SD Card Evolution to SD Express: Windows Handheld and PC Compatibility Guide

The short version​

• The SD card was announced in 1999 by SanDisk, Matsushita (now Panasonic) and Toshiba, according to How-To Geek. It arrived as the successor to the MultiMediaCard (MMC), which launched in 1997.
• The SD Association says Panasonic, SanDisk and Toshiba (now KIOXIA) set it up in January 2000 as an industry-wide body to develop and promote card standards. That makes it a later milestone than the 1999 announcement.
• The format has kept growing. The SD Association fact sheet lists a 2GB limit for the original SD, miniSD and microSD standards, 32GB for SDHC, 2TB for SDXC and 128TB for SDUC.
• SD Express adds the PCIe and NVMe interfaces that SSDs use. The SD Association gives its ceiling as 3,940MB/s.
• "Beat every competitor" is rhetorical shorthand. SD is dominant and long-lived, but it is not the only card format ever to survive.

A quick trip through the 1990s​

How-To Geek's timeline starts with flash storage. SanDisk, then called SunDisk, shipped a 20MB flash SSD for IBM laptops in 1991 at roughly $1,000. CompactFlash followed three years later. After that came a crowd of formats: Toshiba's SmartMedia, Sony's Memory Stick and the MMC.

The article attributes each format's downfall to specific causes:

• SmartMedia had no controller and a 128MB ceiling.
• Memory Stick was proprietary and expensive.
• MMC lacked features that SD later added, such as a faster bus, copy protection, a physical write-protect switch and a sturdier body.

Treat these as the author's account, not settled history. Nothing I could verify independently establishes market share or a single cause of failure for any of these formats. Memory Stick's price probably hurt it, but the real story is almost certainly a mix of price, licensing, timing and device support.

Why SD stuck around​

The article gives three reasons for SD's staying power:

1. It was licensed broadly, unlike Sony's proprietary format.
2. It packed a controller into a small card, which let capacities keep growing.
3. It carried built-in copy protection.

The SD Association's own description supports the first point in outline. The association says it does not make or sell products. It exists to create standards used by competing manufacturers who build interoperable cards and devices. Membership is open to anyone, and the group counts about 800 members.

Some caveats apply:

• That is the standards body describing itself. It shows how SD was organised, not that openness alone caused its success.
• "Open" also has limits. The association's FAQ says building SD products involves licence agreements, including separate ones with SD-3C LLC and, for some features, third parties.
• The copy-protection point has aged. The FAQ notes that since 2018 cards can be made without CPRM, under the SD 6.10 specification. That means not every card has it.

SD today: bigger, faster, pickier​

Capacity tiers​

The labels on the packaging map to specification limits. Here is the FAQ's breakdown:

These are ceilings written into the specification, not a list of cards on shelves. The 128TB figure shows where the standard can go. It does not describe what you can buy.

SD Express​

The big recent change is SD Express. The SD Association says SD Express was introduced in the SD 7.0 specification and microSD Express in SD 7.1. SD 8.0 enhanced both, and SD 9.1 added SD Express speed classes plus power and thermal management.

The association's fact sheet describes SD 8.0 as creating SD Express with PCIe Gen 4 x2 lanes. The practical effect is that a card can behave more like a removable SSD than like a classic flash card.

The compatibility fine print​

This is where the rosy retrospective needs a reality check. The SD Association's guidance on bus speeds says any high-speed card can be used in UHS-I, UHS-II or SD Express hosts. To get the full performance, the host and card should both support the faster interface.

The association also describes a more radical option for hardware makers. A host can implement only the PCIe/NVMe interface. Such a host cannot take standard UHS-I cards and is not considered SD-compliant. The association recommends limiting that design to semi-embedded cases, to avoid confusing consumers.

The Switch 2 example: "SD" doesn't mean "any SD"​

Nintendo's support page shows how the same card shape can hide a compatibility trap. The Nintendo Switch 2 works only with microSD Express cards. Other details from that page:

• A regular microSD card previously used in an original Switch will not let the Switch 2 save or load digital games or save data.
• The Switch 2 can load screenshots and videos captured on a regular microSD card.
• The first use of a microSD Express card requires an internet system update, and cards up to 2TB are supported.
• In an original Switch, a microSD Express card runs at the speed of a regular microSD card.

So a long-lived physical form factor does not guarantee interchangeability.

What this means for Windows PCs and handhelds​

The article lists laptops, handheld PCs and mini PCs as common homes for SD and microSD slots. The best verified example I found is MSI's Claw 8 EX AI+, a Windows 11 handheld.

• TechPowerUp's review lists a microSD Express card slot alongside two Thunderbolt 4 ports.
• The same review says the slot is compatible with regular microSD cards.
• MSI's own page claims average read speeds of 600-800MB/s and notes that actual results vary with the card and system.
• TechPowerUp could not test the slot with a microSD Express card. The reviewer said these cards were among the products most heavily hit by memory and storage shortages.
• TechPowerUp says cards top out at about 900MB/s reads and 700MB/s writes. That is an editorial estimate. It sits well below the SD Association's 3,940MB/s standard maximum.

That gap matters. The 3,940MB/s figure is what the interface can do on paper. Cards that actually reach it are a different matter. The handheld above is specified at far lower real-world speeds. Check the card's rated speed, not just the "Express" label.

Meanwhile, some retail listings are vague. B&H's spec table lists the slot as microSD/microSDHC/microSDXC, while the manufacturer and other retailers say microSD Express. If it matters to you, verify against the manufacturer's spec sheet before buying.

Practical buying checklist​

1. Identify your host. Look for "microSD Express" in the device's spec sheet, not just "microSD."
2. Match the card to the slot. A UHS-I or UHS-II card in an Express slot works at the older speed. An Express card in an older slot works, but without Express performance.
3. Check for slot-specific rules. Some devices, like the Switch 2, accept only Express cards for games.
4. Treat headline speeds as ceilings. Look for rated speed classes and independent tests.
5. Expect a price premium. TechPowerUp describes Express cards as unusually expensive during the current storage shortage.

What the retrospective gets right, and where it overreaches​

Well supported:

• SD is a decades-old standard with an unusually wide ecosystem.
• Its capacity and interface specifications have kept advancing.
• SD Express is a real, standards-based path to SSD-like speeds.

Opinion, not measurement:

• Claims that SD is the "most successful" or "most popular" card format are plausible. The SD Association itself calls SD cards the most popular portable storage cards in the world, but that is an industry body's own characterisation. I found no independent market-share data.
• The prediction that smartphones will bring SD slots back because of the memory shortage is speculation.
• "Nothing's come close since" is a headline flourish. Several formats from the era coexisted with SD for years.

Bottom line​

The SD card's real achievement is institutional as much as technical. A broad, licensable standard let many manufacturers build compatible products, and the specification kept evolving through SDHC, SDXC, SDUC and now PCIe-based Express. For PC users the lesson is simple. The slot's shape no longer tells you what it can do. Before you buy a card for a handheld, a laptop or a console, check which interface the host actually supports.