder but cameras that use the AVCHD standard store movie files in a complex folder structure: PRIVATE/AVCHD/BDMV/STREAM.

Do you need a card reader?

A memory card reader will make it easy for you to connect your camera’s memory card to your computer for downloading files and provide faster file transfers. A reader will also provide more secure and reliable transfers. While it may be as easy to connect your camera to your computer via a USB cable – and the latest USB-2 cables support fast transfers – if the camera’s battery fails while files are being moved across, the transfer will be lost and the memory card may become corrupted.

SD card readers are affordably-priced and simple to use with both laptops and desktop computers. Dual readers like the one shown will also accept the microSD  cards from your phone.

These days it’s more of a ‘nice to have’ device than an absolute necessity, although it’s certainly useful to have readers for the new CFexpress and XQD cards. If you can afford the relatively modest price, an SD reader can be had for less than $50, making it a worthwhile investment. Multi-card readers that have slots for SD, CF and Memory Stick cards are only a little more.

This illustration shows a typical reader for CFexpress Type B cards. It can’t be used for Type A cards.

Prices are considerably higher for the newer CFexpress and XQD card readers (usually $100 to $250) and these readers are specific to one card format. You can’t put CFexpress Type A in a CFexpress Type B reader, and vice versa. However, some CFexpress Type A readers can also ‘read’ SD cards and most CFexpress Type B readers will ‘read’ XQD cards.

Excerpt from Photo Review Issue 91

Subscribe to Photo Review magazine, which gives you bonus access to the current PDF edition.