The recent shopping spree had us looking for bargains for microSD cards and with that came the sad realization that many of us no longer have phones with a memory expansion slot. It sent us on a walk down memory lane to revisit the history of microSD.
A few years ago, we did a memory card retrospective, covering MMC, SD, Memory Stick and others. Today we want to focus exclusively on microSD because – for better or worse – it was the card that won the format war.
That’s ancient history now, we have an article from over a decade ago that chronicled the growing adoption of microSD. With very few exceptions, it was the memory card format of choice for most manufacturers. Come to think of it, it was an easy win – MMC and SD (and even the short-lived miniSD) were too big and really only Sony was pushing Memory Stick.
The percentage of smartphone manufacturers that have adopted microSD by 2010
microSD, sometimes called “TransFlash”, was launched in 2004. The first phone to use the new card format was certainly a Motorola – there are a few models that came out in 2004, but evidence points to the Motorola E398 being the first.
The E396 was capable of playing MP3s and came with a 64MB card in the box. Even with heavy compression, you couldn’t put a lot of songs in it, but you could always take it out and replace it with a new card.
This phone has an important place in history as it served as the basis for the Motorola ROKR E1 – the first phone with iTunes support. Apple controlled 75% of the digital music sales market in 2005 and that was heavily dependent on the success of the iPod. However, Steve Jobs saw the danger phones posed to his pocket music player and wanted to enter that market as well. The ROKR was a failure, but the phone that followed was, let’s just say, a huge success.
microSD is a smaller version of the SD card. There are some minor differences (other than the size we mean), but they’re so small that a passive adapter can convert from microSD to full-size SD. This was useful for plugging the card into a computer to load songs onto it, or to download photos and videos you’ve taken on your phone.
This relationship meant that the improvements in microSD went hand in hand with the evolution of the SD card. The first big change came in 2006 with the introduction of the SDHC – HC standard for “High Capacity”.
Previously cards were limited to 2GB capacity. SDHC extended this to 32GB and made FAT32 support mandatory. This file system allowed not only large maps, but also large files (up to 4 GB).
The next big leap took place in 2009 with the SDXC format, “eXtended Capacity”. These pushed the limit to 2TB and moved to exFAT, an evolution of the FAT32 file system that allows files to exceed 4GB.
A few years ago, the SD specification was updated with SDUC, “Ultra Capacity”, which supports cards up to 128TB. It will still be a long time before this limit is reached. In fact, even more than a decade, the SDXC format has not yet become a limiting factor, as the largest microSD cards currently on the market have a capacity of 1TB.
The world’s first 1TB microSD card arrived in 2019 for $450
Capacity is the most important metric of a microSD card, but there are a few others you should be aware of. The “speed class” is very important for some applications because it guarantees a minimum sequential write speed. The speed class is usually indicated on the card itself if you know how to read the icons.
The simplest rating is just something like “class 2”, which is marked on the card as a 2 inside a C. This means a guarantee that the card will never drop below 2MB/s There are classes C2, C4, C6 and C10. The faster the card, the faster you can copy files to it.
Some real-time applications like video recording are highly dependent on sustained write speed, so much so that there is a dedicated class. It ranges from V6 to V90, which means 6MB/s (enough for standard definition video) all the way up to 90MB/s (which you need for 8K footage).
Here’s a handy chart from the SD Association that shows 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 Classes required for a given video resolution (and frame rate)
The original SD format called for transfer speeds of up to 12.5MB/s, which was later increased to 25MB/s. The data bus was later upgraded to UHS-I (“Ultra High Speed”), which increased the speed limit to 104 MB/s.
A Complete Overview of SD Speed Classes
UHS-II is a major departure from the original format as it adds an extra row of pins. This further increased the transfer speeds to 156 MB/s in full-duplex mode and 312 MB/s in half-duplex mode (i.e. data flows in both directions or in one direction, respectively ). Putting an extra row of pins on large SD cards was easy enough, however, the size of microSD posed a challenge.
UHS-II microSD cards exist, but they are rare and expensive. Even rarer seem to be devices that support UHS-II microSD cards. Even without UHS-II, the cards are good enough for high resolution video capture, but the rise of smartphones has introduced a new challenge.
More speed requires more pins – enter UHS-II and SD Express
So far we have talked about memory card as storage for multimedia – MP3 and videos. These remain its most popular uses. A more interactive use is to store apps and games, which have grown in size and complexity over time.
They’re not great apps for maps, though, because they’re slow in other ways. Video is recorded sequentially, so only sequential speeds matter. Apps and games require fast random access and most cards just aren’t designed for that.
Some are better than others though – the SD Association introduced the Application Performance Class. Both describe speed in terms of IOPS, random input/output operations per second. The first class is called A1 and guarantees 1500 read IOPS and 500 write IOPS. A few years later came A2, which increased the targets to 4,000 IOPS for reads and 2,000 IOPS for writes.
The latest development is SD Express, which just follows the example of NVMe SSDs and adopts the PCIe data bus. The original specification allowed for a single PCIe 3.0 lane and transfer speeds of up to 985MB/s. Then came support for a single PCIe 4.0 lane (or two PCIe 3.0 lanes) of up to at 1,970 MB/s. The highest speed possible today is achieved with two PCIe 4.0 lanes – a whopping 3,940 MB/s.
SD Express requires additional pins similar to UHS, which hinders adoption on tiny microSD cards. And as we said, devices supporting the extra pins are rare.
The Steam Deck can run games from a microSD card, however, Valve has only equipped it with a UHS-I slot. That means transfer speeds not much faster than a spinning HDD (better seek times, but nowhere near as good as an SSD). The Nintendo Switch also only has a UHS-I slot.
The rise of SD and microSD cards
MicroSD cards are still quite popular, their small form factor has earned them a place in action cameras, drones, and more. And they found use in portable consoles, although larger SD cards (especially the SD Express type) would have been a better choice.
Their popularity on smartphones, however, is declining. How come? We want to partly blame the streaming services – how many MP3s and video files do you have on your phone? And what about your friends? With fast 4G and now faster 5G and falling mobile data costs, streaming has gone from viable to preferred option. Spotify, Netflix, YouTube and more mean you don’t need all that storage on your phone.
Mobile gaming is now bigger than PC and console gaming combined, but that won’t drive microSD adoption for the reasons discussed above. A game large enough to struggle to fit into internal storage will also be too demanding to run on the card.
Another culprit is the growing capacity of the built-in storage. 128GB seems like the average right now and most people say they need 128-256GB. With that, there’s not much need for expandable storage.
We know some of you absolutely hate that most manufacturers have stopped equipping their phones with microSD slots, especially in the flagship class. Unfortunately, the average consumer seems to care as much about the card slot as they do compact phones. The same goes for the average smartphone maker.
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