Flashback: The rise (and fall?) of the microSD card

The recent shopping frenzy has us on the hunt for cheap microSD cards, and sadly, many of us no longer own a phone with a memory expansion slot. It took us back down memory lane and revisited the history of the microSD.

A few years ago we did a memory card review covering MMC, SD, Memory Stick and more. Today we want to focus on the microSD because – for better or for worse – it is the card that wins the format wars.

It’s ancient history by now, and we had an article from over a decade ago documenting the growing popularity of microSDs. With very few exceptions, it is the memory card format of choice for most manufacturers. Come to think of it, this was an easy win: MMC and SD (even the short-lived miniSD) were too big, and only Sony was really pushing the Memory Stick.


Percentage of smartphone manufacturers adopting microSD by 2010

microSD, sometimes called “TransFlash”, was introduced in 2004. The first phone to use the new card format was definitely Motorola – there were a few models in 2004, but evidence suggests the Motorola E398 was the first.

The E396 is capable of playing MP3s and comes with a 64MB card in the box. You won’t be able to fit many songs on it even with heavy compression, but you can always pop it out and get a new card.

Flashback: The rise (and fall?) of the microSD card

The phone holds an important place in history as it was the basis of Motorola’s ROKR E1, the first phone to support iTunes. Apple controlled 75% of digital music sales in 2005, largely due to the success of the iPod. However, Steve Jobs saw the danger that cell phones posed to his pocket music players and wanted to enter that market as well. ROKR was a flop, but probably the next call was a resounding success.

Flashback: The rise (and fall?) of the microSD card

microSD is a smaller version of an SD card. There are some minor differences (aside from what we call size), but they’re so small that a passive adapter can convert from microSD to full-size SD. This is great for inserting the card into your computer to load songs onto it, or to download photos and videos you’ve taken to your phone.

This relationship means that improvements in microSD have gone hand in hand with SD cards. The first major change occurred in 2006 with the introduction of the SDHC – HC “High Capacity” standard.

Previously card capacity was limited to 2GB, SDHC expanded it to 32GB and made support of FAT32 mandatory. This file system allows not only large maps, but also large files (up to 4GB).

Flashback: The rise (and fall?) of the microSD card

The next big leap came in 2009 with the SDXC, or “extended capacity” format. These pushed the limit to 2TB and switched to exFAT, an evolution of the FAT32 file system that allowed for files larger than 4GB.

A few years ago, the SD specification was updated to SDUC, or “Ultra Capacity,” which supports cards up to 128TB, but it’s still a long time before that limit is hit. In fact, even the 10+ year old SDXC format still hasn’t been a limiting factor, as the largest microSD card on the market today has a capacity of 1TB.



The world’s first 1TB microSD card arrives in 2019 and costs $450

Capacity is the most important metric for a microSD card, but there are a few others you should be aware of. “Speed ​​Class” is important for some applications because it guarantees a minimum sequential write speed. The speed rating is usually displayed on the card itself if you know how to read the icon.

The simplest rating is a “Class 2”, marked as a 2 in a C on the card. This means guaranteed cards will never drop below 2MB/s. There are C2, C4, C6 and C10 classes. The faster the card, the faster you can copy files.

Flashback: The rise (and fall?) of the microSD card

Some real-time applications, such as video recording, are so dependent on sustained write speeds that there is a dedicated class for them. They range from V6 to V90, which means 6MB/s (enough for standard definition video) up to 90MB/s (needed for 8K footage).

Here’s a handy chart from the SD Association showing the relationship between sequential write speed and video resolution. Note that this is only an indication, as different cameras use different codecs at different bandwidths.



SD Speed ​​Class required for a given video resolution (and frame rate)

The original SD format required transfer speeds of up to 12.5MB/s, later increased to 25MB/s. The data bus was later upgraded to UHS-I (“Ultra High Speed”), increasing the speed limit to 104 megabytes/second.



A comprehensive overview of SD speed classes

UHS-II is very different from the original format because it adds an extra row of pins. This further increases the transfer rate to 156MB/s in full-duplex mode and 312MB/s in half-duplex mode (ie the data flow is directional or unidirectional respectively). It’s easy to fit an extra row of pins on a large SD card, however, microSD’s size presents challenges.

There are UHS-II microSD cards, but they are rare and expensive. What seems even rarer are devices that support UHS-II microSD cards. Even without UHS-II, these cards are good enough to capture high-resolution video, but the rise of smartphones has brought new challenges.


Higher speeds require more pins – enter UHS-II and SD Express

So far we have discussed memory cards as media storage: MP3 and video. These are still its most popular uses. A more interactive use is to store apps and games, which grow in size and complexity over time.

However, they’re not great map apps because they’re slow otherwise. Videos are recorded sequentially, so only the speed of the sequential counts. Applications and games require fast random access, and most tabs aren’t designed for that.

While some are better than others, the SD Association has introduced application performance ratings. Both describe speed in terms of IOPS (random input/output operations per second). The first class, called A1, guarantees 1500 read IOPS and 500 write IOPS. A few years later came the A2, which raised the read target to 4,000 IOPS and the write target to 2,000 IOPS.

Flashback: The rise (and fall?) of the microSD card

The latest development is SD Express, which simply follows the example of NVMe SSD, using the PCIe data bus. The original specs allowed for a single PCIe 3.0 lane and transfer speeds of up to 985MB/s. So a single PCIe 4.0 lane (or two PCIe 3.0 lanes) is supported up to 1,970MB/s. The maximum speed possible today is achieved via two PCIe 4.0 lanes – up to 3,940 MB/s.

SD Express requires additional pins similar to UHS, which hinders the adoption of tiny microSD cards. As we said, devices that support additional pins are rare.

The Steam Deck can run games from a microSD card, but Valve has only equipped it with a UHS-I slot. This means that transfer speeds aren’t much faster than spinning HDDs (seek times are better, but nowhere near SSDs). The Nintendo Switch also only has one UHS-I slot.



The rise of SD and microSD cards

MicroSD cards are still popular, and their small form factor has earned them a place in action cameras, drones, and more. They find use in portable consoles, although a larger SD card (particularly the SD Express type) would be a better choice.

However, their popularity on smartphones is declining. how did it get here? We’d like to blame streaming services in part: how many MP3 files and videos do you have on your phone? And your friends? With fast 4G and now even faster 5G and falling mobile data costs, streaming has gone from feasible to preferred. Spotify, Netflix, YouTube and more mean you don’t need all the storage space on your phone.

Mobile gaming is now bigger than PC and console gaming combined, but for the above reasons, that won’t drive microSD adoption. A game that is too large to fit in internal memory is too demanding to run on the card.

Another culprit is the increase in built-in storage capacity. 128GB seems to be the average these days, with most people saying they need 128-256GB. With this, there’s not much need for expandable storage.

Flashback: The rise (and fall?) of the microSD card

We know that some of you are absolutely disgusted that most manufacturers have stopped including microSD slots in their phones, especially in high-end phones. Unfortunately, the average consumer seems to care about card slots as much as they do about compact phones. The same goes for regular smartphone manufacturers.

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