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

The recent shopping frenzy has us looking for great deals on microSD cards, and with it comes the sad fact that many of us no longer own phones with memory expansion slots. Which takes us down memory lane, revisiting the history of the microSD.

We did a memory card review a few years ago, covering MMC, SD, Memory Stick, and more. Today we’re just going to focus on microSD because — for better or worse — this is the card that wins the format wars.

That’s ancient history now, and we had an article from over a decade ago documenting the growing popularity of microSD. With very few exceptions, it is the memory card format of choice for most manufacturers. Looking back, it was an easy win — both 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 some models in 2004, but there is evidence that the Motorola E398 was the This first.

The E396 is capable of playing MP3s and comes with a 64MB card in the box. You can’t fit many songs in it, even with heavy compression, but you can always pop it out and replace it with 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 for Motorola’s ROKR E1 – the first phone to support iTunes. Apple controlled 75 percent of digital music sales in 2005, largely due to the success of the iPod. However, Steve Jobs saw the danger cell phones posed to his pocket music players and wanted to enter that market as well. ROKR was a flop, but arguably the subsequent 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 (we’re not referring to 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 or download photos and videos you’ve taken on your phone.

This relationship means that improvements to the microSD have been made in tandem with the development of SD cards. The first major change came in 2006 with the introduction of the SDHC (HC for “High Capacity”) standard.

Previously, cards were capped at 2GB. SDHC expands this to 32GB and mandates support for FAT32. The file system supports not only large cards, but also large files (up to 4GB).

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

The next leap forward came in 2009 with the SDXC format “extended capacity”. These raised the limit to 2TB and switched to exFAT, an evolution of the FAT32 file system that allowed files to grow beyond 4GB.

A few years ago, the SD specification was updated to SDUC, or “Ultra Large Capacity,” which supports cards up to 128TB. It will take a long, long time to reach that limit. In fact, even the ten-plus-year-old SDXC format hasn’t been a limiting factor yet, as the largest microSD card currently on the market has a capacity of 1TB.

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

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 like a “Grade 2”, marked as a 2 inside a C on the card. This means guaranteed cards will never drop below 2MB/s. There are C2, C4, C6 and C10 categories. 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) depend so much on sustained write speed that there is a dedicated class for it. It goes from V6 to V90, which means from 6MB/s (enough for standard definition video) all the way up to 90MB/s (you’ll need 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 a guide, as different cameras use different codecs at different bandwidths.

SD speed class required for a given video resolution (and frame rate)

SD speed class required for a given video resolution (and frame rate)

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

Complete overview of SD speed grades

Complete overview of SD speed grades

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

UHS-II microSD cards do exist, but they are rare and expensive. Even rarer appear to be devices that actually 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.

Faster Speeds Need More Pins - Enter UHS-II and SD Express
Faster Speeds Need More Pins – Enter UHS-II and SD Express

So far, we’ve discussed memory cards as storage for multimedia — MP3s and videos. These are still its most popular uses. A more interactive use is to store applications and games that can grow in size and complexity over time.

However, none of these are good applications for cards, as they are slow on the other hand. Videos are recorded sequentially, so only sequence speed matters. Applications and games require fast random access, and most cards are not designed for this.

Some are better than others – the SD Association introduced Application Performance Classes. Both describe speed in terms of IOPS (random input/output operations per second). The first class is called A1 and it guarantees 1,500 IOPS read and 500 IOPS write. A few years later came the A2, which increased 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 specification allowed for a single PCIe 3.0 lane and transfer speeds of up to 985MB/s. Then there’s support for a single PCIe 4.0 lane (or two PCIe 3.0 lanes) at speeds up to 1,970MB/s. The highest speed currently possible is achieved through two PCIe 4.0 lanes — up to 3,940MB/s.

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

The Steam Deck can run games from a microSD card, but Valve has only equipped it with a UHS-I slot. That means transfer speeds aren’t much higher 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

The rise of SD and microSD cards

microSD cards are still quite popular, and their small form factor has earned them a place in action cameras, drones, and more. They’ve found use in handheld game consoles, even though a larger SD card (especially 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 place some of the blame on streaming services — how many MP3 and video files do you have on your phone? what about your friends? With fast 4G and now even faster 5G and falling mobile data costs, streaming has gone from viable to preferred. Spotify, Netflix, YouTube and more mean you don’t need all the storage on your phone.

Mobile gaming is now bigger than PC and console gaming combined, but for the reasons mentioned above, this will not promote microSD adoption. A game that’s too big to fit on the internal storage won’t work on the card either.

Another culprit is the increase in built-in storage capacity. 128GB seems to be the current average, with most people saying they need 128-256GB. This way you don’t need much expandable storage.

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

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

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