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UHS on an SD memory card refers to its Ultra High Speed bus interface, while U1 and U3 are separate speed-class marks for minimum write performance. To choose a card, check both the interface and the card’s speed-class marking against your device manual and intended use; a higher UHS generation does not guarantee a particular real-world transfer rate.
What does UHS mean on an SD card?
UHS stands for Ultra High Speed. The SD Association uses the term for bus interfaces that connect an SD card to a host device. Its interface generations are UHS-I, UHS-II and UHS-III. These labels describe the interface, not the card’s minimum write-speed class.
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The interface rate is a bus ceiling, not a promise of the speed a particular card will achieve. The SD Association notes: “Maximum speed differs from the bus I/F speed. It varies depending upon the card performance.” Card performance, the host device and the operation being performed all affect actual results. See the Association’s bus-speed overview.
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How do UHS-I, UHS-II and UHS-III differ?
The Roman numeral identifies the bus-interface generation. The SD Association lists the following interface rates; these are standards figures, not measured typical speeds for a specific retail card.
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- Save time with card offload speeds of up to 200MB/s powered by SanDisk QuickFlow Technology (Up to 200MB/s read speeds, engineered with proprietary technology to reach speeds beyond UHS-I 104MB/s, require compatible devices capable of reaching such speeds. Based on internal testing; performance may be lower depending upon host device, interface, usage conditions and other factors. 1MB=1,000,000 bytes. X = 150KB/sec. SanDisk QuickFlow Technology is only available for 64GB, 128GB, 256GB, 512GB and 1TB capacities. 1GB=1,000,000,000 bytes. 1TB=1,000,000,000,000 bytes. Actual user storage less.)
- Pair with the SanDisk Professional PRO-READER SD and microSD to achieve maximum speeds (sold separately)
- Shot speeds up to 90MB/s (Write speed up to 90MB/s. Based on internal testing; performance may be lower depending upon host device. 1MB=1,000,000 bytes. X = 150KB/sec.)
- Perfect for shooting 4K UHD video and sequential burst mode photography (Full HD (1920x1080) and 4K UHD (3840 x 2160) video support may vary based upon host device, file attributes and other factors. See HD page on SanDisk site.)
- UHS Speed Class 3 (U3) and Video Speed Class 30 (V30) (UHS Speed Class 3 designates a performance option designed to support 4K UHD video recording with enabled UHS host devices. UHS Video Speed Class 30 (V30), sustained video capture rate of 30MB/s, designates a performance option designed to support real-time video recording with UHS enabled host devices. See the SD Association’s official website.)
| Interface | Listed bus rates |
|---|---|
| UHS-I | 50 MB/s for SDR50 or DDR50; 104 MB/s for SDR104 |
| UHS-II | 156 MB/s full duplex or 312 MB/s half duplex |
| UHS-III | 312 MB/s full duplex or 624 MB/s full duplex |
The figures describe different interface modes, so they should not be read as guaranteed card write speeds. For the mode definitions and qualifications, consult the SD Association’s bus-speed overview.
What do U1 and U3 mean?
U1 and U3 are UHS Speed Class marks. They indicate minimum write speeds, not interface generations:
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- CAPTURE LARGER THAN LIFE. Unlock 4K UHD(3) brilliance and pristine high res stills with video speed class ratings of U3 and V30(4).
- SPEED BARRIERS SHATTERED. Save precious moments with blazing read speeds up to 250MB/s(2) and write speeds up to 170MB/s(2) [256GB-1TB capacities(1)].
- MAXIMIZE WITH MASSIVE CAPACITY. Capture for longer and store more with up to 2TB(1) of storage that can hold up to 2,808 minutes of 4K UHD video recorded at 30 fps (641MB/minute)(9).
- DEFY THE ELEMENTS. Unrelentingly resilient, Sandisk SD memory cards are engineered to perform in extreme conditions, despite rough handling and constant use.(6)
- CONTENT MANAGEMENT, SIMPLIFIED. Back up, organize, and transfer everything easily with the Sandisk Memory Zone desktop app,(7) whether you use an SD card slot or a card reader.
- U1: minimum write speed of 10 MB/s.
- U3: minimum write speed of 30 MB/s.
The SD Association says these marks can apply to UHS-I, UHS-II and UHS-III product families. A card can therefore have both an interface label and a U1 or U3 mark. Read the two as separate pieces of information. Details are in the Association’s Speed Class overview.
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For video, speed-class marks indicate minimum sequential access performance under defined conditions. The appropriate mark depends on the recording device and recording conditions; a mark alone does not guarantee a particular resolution or recording mode.
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- CAPTURE LARGER THAN LIFE. Unlock 4K UHD(3) brilliance and pristine high res stills with video speed class ratings of U3 and V30(4).
- SPEED BARRIERS SHATTERED. Save precious moments with blazing read speeds up to 250MB/s(2) and write speeds up to 170MB/s(2) [256GB-1TB capacities(1)].
- MAXIMIZE WITH MASSIVE CAPACITY. Capture for longer and store more with up to 2TB(1) of storage that can hold up to 2,808 minutes of 4K UHD video recorded at 30 fps (641MB/minute)(9).
- DEFY THE ELEMENTS. Unrelentingly resilient, Sandisk SD memory cards are engineered to perform in extreme conditions, despite rough handling and constant use.(6)
- CONTENT MANAGEMENT, SIMPLIFIED. Back up, organize, and transfer everything easily with the Sandisk Memory Zone desktop app,(7) whether you use an SD card slot or a card reader.
The SD Association’s guidance lists V30 among the marks available in UHS-I mode, and V30, V60 and V90 among the options for UHS-II and UHS-III modes. These V marks are distinct from U1 and U3. Check the camera or recorder manual for the required class and supported recording formats rather than inferring a resolution from the interface label. See the Association’s Speed Class guidance.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to check whether a UHS SD memory card will work
- Check the device’s supported interface. Look in the device manual for UHS-I, UHS-II or UHS-III support. The SD Association says a host performs best when paired with a card supporting at least the host’s interface. A newer card’s bus capability does not make an older host support that interface.
- Confirm card format and capacity. Check the manual for supported SD format and capacity. SDHC, SDXC and SDUC are capacity standards, a separate compatibility question from UHS interface generation.
- Match the speed-class mark to the workload. For sustained video recording, use the class required by the device and recording mode. For other tasks, consider the device’s stated requirements and the card’s class rather than assuming the bus maximum is its write speed.
- Verify the exact recording requirements. Use the manual’s specifications for format, capacity and speed class; the required performance can depend on device and recording conditions.
The Association’s guidance on matching cards and devices explains the host/card interface relationship. Confirm the supported formats and recording requirements in the manual for your specific device.
Quick Recap
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- Great choice for compact to mid-range point-and-shoot cameras
- Quick transfer speeds up to 140MB/s (Up to 140MB/s read speed engineered with proprietary technology to reach speeds beyond UHS-I 104MB/s, requires compatible devices capable of reaching such speeds. Based on internal testing; performance may be lower depending on host device, interface, usage conditions and other factors. 1MB=1,000,000 bytes.)
- Up to 128GB to store tons of pictures (1GB=1,000,000,000 bytes. Actual user storage less.)
- Exceptional video recording performance with UHS Speed Class 1 (U1) Class 10 rating for Full HD video (1080p) (UHS Speed Class 1 (U1) designates a performance option designed to support real time video recording with UHS enabled host devices. See consumers speed page on SanDisk site. Full HD (1920x1080) video support may vary based upon host device, file attributes, and other factors. Visit the SanDisk Video Knowledge Base for more information.)
- Compatible with SanDisk SD UHS-I card reader (sold separately)
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- CAPTURE LARGER THAN LIFE. Unlock 4K UHD(3) brilliance and pristine high res stills with video speed class ratings of U3 and V30(4).
- SPEED BARRIERS SHATTERED. Save precious moments with blazing read speeds up to 250MB/s(2) and write speeds up to 170MB/s(2) [256GB-1TB capacities(1)].
- MAXIMIZE WITH MASSIVE CAPACITY. Capture for longer and store more with up to 2TB(1) of storage that can hold up to 2,808 minutes of 4K UHD video recorded at 30 fps (641MB/minute)(9).
- DEFY THE ELEMENTS. Unrelentingly resilient, Sandisk SD memory cards are engineered to perform in extreme conditions, despite rough handling and constant use.(6)
- CONTENT MANAGEMENT, SIMPLIFIED. Back up, organize, and transfer everything easily with the Sandisk Memory Zone desktop app,(7) whether you use an SD card slot or a card reader.
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