Our recent shopping spree got us looking for great deals on microSD cards, and with that came the sad realization that many of us no longer have a phone with a memory expansion slot. This sent us on a trip down memory lane to revisit the history of the microSD.
A few years ago we did a memory card retrospective, which included MMC, SD, Memory Stick and the like. Today we want to focus exclusively on microSD because – for better or for worse – this is the card that won the format wars.
That’s old story now, we have an article from over a decade ago chronicling the increasing adoption of microSD. With very few exceptions, it has been the memory card format of choice for most manufacturers. In hindsight it was an easy win – MMC and SD (and even the short-lived miniSD) were too big and really only Sony was pushing for Memory Stick.
The percentage of smartphone manufacturers that have adopted microSD by 2010
microSD, sometimes referred to as “TransFlash”, was launched in 2004. The first phone to use the new card format was certainly a Motorola – there are a few models released in 2004 but there is evidence that it is the Motorola E398 the First.
The E396 could play MP3 files and came with a 64MB card. Even with heavy compression, not many songs could fit on 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 had a controlling 75% market share of digital music sales in 2005, and that depended heavily on the success of the iPod. However, Steve Jobs saw the danger that phones posed to his pocket music player and wanted to enter this market as well. The ROKR was a failure, but the phone that followed was, shall we say, a huge success.
microSD is a smaller version of the SD card. There are some minor differences (besides the size, which we mean), but they’re small enough that a passive adapter can convert from microSD to full-size SD. This was useful for connecting the card to a computer to load it with songs or to download the photos and videos you took on your phone.
This relationship meant that microSD improvements have kept pace with the development of the SD card. The first big change came in 2006 with the introduction of the SDHC – HC for “High Capacity” – standards.
Previously, cards were limited to 2GB capacity. SDHC expanded that 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 came in 2009 with the SDXC format “eXtended Capacity”. They have increased the limit to 2TB and switched to exFAT, an evolution of the FAT32 file system that allows files to grow beyond 4GB.
A few years ago, the SD specification was updated with SDUC, “Ultra Capacity”, which supports cards up to 128TB. It will be a long time before this limit is reached. In fact, even the decades-old SDXC format has yet to 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 was released in 2019 with a price tag of $450
Capacity is the most important measure of a microSD card, but there are a few others to consider. The “Speed Class” is very important for some applications as it guarantees a minimum sequential write speed. The speed class is usually written on the card itself if you know how to read the symbols.
The simplest classification is something like “Class 2,” which is marked on the map as a 2 in a C. This means a guarantee that the card will never drop below 2 MB/s. There are C2, C4, C6 and C10 classes. The faster the card, the faster you can copy files to it.
Some real-time applications like video recording rely heavily on sustained write speed, so much so that it has its own class. It goes from V6 to V90, so from 6MB/s (enough for standard definition video) to 90MB/s (what you need 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 just a guide as different cameras use different codecs at different bandwidths.
Required SD speed classes for a given video resolution (and frame rate)
The original SD format was intended for transfer speeds of up to 12.5 MB/s, later increased to 25 MB/s. The data bus has been further upgraded with UHS-I (“Ultra High Speed”), increasing the speed limit to 104 MB/s.
A complete overview of the SD speed classes
UHS-II is a big departure from the original format as it adds an extra row of pens. This allowed the transmission speeds to be further increased to 156 MB/s in full-duplex mode and 312 MB/s in half-duplex mode (ie data flow in both directions or only one direction). Adding an extra row of pins to the large SD cards was easy enough, but the size of microSD presented a challenge.
UHS-II microSD cards exist, but they’re rare and expensive. Devices that actually support UHS-II microSD cards seem to be even rarer. Even without UHS-II, the cards are good enough for high-resolution video recording, but the rise of smartphones brought a new challenge.
More speed requires more pins – enter UHS-II and SD Express
So far we have talked about the memory card as a storage for multimedia – MP3s and videos. These remain the most popular applications. A more interactive use is to store apps and games that have grown in size and complexity over time.
However, these are not good uses for the cards as they are slow in other ways. Videos are recorded sequentially, so only sequential speeds matter. Apps and games need fast random access, and most cards just aren’t designed for that.
However, some are better than others – 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 1,500 IOPS for reads and 500 IOPS for writes. 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 NVMe SSDs and adopts the PCIe data bus. The original specification allowed a single PCIe 3.0 lane and transfer speeds of up to 985 MB/s. Then came support for a single PCIe 4.0 lane (or two PCIe 3.0 lanes) at up to 1,970 MB/s. The currently highest possible speed is achieved with two PCIe 4.0 lanes – a whopping 3,940 MB/s.
SD Express requires the extra pins similar to UHS, which hampers acceptance on the tiny microSD cards. And as said, devices that support the extra pins are rare.
The Steam Deck can run games from a microSD card, but Valve only equipped it with a UHS-I slot. This means transfer speeds that aren’t much faster than a spinning hard drive (better seek times, but nowhere near as good as an SSD). The Nintendo Switch also only has one UHS-I slot.
The rise of SD and microSD cards
microSD cards are still quite popular, their tiny form factor has earned them a place in action cameras, drones and so on. And they’ve found use in handheld consoles, although the larger SD cards (especially the SD Express kind) would have been a better choice.
However, their popularity on smartphones is declining. Where from? We’ll put some blame on streaming services – how many MP3s and video files do you have on your phone? what about your friends With fast 4G and now faster 5G, and mobile data costs falling, streaming has gone from being a viable option to a preferred option. Spotify, Netflix, YouTube and the like mean you don’t need all that storage space on your phone.
Mobile gaming is now bigger than PC and console gaming combined, but that won’t encourage microSD adoption for the reasons outlined above. A game big enough to have internal storage issues is also too demanding for the card to run.
Another culprit is the increasing capacity of the built-in memory. 128GB seems to be the average at the moment and most people say they need 128-256GB. This means that no expandable memory is required.
We know some of you absolutely hate that most manufacturers stop adding microSD slots to their phones, especially in the flagship tier. Unfortunately, the average consumer seems to care about the card slot just as much as they do about compact phones. The same is true for the average smartphone manufacturer.