microSD Card for Steam Deck, ROG Xbox Ally & Legion Go: UHS-I, UHS-II or Express? (2026 Buying Guide)

A gaming handheld fills up fast: plenty of current games need more than 100 GB on their own. The easiest upgrade is a microSD card, no screwdriver required. But the card slots aren't all the same. The Steam Deck has a UHS-I slot, the ROG Xbox Ally and Ally X a faster UHS-II slot, and the new ROG Xbox Ally X20 even uses microSD Express. Buy the wrong card and you pay for speed your handheld can't use. This guide shows which card type suits your device, what A2, U3 and V30 mean, and which five cards are worth a look.

Transparency: We haven't tested these cards ourselves. The card slot details come from the official spec sheets by Valve, ASUS, Lenovo and MSI, the standards from the SD Association, and the card specs from the manufacturers and the checked Amazon.de pages (as of November 2026). We don't list prices because they change all the time.

Which card slot does your handheld have?

Lenovo's and MSI's official spec sheets don't state the interface. Check your model's manual before paying extra for UHS-II. A good UHS-I card is the safe choice, because it works in every one of these slots.

UHS-I, UHS-II and microSD Express in a nutshell

All three card types are the same size. The difference lies in the contacts and the maximum speed of the interface. The SD Association's figures:

What that means for you:

• UHS-I slot (Steam Deck): It can't go beyond UHS-I speed. An expensive UHS-II or Express card brings no benefit here.
• "Up to 200 MB/s" on UHS-I cards: Many cards advertise more than 104 MB/s. SanDisk itself says this relies on its own technology and needs a compatible device. ASUS names the ROG Ally X and newer models as devices that can use such "overclocked" cards.
• UHS-II slot (ROG Xbox Ally/Ally X): A real UHS-II card with a second row of contacts is worth it here if you want faster load times. UHS-I cards still work.
• microSD Express slot (ROG Xbox Ally X20): According to ASUS, UHS-II cards only run at UHS-I speed in it. For full speed you need a microSD Express card.
• Express card in an older slot: microSD Express cards keep the UHS-I interface. They work in UHS-I and UHS-II slots, but only in UHS-I mode.

A1, A2, U3, V30: what matters for gaming?

Cards carry lots of labels. Only a few matter for games:

• A1 / A2 (Application Performance Class): Minimum figures for lots of small accesses. A1 requires 1,500 read and 500 write operations per second (IOPS), A2 4,000 and 2,000, both with at least 10 MB/s sustained. According to the SD Association, you only get A2 performance when both the card and the device support A2. None of the handheld makers above lists A2 support in their spec sheets.
• U3 / V30 / V60: These are guaranteed minimum write speeds for video recording. ASUS points out that game load times depend mostly on read speed. So you don't need to hunt for V60 or V90 for gaming.
• SDXC: Cards above 32 GB up to 2 TB. Valve lists SD, SDHC and SDXC for the Steam Deck. Larger SDUC cards above 2 TB aren't included. ASUS names 2 TB as the maximum capacity for all current Ally models.

How much capacity?

For the Ally line, ASUS recommends at least 512 GB to 2 TB and considers 256 GB tight, because many AAA games exceed 100 GB on their own. As a rough guide:

• 256 GB: for indie and retro games or a few smaller titles.
• 512 GB: a good middle ground for a mixed library.
• 1 TB to 2 TB: if you want several big games with you without constantly deleting.

According to ASUS, a larger internal SSD also gives you more space and more speed. A microSD card, on the other hand, is ready to go without opening the device. If you'd rather use a USB SSD on the dock, see the portable SSD buying guide.

Setting up the card: Steam Deck and Windows handhelds

Steam Deck (SteamOS)

The Steam Deck uses the ext4 file system with casefolding for microSD cards and formats the card itself. Insert the card, press the Steam button, open Settings, then System and Format SD Card. On newer SteamOS versions this takes you to the Storage menu, where you confirm the format. After that, you choose for every installation whether the game goes to internal storage or the card. According to Valve, the Deck can even boot from a microSD card.

ROG Xbox Ally and other Windows handhelds

ASUS recommends formatting the card as NTFS: in Windows Settings under System > Storage > Advanced storage settings > Disks & volumes. This erases all data on the card. Then create a folder on the card in each launcher, in Steam for example under Settings > Downloads > Steam Library Folders. The Xbox app, Battle.net, Epic, the EA app, Ubisoft Connect and GOG Galaxy ask for the install location during installation.

Because the Steam Deck uses ext4 and Windows handhelds use NTFS, you'll usually reformat the card when moving it between them. Back up anything you want to keep first.

Five cards that fit

The cards below aren't test winners but examples for the different card slots. All figures come from the manufacturer or the checked Amazon.de page. All five were sold and shipped by Amazon when we checked.

Example model

For any handheld: Samsung T7 microSD, 512 GB

Samsung's microSD line for gaming handhelds. According to the Amazon page, Samsung explicitly names the Steam Deck and ROG Ally.

Capacity

512 GB (also 128 GB, 256 GB and 1 TB)

Interface

UHS-I, U3

Read

up to 170 MB/s

Protection

waterproof, temperature-proof, X-ray-proof, magnet-proof, drop-proof

Warranty

3 years (limited)

Model

MB-MB512T/WW

Right for you if you want a solid UHS-I card for the Steam Deck or a handheld without a clear UHS-II spec.

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Example model

Lots of space with A2: SanDisk Extreme microSDXC, 1 TB

A classic for cameras and smartphones that also works in any handheld slot.

Capacity

1 TB (also smaller sizes)

Interface

UHS-I, U3

Classes

A2, V30, Class 10

Read

up to 190 MB/s (manufacturer figure above the UHS-I standard)

Model

SDSQXAV-1T00-GN6MA

Right for you if you want plenty of space for the Steam Deck. By the standard, its UHS-I slot can't use speeds above 104 MB/s.

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Example model

Officially licensed for the Ally: SanDisk microSD for ROG Xbox Ally (X), 1 TB

According to SanDisk, this card is officially Xbox licensed and designed for the ROG Xbox Ally and Ally X.

Capacity

1 TB (also 512 GB and 2 TB)

Read / write

up to 200 / 140 MB/s (above 104 MB/s only with a compatible device)

Compatibility per SanDisk

ROG Xbox Ally, ROG Xbox Ally X, Windows 10/11

Warranty

Lifetime Limited (30 years in Germany)

Model

SDSQXKN-1T00-GN6GN

Right for you if you own a ROG Xbox Ally or Ally X and want a card that's explicitly approved for it.

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Example model

Real UHS-II: Lexar GOLD microSDXC UHS-II, 256 GB

A card with a second row of contacts for handhelds with a UHS-II slot. Lexar explicitly mentions UHS-II-compatible gaming devices.

Capacity

256 GB (also 128 GB)

Interface

UHS-II

Read / write

up to 280 / 180 MB/s

Classes

V60, U3, Class 10

Right for you if you own a ROG Ally, Ally X, ROG Xbox Ally or Ally X and want to use the faster UHS-II. At 256 GB it's better suited to a smaller game selection. In the Steam Deck it only runs at UHS-I speed.

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Example model

For the ROG Xbox Ally X20: Samsung P9 Express, 512 GB

A microSD Express card for devices with an Express slot, such as the ROG Xbox Ally X20 or the Switch 2.

Capacity

512 GB (also 256 GB)

Interface

PCIe Gen 3.0 x1, NVMe 1.3, SD 7.1

Read

up to 800 MB/s (SD Express), 90 MB/s (UHS-I)

Classes

Class 10, U3, V30, A1

Warranty

3 years (limited)

Model

MB-MK512T/WW

Right for you if you own a ROG Xbox Ally X20. In UHS-I and UHS-II slots it falls back to UHS-I speed, so it isn't worth it there. More on Express cards in the Switch 2 microSD guide.

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The cards compared

Card	Type	Capacity	Read (manufacturer)	Best for
Samsung T7	UHS-I	512 GB	170 MB/s	Steam Deck, all handhelds
SanDisk Extreme	UHS-I, A2	1 TB	190 MB/s	lots of space, all handhelds
SanDisk for ROG Xbox Ally	UHS-I	1 TB	200 MB/s	ROG Xbox Ally / Ally X
Lexar GOLD	UHS-II	256 GB	280 MB/s	handhelds with a UHS-II slot
Samsung P9 Express	microSD Express	512 GB	800 MB/s	ROG Xbox Ally X20

Checklist before you buy

1. Which slot does your handheld have according to the manufacturer: UHS-I, UHS-II or Express?
2. Are you only paying for speed your slot can actually use?
3. Is the capacity enough for your big games (often more than 100 GB per title)?
4. SDXC up to 2 TB rather than SDUC?
5. A well-known brand and a reputable seller to avoid fakes?
6. Important data backed up before you format?

Playing on the TV? You'll find docks for the Steam Deck and other handhelds in the Steam Deck dock buying guide. The right power adapter is covered in the charger buying guide, and power on the go in the power bank buying guide.

FAQ

Is a UHS-II card worth it for the Steam Deck?

No. Valve lists a UHS-I slot for the Steam Deck. A UHS-II card only runs in UHS-I mode there.

Which file system does the card need?

On the Steam Deck, ext4 with casefolding, and the Deck formats the card itself. For the ROG Ally line, ASUS recommends NTFS.

How big can the card be?

ASUS names 2 TB as the maximum for all current Ally models. Valve lists SD, SDHC and SDXC for the Steam Deck, which means cards up to 2 TB.

Does a microSD Express card work in the Steam Deck?

Yes, but only in UHS-I mode. Samsung lists up to 90 MB/s read speed for the P9 Express in that mode.

What does "up to 200 MB/s" mean on a UHS-I card?

It's a manufacturer figure above the UHS-I standard of 104 MB/s. According to SanDisk, it needs a compatible device. ASUS names the ROG Ally X and newer models as such devices.

Does A2 matter?

Only if the device supports A2 as well. The handheld makers don't mention it in their spec sheets.

Sources

As of November 2026.

• Valve: Steam Deck – Tech Specs
• Valve: Steam Deck FAQ (file system, booting from microSD)
• Valve SteamOS on GitHub: formatting the SD card from SteamOS 3.6
• ASUS ROG: How to Install Games to an SD Card on your ROG Ally or ROG Xbox Ally
• ASUS ROG: ROG Xbox Ally X (2025) – Tech Specs
• Lenovo PSREF: Legion Go 2 (8ASP2)
• Lenovo PSREF: Legion Go S (8APU1)
• MSI: Claw 8 AI+ – Specifications
• SD Association: Bus Speed (UHS-I, UHS-II, SD Express)
• SD Association: Application Performance Class (A1/A2)
• SD Association: Capacity SD, SDHC, SDXC, SDUC
• SD Association: SD Express and microSD Express white paper
• SanDisk: microSD Card for ROG Xbox Ally (X)
• Samsung P9 Express: data sheet

Manufacturers occasionally change specs and variants. If anything important changes, we'll update this article.