UHS-III, A2 and LV/LVS describe different parts of an SD card system—not competing versions of the same speed rating. UHS-III identifies the bus interface (up to 624 MB/s theoretically), A2 identifies application-oriented performance (4,000 random-read IOPS, 2,000 random-write IOPS and 10 MB/s sustained sequential performance under SD-defined conditions), and LV/LVS identifies low-voltage signaling and host compatibility.
Evaluate them independently: interface, workload performance and electrical signaling. A card can be A2 without UHS-III, while an LV card may work in an older 3.3 V host without using its newest low-voltage mode.
The three labels at a glance
| Label | What it describes | What it does not guarantee |
|---|---|---|
| UHS-III | High-speed SD bus interface; up to 624 MB/s theoretical bus throughput | A 624 MB/s file copy or a particular card’s sustained write speed |
| A2 | Application Performance Class 2 for random I/O and sustained performance | Full A2 behavior in a host that lacks A2 support |
| LV/LVS | 1.8 V/3.3 V signaling and identification between card and host | A replacement for UHS speed classes or a promise of faster storage |
The SD Association documents these as separate capabilities: UHS bus interfaces, Application Performance Class and Low Voltage Signaling.
UHS-III: the bus interface
What the number means
UHS means Ultra High Speed. The SD Association lists theoretical interface ceilings of up to 104 MB/s for UHS-I, 312 or 324 MB/s depending on the terminology used for UHS-II, and 624 MB/s for UHS-III. These are bus capabilities, not minimum transfer rates for every card.
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- Pair with the SanDisk Professional PRO-READER SD and microSD to achieve maximum speeds (sold separately)
- Shot speeds up to 140MB/s (Write speed up to 140MB/s. 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.)
- 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.)
Actual results depend on the card controller and flash, host implementation, protocol mode, reader, file system, workload, temperature and available free space. A UHS-III card cannot make a UHS-I camera or reader operate at UHS-III speed; the link normally falls back to the fastest mode supported by both sides.
Contacts and LVDS
UHS-II and UHS-III use a second row of contacts for their high-speed interface. That interface uses Low Voltage Differential Signaling (LVDS), with two lanes capable of full-duplex traffic—one direction from host to card and the other from card to host.
LVDS is not the same term as LVS. LVDS names the differential signaling technology of the high-speed contact interface. LVS means Low Voltage Signaling, an SD Specification 6.0 feature that governs 1.8 V/3.3 V operating modes and voltage identification.
UHS-III versus U3
These labels are easy to confuse but measure different things:
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- UHS-III: bus-interface generation and theoretical interface bandwidth.
- U3: UHS Speed Class 3, a minimum 30 MB/s sequential-write class under defined conditions.
U1 and U3 speed classes can appear on products using UHS-I, UHS-II or UHS-III. For video, use the camera’s required UHS Speed Class or Video Speed Class rather than assuming a UHS-III logo is sufficient. See the SD Association’s Speed Class overview.
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- 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)
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A2: application performance, not a bus generation
What A2 guarantees
Application Performance Class 2 (A2) specifies these minimums under SD-defined measurement conditions:
- 4,000 random-read IOPS
- 2,000 random-write IOPS
- 10 MB/s sustained sequential performance
A2 also depends on features such as command queuing, cache and maintenance or self-maintenance functions. The class is intended for application workloads, including apps stored on supported Android adopted/adoptable storage.
Host support is required
Full A2 operation is a card-and-host combination. The host must implement the relevant A2 functions; an A2 logo on the card alone cannot add command queuing or cache support to a phone, camera, console or reader. An A2 card remains usable in an A1-compatible context, but the device may not exploit its A2-specific capabilities.
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A2 is not a video rating
Large, continuous video files need reliable sustained sequential writing. A2 primarily characterizes random application I/O. For cameras, drones and action cameras, check the manufacturer’s required UHS Speed Class, Video Speed Class, capacity and file-system support. The SD Association’s video-speed guidance covers classes such as U3, V30, V60 and V90.
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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.)
LV/LVS: electrical signaling and compatibility
How low-voltage signaling works
SD Specification 6.0 introduced Low Voltage Signaling. A compatible card and host identify whether to operate with 3.3 V or 1.8 V signaling, rather than assuming a single voltage at startup.
| LVS type | Associated interface tier |
|---|---|
| LV50 | 50 MB/s UHS-I card |
| LV104 | 104 MB/s UHS-I card |
| LV156 | 156 MB/s UHS-II card |
| LV624 | 624 MB/s UHS-III card |
Those figures associate the LV type with an interface tier; they are not universal file-copy guarantees.
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The two-sided compatibility rule
- An LVS card is designed to remain compatible with conventional 3.3 V hosts. In a legacy host it may simply operate without the newest low-voltage mode.
- An LVS-only host may require a corresponding LV-marked card. Do not assume every conventional card is electrically acceptable.
- An LV symbol on the host or card is the practical indication that this pairing matters.
See the consumer explanation of Low Voltage Signaling compatibility.
Compatibility matrix
| Combination | Likely result | Important limitation |
|---|---|---|
| Legacy 3.3 V host + LVS card | Designed to work | Runs at the host’s supported mode, not necessarily the newest LV mode |
| LVS host + LVS card | Intended pairing | Both still need the same physical form factor and supported bus |
| LVS-only host + conventional card | May fail initialization | Follow the host designer’s approved-card requirements |
| UHS-III card + UHS-I host | Usually falls back to UHS-I | Card cannot upgrade the host interface |
| A2 card + non-A2 host | Card is usable | A2 command queuing/cache benefits may be unavailable |
| UHS-III card + UHS-I reader | Transfer is limited to the reader’s mode | The complete card-reader-computer path must support the target interface |
Choose by workload
Android phones and app storage
- Confirm that the phone accepts a microSD card.
- Check whether its software supports adopted/adoptable storage.
- Look for explicit A2 host support if apps will run from the card.
- Then prioritize capacity, endurance and the phone’s video requirement.
An A2 card is sensible for app-oriented use, but controller limits, encryption, firmware and the operating system can dominate responsiveness.
Action cameras, drones and 4K recording
Follow the device manual’s sustained-write requirement, usually expressed as U3, V30, V60 or V90. A2 may be present, but it does not substitute for a video class.
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- Fast for better pictures and Full HD video. Full HD (1920x1080) video support may vary based upon host device, file attributes, and other factors
- Great choice for compact to mid-range point-and-shoot cameras
- From 32GB to 256GB(1) to store tons of pictures and even more Full HD video(2). (1)1GB=1,000,000,000 bytes Actual user storage less
- Exceptional video recording performance with UHS Speed Class 1 (U1)(5) and Class 10 rating for Full HD video (1080p)(2). (5)UHS Speed Class 1 (U1) designates a performance option to support real time video recording with UHS enabled host devices
- Quick transfer speeds up to 100MB/s. Up to 100MB/s[64GB-256GB; 90MB/s for 32GB] read speed; write speed lower Based on internal testing; performance may be lower depending on host device, usage conditions, and other factors 1MB=1,000,000 bytes
Professional cameras and fast transfers
Verify the camera, card and reader all support the same UHS-II, UHS-III or SD Express path. UHS-III availability is market-dependent; many professional products are UHS-II, while newer high-performance designs may use SD Express.
Embedded designs
- Check contact configuration and supported bus mode.
- Verify whether startup accepts 3.3 V, 1.8 V or requires LVS identification.
- Implement any required A2 command-queuing, cache and maintenance functions.
- Validate power sequencing, signal integrity and fallback with legacy cards.
- Test the exact card families intended for certification and production.
General storage
Capacity, endurance, reliability, file-system compatibility and the host’s supported bus often matter more than A2 or UHS-III markings.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Current market context
The standards remain current vocabulary, but visible consumer availability is uneven. A2 UHS-I cards are common, UHS-II is prominent in professional photography, and specific UHS-III products should be verified individually rather than assumed from a listing’s headline speed. SD Express is the newer PCIe/NVMe-based path and can offer higher theoretical throughput, but it requires an SD Express-capable card, host and reader. The SD Association’s current bus overview and whitepapers describe the distinction.
Examples of cards you may encounter
| Product family | Interface and markings | Typical fit | Limitation |
|---|---|---|---|
| Lexar Professional 1066x Silver | UHS-I, A2, U3, V30; advertised up to 160 MB/s read and 130 MB/s write depending on model and conditions | Phones, drones and action cameras | Not UHS-III or SD Express |
| Lexar FLY | UHS-I, A2, U3, V30 | Android and general mobile use | Not a professional high-end bus |
| Lexar E-Series Plus | UHS-I, A2, U3, V30; advertised up to 160 MB/s read and 90 MB/s write depending on model and conditions | Mobile and 4K-oriented use | Not UHS-III or LV-only-host media |
| SanDisk Extreme microSDXC | UHS-I family with A2 variants; current listings advertise up to 240 MB/s read and 140 MB/s write for specified configurations | Phones, cameras and drones | Exact SKU markings and speeds vary; cited family is UHS-I |
Advertised read/write figures are vendor “up to” claims tied to particular models and test conditions. They do not establish UHS-III or LVS compliance.
Buying checklist
- Match the form factor: SD or microSD.
- Confirm capacity and host support for SDHC, SDXC or SDUC.
- Identify the host’s bus: UHS-I, UHS-II, UHS-III or SD Express.
- For video, match the required UHS Speed Class and Video Speed Class.
- For apps, verify A1/A2 support on both host and card.
- Check whether the device requires an LV/LVS-marked card.
- Use a reader that supports the intended transfer mode.
- Consider endurance, warranty and the manufacturer’s compatibility list.
Frequently Asked Questions
Is A2 faster than UHS-III?
They cannot be ranked directly. A2 specifies application I/O behavior; UHS-III specifies a bus interface.
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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)
Does A2 matter for 4K video?
Usually not as the deciding label. Use the camera’s required sustained-write, UHS Speed Class or Video Speed Class rating.
Can an LV card work in an older SD device?
An LVS card is designed for conventional 3.3 V hosts, although it may operate in the older host’s slower or legacy mode.
Does a 624 MB/s label guarantee that speed?
No. It is the UHS-III interface ceiling; host support, flash, controller, reader and workload determine actual transfers.
Is UHS-III faster than SD Express?
The architectures differ. SD Express uses PCIe/NVMe and can provide higher theoretical rates, but only in a complete SD Express-capable chain.
The Bottom Line
Read the labels as three independent checks: UHS-III for the bus, A2 for application-oriented I/O, and LV/LVS for electrical signaling compatibility. Choose the class your device explicitly supports, then verify the video rating, reader and sustained workload instead of relying on the biggest number on the card.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
