No matter what digital camera you shoot with nowadays, you must have some kind of storage where your media is going to be saved to. While some devices like phones and tablets often come with some built-in memory, you will often find yourself looking for ways to expand that storage by using memory cards or other external storage accessories. And if you shoot with a dedicated digital camera, you will find that it does not offer any kind of storage and you will need to buy at least one memory card in order to be able to store captured images. That’s how a quest for selecting the best memory card begins. Choosing memory cards can be a very frustrating experience, since there are so many different types of memory cards with so many different features and price points. In this article, we will explore memory cards in detail and give you everything you need to know about them.
First, we will explore the different types of memory cards available. Then we will go over the different classes of memory cards. After that, we will show you ways how to read and understand information written on memory cards. And lastly, we will give you some of our tips and recommendations for selecting the best memory cards available on the market today.
Memory Card Types / Form Factors
Here is a quick summary of different types of memory cards available on the market today, along with their dimensions and abbreviations:
|#||Memory Card Name||Abbreviation||Dimensions (WxLxH)|
|1 Discontinued / Uncommon|
|1||Secure Digital 1||SD||24.0 x 32.0 x 2.1mm|
|2||Secure Digital High Capacity||SDHC||24.0 x 32.0 x 2.1mm|
|3||Secure Digital Extended Capacity||SDXC||24.0 x 32.0 x 2.1mm|
|4||MicroSD / MicroSDHC / MicroSDXC||MicroSD / MicroSDHC / MicroSDXC||11.0 x 15.0 x 1.0mm|
|5||Memory Stick, Memory Stick PRO 1||MS||50.0 x 21.5 x 2.8mm|
|6||Memory Stick Duo / PRO Duo / PRO-HG Duo||MSD / MSPD / MSPDX||20.0 x 31.0 x 1.6mm|
|7||CompactFlash Type I||CF-I||42.8 x 36.4 x 3.3mm|
|8||CompactFlash Type II 1||CF-II||42.8 x 36.4 x 5.0mm|
|9||CFast||CFast||42.8 x 36.4 x 3.6mm|
|10||XQD||XQD||38.5 x 29.6 x 3.8mm|
|11||CFexpress||CFexpress||38.5 x 29.6 x 3.8mm|
It is important to note that the above table is limited to the most popular memory cards and form factors used on digital cameras and camcorders. Many other memory card types were introduced and then abandoned over the years, but I am not going to go through each one of them. Let’s get started!
Secure Digital (SD)
Secure Digital cards, or shortly “SD cards” were jointly developed by SanDisk, Panasonic and Toshiba and introduced in 1999 for use in portable devices. The three companies later formed the SD Card Association to create, promote and enforce SD card standards across the industry. With a fairly small size of 24.0 (W) x 32.0 (L) x 2.1mm (H), relatively low cost of production and adoption by many manufacturers, SD cards quickly became an industry standard. However, due to file system and other limitations, SD cards could only hold up to 2 GB of data maximum, so new standards had to be developed in order to allow larger capacity memory cards. The nice thing about the SD card specification, is that it allowed the SD Card Association to keep the same physical dimensions and appearance, while being able to create newer generation SD cards with higher capacities and speeds. Today, the original SD cards have been fully discontinued and they have been replaced by the newer-generation SDHC and SDXC cards. Quick Summary: Obsolete format, move on to SDHC or SDXC cards.
Secure Digital High Capacity (SDHC)
With a 2 GB capacity limit, the original SD cards were obviously no longer sufficient, so the SD Card association had to come up with a new specification that allowed larger capacity cards. In January of 2006, a new standard was developed that not only increased card capacity to up to 32 GB in size, but also doubled the performance of the cards, allowing much faster read and write speeds. This standard was named “Secure Digital High Capacity”, indicating the increased capacity of these cards. Unfortunately, older SD card readers in cameras and computers were not compatible with SDHC cards, until their firmware was updated to be able to support the new card standard, whereas SDHC memory card readers were backwards compatible to be able to read both SD and SDHC memory cards. SDHC cards are fairly common to find on the market, although they might soon be phased out by the larger SDXC cards. Quick Summary: You can get older UHS-I and newer UHS-II (more on UHS under Memory Card Speeds) SDHC memory cards, but be warned that SDHC is limited to 32 GB cards only – anything of larger capacity will have to be SDXC.
Secure Digital Extended Capacity (SDXC)
With a maximum capacity of 32 GB (mostly imposed by the limited FAT32 file system) and newer devices pushing a lot more data, especially when capturing high bitrate video, it was time to move up to a new and improved standard and that’s how Secure Digital Extended Capacity (SDXC) was born. Maximum card size was increased to theoretical 2 TB maximum (2048 GB) and the file system was switched to exFAT, developed by Microsoft. The newest SDXC standards are very robust, allowing very fast transfer speeds of up to 312 MB/sec using UHS-II bus. Quick Summary: If you need SD memory card capacities above 32 GB, SDXC is the only way to go. Whether you choose SDHC or SDXC does not matter – the bus speed (UHS-I vs UHS-II) and the rated memory card speeds for both read and write operations are going to be more important.
MicroSD / MicroSDHC / MicroSDXC
MicroSD memory cards were born due to SD cards being too big for mobile phones. Initially developed by SanDisk, MicroSD was later on embraced and standardized by the SD Card Association, which announced the form factor in 2005. The initial MicroSD memory cards were slow and their capacities were limited to 2 GB due to the FAT16 file system, just like SD cards. However, the SD Card Association was quick to release the next generation SDHC cards that lifted those limits. And with the introduction of SDXC that took advantage of the exFAT file system, it became possible to make cards larger than 32 GB in size, with much faster read and write speeds. MicroSD cards quickly gained popularity among portable device manufacturers for their small size – at just 11.0 (W) x 15.0 (L) x 1.0mm (H), these cards are the smallest memory cards available on the market today and they have been embraced by many mobile phone and tablet manufacturers. Quick Summary: MicroSD is a popular format for small portable devices, so if you have a phone or a compact camera that utilizes MicroSD cards, you will need to buy MicroSDHC or MicroSDXC cards.
Memory Stick / Memory Stick PRO
Sony introduced the Memory Stick in 1998 and started using it on Sony cameras, camcorders, PCs and PlayStation Portable devices as a proprietary memory card format. Although these memory cards were initially available in small capacities, a newer revision of the card in the form of Memory Stick PRO was introduced in 2003 that expanded memory capacity even further. With a fairly large footprint of 50.0 (W) x 21.5 (L) x 2.8mm (H) and high pricing, these memory cards could not get enough traction to be able to gain a significant market share when compared to SD cards, so Sony had to come up with ways to decrease the physical size of the cards. Both Memory Stick and Memory Stick PRO cards were therefore short-lived, with Memory Stick Duo form factor taking over. Quick Summary: Both Memory Stick and Memory Stick PRO cards have been obsolete for many years now and you can no longer purchase them from most retailers.
Memory Stick Duo / PRO Duo / PRO-HG Duo
With the introduction of Memory Stick Duo form factor that measured smaller than the original Memory Stick at just 20.0 (W) x 31.0 (L) x 1.6mm (H), Sony thought that it could compete directly with the SD format and capture a larger market share of the memory card market. Unfortunately, due to Sony’s higher pricing strategy, the plan did not work out and Sony lost most of its market share to SD, which later became the most popular memory card format on the market globally. Still, Sony continued to push the Memory Stick to its own products, eventually coming up with faster and higher capacity memory cards like Memory Stick PRO Duo and PRO-HG Duo, which offered much faster transfer rates of up to 60 MB/sec and theoretical capacities up to 2 TB. Today, Sony is the only memory card manufacturer that continues to produce and support these cards. Quick Summary: Sony completely lost the memory card war to SD and all of its Memory Stick products are a thing of the past.
CompactFlash Type I (CF-I)
CompactFlash (CF) was first introduced by SanDisk in 1994 and it quickly gained traction compared to all other formats of its time, because it offered solid performance and it was not as prone to bending or breaking as some other memory card types, thanks to its denser shell construction. As a result, a number of camera manufacturers like Nikon and Canon adopted CF as their standard in high-end cameras, making CF popular among enthusiasts and professionals. CompactFlash Type I (CF-I) memory cards are the most common and have dimensions of 42.8 (W) x 36.4 (L) x 3.3mm (H) – these are the memory cards that were widely adopted by many cameras and portable devices. The biggest issue with CF cards turned out to be their large size and pins, which are prone to bending on memory card readers. Another limitation of CompactFlash is that it utilizes the slow Parallel ATA / IDE bus. Despite the introduction of newer CF-I revisions that allowed these cards to reach up to 167 MB/sec speeds in Ultra DMA Mode 7 (more on CF memory card speeds below), the bus itself imposed the limit on maximum throughput. As a result, new standards had to be developed to move away from CF cards. Quick Summary: Unless you have a camera that still uses CF cards, you should not be looking into them, since they have already been replaced by much faster CFast, XQD and CFexpress memory cards.
CompactFlash Type II (CF-II)
CompactFlash Type II (CF-II) memory cards were developed in order to allow memory cards to be used as “microdrives” (miniature hard disks) or adapters to read other memory cards. Therefore, the only difference between CF-I and CF-II is the physical height. CF-I cards have a height of 3.3mm, whereas CF-II cards are a bit thicker at 5mm. Both use exactly the same type of connection, but since CF-II cards are physically thicker, memory card readers need to be able to accommodate them. Since the idea of microdrives never got real traction and faster flash memory took over due to lower cost, capacity and reliability, most manufacturers including Nikon ended up dropping support for CF-II cards in their cameras. Quick Summary: CF-II cards are not even available to buy, since CF-II format was only developed to be used for microdrives and memory card adapters.
To get away from the slow Parallel ATA / IDE bus, a new CompactFlash memory card variant called “CFast” was invented, which utilizes the much faster Serial ATA bus. The first version of CFast (1.0 / 1.1) allowed to reach up to 300 MB/sec speeds, whereas the newer CFast 2.0 standard released in 2012 took advantage of the Serial ATA 3.0 bus, doubling the throughput potential to up to 600 MB/sec. It is important to point out that although the physical dimensions of CFast cards are very similar to those of CompactFlash cards, they are not backwards compatible due to differences in interfaces. Unfortunately, the mass adoption of CFast was too slow (aside from the Canon 1D X II, the Hasselblad H6D-100C and a handful of video recording cameras, no other products have adopted CFast) and as of 2016, it has already been technically replaced by the newer and much faster CFexpress standard. Again, the bus was the biggest reason why CFast had to go. Quick Summary: CFast is already dead, since it has been replaced by the new CFexpress standard based on the XQD form factor, so do not waste your money by buying these cards.
XQD was a new memory card form factor introduced in 2010 by SanDisk, Sony and Nikon. Since it is based on the fast PCI Express interface, it clearly stood out from all other memory cards developed before, so it was immediately picked up by the CompactFlash Association for development. Essentially, XQD replaces both CompactFlash and CFast as the new form factor. With its 38.5 (W) x 29.8 (L) x 3.8mm (H) dimensions, it is physically smaller than CompactFlash / CFast cards and it has a much superior build than both SD and CF cards, since the cards are denser than SD and they no longer utilize pins on the host that could easily break or bend. Among camera manufacturers Nikon was the first to standardize on XQD cards with its Nikon D4, D4S, D5, D850, D500, Z7 and Z6 cameras using single or dual XQD memory slots. Although the first N-Series XQD cards were limited to 125 MB/sec read and 80 MB/sec write speeds, the last generation G-Series XQD cards have been able to reach much faster 400 MB/sec read and 350 MB/sec write speeds. With the latest XQD version 2.0 standard, the maximum theoretical throughput of XQD cards has been pushed up to 1 GB/sec, although no such cards exist today. Similar to CFast, XQD has also seen a very slow adoption rate. At the moment, there are only three manufacturers that make XQD cards: Sony, Nikon and Delkin. Quick Summary: XQD is fast and capable, but it will eventually be replaced by CFexpress.
In September of 2016, the new CFexpress standard was announced, which is capable of utilizing NVMe storage for low overhead and latency, capable of pushing almost 2 GB/sec. The first iteration of CFexpress uses the XQD form factor, but requires a CFexpress capable reader/writer on the host. Some cameras, such as the Nikon Z6 and Z7 were initially released only with XQD memory card support despite having a CFexpress compatible memory card slot. Nikon planned on releasing a firmware update to bring compatibility to these cameras after CFexpress goes official. Considering the technology present in CFexpress cards, they will likely become the gold standard for most high-end devices in the future. Quick Summary: CFexpress is currently the fastest and the most capable memory card format on the market, and will likely be the default choice for future-generation stills and video cameras.
Memory Card Sizes
Memory cards obviously come in different sizes. While older memory cards were limited to megabytes, newer memory cards are much larger in comparison and can be commonly found in 64 GB and larger sizes. Some of the latest generation memory cards offer 512 GB memory card capacities. Memory card capacity is typically clearly indicated on top of every memory card and you should be able to easily find it. If you are wondering how big of a card you should get, it really depends on a number of factors such as: what you shoot, how much resolution your camera has, whether you shoot RAW or JPEG, what RAW compression option you use when shooting RAW and whether you shoot a lot of continuous action. For example, a 16 GB card might be sufficient for a portrait photographer who shoots selectively with a medium resolution camera, whereas a wildlife photographer who shoots many bursts of images, or a landscape photographer who takes high-resolution panoramic images might find even 64 GB memory cards to be somewhat limiting for their needs.
Memory Card Speeds
Memory cards can also vary greatly in speed, or how fast they can read and write information. Unfortunately, this is where things can get quickly confusing, because speed ratings and how they are marked vary greatly by memory card type. In this section, we will take a look at how memory card speeds are marked on SD, CF and XQD / CFexpress memory cards.
SD Memory Card Speed Classes
The SD Card Association came up with a way to define SD card speed through something called “Speed Class”, which defines minimum sequential writing speed a memory card can provide. In addition to that, there is also bus speed, which is typically defined as something like “UHS”, which shows the theoretical maximum a card can provide over the bus. There are also UHS Speed Class and Video Speed Class specifications, which define minimum sequential write speeds even further. Let’s start by looking into different bus interfaces and their limits. Below is a short table that summarizes different bus interfaces and their potential bus speeds:
|Bus Inteface||Compatible Memory Cards||Maximum Bus Speed|
|High Speed||SD, SDHC, SDXC||25 MB/sec|
|UHS-I||SDHC, SDXC||104 MB/sec|
|UHS-II||SDHC, SDXC||312 MB/sec|
|UHS-III||SDHC, SDXC||624 MB/sec|
As you can see, there is a big difference between High Speed, UHS-I, UHS-II and UHS-III cards in terms of maximum bus speed. While the original cards were pretty much capped at 25 MB/sec, the UHS-I bus interface lifted that to 104 MB/sec and the newer UHS-II bus was able to triple that potential at 312 MB/sec. The newest UHS-III standard is very new, but it enables insane theoretical speeds of up to 624 MB/sec.
It is important to understand that cards with a faster bus speed also require a memory card reader / writer that can support that bus speed. For example, if you purchase a memory card with a UHS-II bus interface, the memory card slot on your camera must also be UHS-II compatible, or you will experience all kinds of performance and reliability issues. The same goes for a memory card reader on your computer – it also must be UHS-II compatible in order to support the higher speeds.
Besides the bus interface, you might also find other speed classes that are marked on SD memory cards. Let’s go over those now:
|Minimum Sequential Write Speed||Speed Class||UHS Speed Class||Video Speed Class|
|2 MB/sec||Class 2 (C2)|
|4 MB/sec||Class 4 (C4)|
|6 MB/sec||Class 6 (C6)||Class 6 (V6)|
|10 MB/sec||Class 10 (C10)||Class 1 (U1)||Class 10 (V10)|
|30 MB/sec||Class 3 (U3)||Class 30 (V30)|
|60 MB/sec||Class 60 (V60)|
|90 MB/sec||Class 90 (V90)|
This all sounds pretty confusing doesn’t it? Well, those are the markings you will commonly find on many SDHC and SDXC memory cards out there. Let’s take a look at a real memory card and see if we can make some sense from all the information provided on it:
- Maximum Read Speed – This is the maximum sequential read speed the memory card is capable of in Mega Bytes per second (MB/sec). Please note that write speeds are rarely ever published on memory cards and you will need to find that information in memory card manual or listed specifications. In this case, the maximum read speed of the SD card is 300 MB/sec.
- Type of SD Memory Card – You should also be able to locate the proprietary SD card logos on memory card labels that indicate whether the card is of SD, SDHC or SDXC type. In this particular case, it is an SDXC memory card.
- UHS Bus Speed – UHS bus speed is also often published directly on memory card labels. If it is a UHS-I card, you will just see roman numeral one (I), whereas if it is a UHS-II card, you will see roman numeral two (II), as in the case of the above card.
- SD Speed Class – This number indicates what SD Speed Class card it is, per table above. As in the above case, all modern SD cards should be rated at 10 minimum, which guarantees minimum sequential write speed of 10 MB/sec.
- UHS Speed Class – Aside from UHS bus speed, you will also typically find a UHS speed class label. In this particular example, I can see that the card is rated at minimum 30 MB/sec write speed, thanks to this U3 label.
- Memory Card Capacity – The capacity of the memory card is typically displayed in large numbers. As can be seen here, this memory card has a total capacity of 128 GB.
Now that you can read SD memory cards, let’s take a look at CompactFlash cards and how you can read them.
CompactFlash Card Speed Classes
Unfortunately, memory card speeds and classes can vary greatly depending on what form factor you are looking at. As explained above, CompactFlash cards use Parallel ATA / IDE bus and therefore their speed ratings are influenced by the maximum potential speed of the Ultra DMA interface, just like with older hard drives. Below is a table that summarizes 7 different Ultra DMA modes with their corresponding maximum transfer rates:
|Ultra DMA Mode||Also Known As||Maximum Transfer Rate|
|Ultra DMA 1||25 MB/sec|
|Ultra DMA 2||Ultra ATA/33||33.3 MB/sec|
|Ultra DMA 3||44.4 MB/sec|
|Ultra DMA 4||Ultra ATA/66||66.7 MB/sec|
|Ultra DMA 5||Ultra ATA/100||100 MB/sec|
|Ultra DMA 6||Ultra ATA/133||133 MB/sec|
|Ultra DMA 7||Ultra ATA/167||167 MB/sec|
CompactFlash cards are technically limited by the fastest Ultra DMA mode 7, so it is impossible to develop faster CompactFlash cards in the future – they will always be limited to a maximum throughput of 167 MB/sec.
Thankfully, reading CompactFlash cards is a bit easier when compared to SD cards:
- Memory Card Capacity – The capacity of the memory card is typically displayed in large numbers. As can be seen here, this memory card has a total capacity of 128 GB.
- Maximum Read Speed – This is the maximum sequential read speed the memory card is capable of in Mega Bytes per second (MB/sec). Please note that write speeds are rarely ever published on memory cards and you will need to find that information in memory card manual or listed specifications. In this case, the maximum read speed of the SD card is 160 MB/sec.
- Minimum Write Speed – This is the minimum sustained write speed the memory card can deliver. As you can see, this particular card is guaranteed to be able to write at least 65 MB/sec.
- Ultra DMA Mode – Most cards will list their Ultra DMA Mode on the cover, which will give you a good indication of its potential. This particular CF card from SanDisk has Ultra DMA 7 mode, which is why it can reach top speeds of 160 MB/sec.
Modern cards are even easier to read in comparison. For example, CFast, XQD and CFexpress cards now fully list both read and write speeds right on memory card labels, so aside from those numbers, memory card capacity and perhaps memory card generation, you no longer have to worry about any other numbers that might need to be decrypted.
Memory Card Brands
As of today, there are many different memory card companies that manufacture memory cards. Some of them truly manufacture memory cards, while others use the same OEM parts and simply slap their own labels on top. Some of the biggest names in the industry are: SanDisk, Sony, Samsung, Transcend, Kingston, PNY Technologies, Toshiba, Verbatim and ADATA. Lexar used to be one of the most popular memory card brands, but its parent company Micron announced that Lexar will no longer be manufacturing memory cards for consumers, so their retail division is now defunct…
When it comes to memory cards, I have always been a strong advocate of going with a brand you can always trust. While Lexar certainly resulted in some headaches for me in the past, particularly with their unreliable SD cards, SanDisk has always been my top preference for memory cards, so it is a brand I can always recommend to our readers. I have also used memory cards from Sony and Samsung, which turned out to be pretty decent for their prices…
If you are looking ahead into the future and wondering which memory card formats are future-proof and will survive, I would argue that there are only three: SD, MicroSD and CFexpress. Everything else in my opinion will eventually phase away – it is just a matter of time!
Memory Card Recommendations
Below are my top choices for memory cards:
- SD Cards: If your camera is limited to UHS-I interface, then go for the SanDisk 64 GB Extreme Pro UHS-I SDXC Memory Card. It is perhaps the best UHS-I memory card available on the market today thanks to its reliability, maximum read speed of 170 MB/sec, write speed of 90 MB/sec and a reasonable price. If your camera supports fast UHS-II memory cards, the big step up is the SanDisk 64 GB Extreme Pro UHS-II SDXC Memory Card, which can read up to 300 MB/sec and write up to 260 MB/sec speeds.
- MicroSD Cards: Once again, depending on whether your device can support UHS-I or UHS-II, you will want different cards. If I were to pick a UHS-I card, it would surely be the SanDisk 64 GB Extreme Plus UHS-I MicroSDXC card. And if I wanted to step up to UHS-II, I would surely go with the SanDisk 64 GB Extreme Pro UHS-II MicroSDXC memory card.
- XQD Cards: There are only a couple of manufacturers that are currently making XQD cards, so there is not much to choose from. I personally use the Sony 64 GB XQD G-Series Card, but Delkin also makes a 64 GB XQD card that is similarly priced. If I wanted something with a larger capacity, I would personally go with the 120 GB version of the Sony card.
I hope you found this article useful. If you have any questions or feedback, please let me know in the comments section below.