Storage and memory cards question

SDHC, SDXC, UHS-I, U3 and V30: which label answers which question?

Separate card shape, capacity family, bus interface and recording class instead of comparing unlike labels.

The answer

Short answer SDHC and SDXC are capacity, UHS-I is the bus interface, and U3 and V30 are performance classes.

SDHC and SDXC describe capacity families. UHS-I names a bus interface. U3 and V30 are performance-class symbols, not connector forms or measured peak transfer speeds.

Full-size SD card formComputer-generated illustration, not a photograph

microSD card form — original, not-to-scale identification schematic; drawing review pending — microSD card formOriginal identification schematic · not to scale · review pending

Why the simple answer is not enough

Keep the evidence layers separate

1Reasoning step

Record four separate fields: form factor, capacity family, bus interface and the class required by the host. One label cannot fill the other three.

2Reasoning step

Capacity boundaries describe the standard, not the maximum accepted by a particular device. A physically fitting card can still be outside the host’s documented capacity support.

3Reasoning step

Use the required class-symbol family in the host manual. An equal number or equal minimum write-speed value in a different family is not sufficient evidence of the requested class match.

4Reasoning step

Bus ceiling, class minimum and measured application throughput answer different questions. No benchmark or automatic recording-mode recommendation is produced here.

Capacity classes — standard boundaries, not an exact-device approval
Family	Capacity range	Standard file system	Evidence
SD	Up to 2 GB	FAT12 / FAT16	C068B (private workspace)
SDHC	Above 2 GB to 32 GB	FAT32	C068B (private workspace)
SDXC	Above 32 GB to 2 TB	exFAT	C068B (private workspace)
SDUC	Above 2 TB to 128 TB	exFAT	C068B (private workspace)

Scroll horizontally on narrow screens. These are standard family definitions, not claims of products available today or instructions to change a file system.

What to check next

Read the exact host model and its supported form/capacity family.
Record the bus name separately from the class symbol.
Match the class family requested in the manual; use same or higher class within that family as documented.
Keep existing data backed up; this reference neither formats a card nor proves that reformatting will make it supported.

Canonical connector and cable notes

Full-size SD card formSD and microSD are distinct physical card forms. The form-factor label does not by itself establish capacity class, bus mode or recording performance.microSD card formThe SD Association treats microSD as a separate, smaller form factor from full-size SD. Capacity, bus interface and speed-class support remain additional distinctions.SD capacity classes: SD, SDHC, SDXC and SDUCThe SD Association defines SD up to 2 GB, SDHC above 2 GB through 32 GB, SDXC above 32 GB through 2 TB, and SDUC above 2 TB through 128 TB. These are capacity families, not speed ratings.UHS-I and UHS-II bus interfacesThe SD Association lists UHS-I SDR104 at 104 MB/s and UHS-II at 156 MB/s full duplex or 312 MB/s half duplex. These bus figures are not guaranteed sustained card-write rates.

Related permanent comparisons

SD capacity versus bus interfaceCapacity family and transport technology are different layers.SD versus microSDCompare physical card forms; verify capacity, bus and speed class separately.

Your next step

Continue with the relevant reference.

Capacity-family reference Bus-interface reference Exact-device port explorer

Question pages do not create compatibility verdicts.

They reorganize facts and uncertainty already represented in the atlas. Exact-device, cable, protocol, power, safety and performance requirements remain separate where the evidence says they are separate.

Evidence behind this page

Scope first. Source second. Approval separate.

7 linked sources · 12 scoped claims · 0 sources with inspection/access flags.

Page scope: Evidence attached to records and cable profiles referenced by this guide; not a sentence-by-sentence editorial approval.

Assessment 2026-10-22 · earliest scheduled source review 2026-12-30. This is a recorded-date assessment, not a live source check. Page-level independent review is not established by this panel.

Inspect 7 source scopes, access limits and dates

S041 · SD Standard Overview

SD Association · Standards-organization domain · inspected 2026-10-07 · due 2027-01-05

Within inspection window

Scoped support: SD/microSD physical-form and generation-specific contact-count distinctions; no numbered assignments or fabrication drawing.

Not established / limitations: Counts are scoped to named modes. The overview does not identify an exact card or host, and extra-row count does not establish implemented protocol.

Locator: Conventional-card paragraph and form-factor table: first-row counts and UHS-II / SD Express count ranges

S042 · Capacity: SD, SDHC, SDXC and SDUC

SD Association · Standards-organization domain · inspected 2026-10-07 · due 2027-01-05

Within inspection window

Scoped support: SD capacity/file-system classes and nominal full-size SD and microSD envelopes; not host capacity approval.

Not established / limitations: Nominal card envelopes are identification aids, not mechanical tolerances, socket footprints, pad positions or formatting instructions.

Locator: Capacity ranges, file-system table and Form Factor Size rows

S043 · Bus Speed: Default, High Speed, UHS and SD Express

SD Association · Standards-organization domain · inspected 2026-10-01 · due 2026-12-30

Within inspection window

Scoped support: Specified bus modes and distinction from measured card performance.

Not established / limitations: Specified bus modes and distinction from measured card performance.

Locator: Bus interface table; duplex explanation; final speed caveat

S044 · SD Speed Class

SD Association · Standards-organization domain · inspected 2026-10-07 · due 2027-01-05

Within inspection window

Scoped support: Minimum sequential-performance class symbols and same-family host/card matching under defined conditions.

Not established / limitations: Bus modes and performance classes are distinct. Shared numeric minima across different class symbols do not guarantee the requested host class; no particular video mode is approved.

Locator: Speed-class families and Best Combination between Speed Class Host and Card

S045 · SD Express implementation overview

SD Association · Standards-organization domain · inspected 2026-10-01 · due 2026-12-30

Within inspection window

Scoped support: PCIe/NVMe transport and explicit host capability verification.

Not established / limitations: PCIe/NVMe transport and explicit host capability verification.

Locator: Host implementation overview and PCIe-only host distinction

S391 · S-46u Industrial MICRO SD/SDHC Memory Card — Revision 1.00

Swissbit AG (manufacturer document hosted by Farnell) · Unclassified publisher domain · inspected 2026-10-07 · due 2027-01-05

Within inspection window

Scoped support: Exact Swissbit S-46u conventional microSD pin-label example; native SD-mode assignment and orientation.

Not established / limitations: Distributor-hosted manufacturer PDF, not an independently authenticated original. No universal SPI, SD Express or UHS-II pinout; original 19-page document is linked, not redistributed.

Locator: Page 8, Figure 2 bottom view and Table 11 native SD / SPI pad assignments

S392 · SD Express (SD7.x–SD8.0) Host Implementation Guideline, Version 2 — May 2025

SD Association · Standards-organization domain · inspected 2026-10-07 · due 2027-01-05

Within inspection window

Scoped support: Named-version SD Express connector/host context, particularly the different microSD Express and microSD UHS-II second-row geometry.

Not established / limitations: Targeted sections only, not a full licensed specification review. No claim that every legacy, Express or multi-mode host supports another card; no fabrication approval.

Locator: Page 13, sections 4.10.1 and 4.10.2; context in pages 7–8

Trace 12 claims to their source records

C061A · P061

SD and microSD are distinct physical card forms. The form-factor label does not by itself establish capacity class, bus mode or recording performance.

Claim scope: Named standard or manufacturer description only; procedural checks are editorial recommendations, not hardware tests.

Source links: S041 · Evidence trail → (private workspace)

C061B · P061

The SD Association lists a nominal full-size SD card envelope of 32 × 24 × 2.1 mm. Conventional single-row cards for Default Speed, High Speed and UHS-I use nine contacts.

Claim scope: Nominal card identification and conventional first-row contact count only; not a socket footprint, pad drawing, tolerance specification or all-generation pin count.

Source links: S041 · S042 · Evidence trail → (private workspace)

C061C · P061

The SD Association overview distinguishes full-size SD contact counts by interface: High Speed/UHS-I nine, UHS-II seventeen, one-lane SD Express seventeen to nineteen, and two-lane SD Express twenty-five to twenty-seven.

Claim scope: Published overview categories inspected 2026-10-07; count ranges retain implementation variation and do not assign individual pins or identify a host controller.

Source links: S041 · Evidence trail → (private workspace)

C062A · P062

The SD Association treats microSD as a separate, smaller form factor from full-size SD. Capacity, bus interface and speed-class support remain additional distinctions.

Claim scope: Named standard or manufacturer description only; procedural checks are editorial recommendations, not hardware tests.

Source links: S041 · S045 · Evidence trail → (private workspace)

C062B · P062

The SD Association lists a nominal microSD envelope of 15 × 11 × 1.0 mm (length × width × thickness). Conventional single-row cards for Default Speed, High Speed and UHS-I use eight contacts.

Claim scope: Nominal microSD card identification and conventional first-row count; no inference about extra contacts, exact host support or fabrication dimensions.

Source links: S041 · S042 · Evidence trail → (private workspace)

C062C · P062

The SD Association overview distinguishes microSD contact counts by interface: High Speed/UHS-I eight, UHS-II sixteen, and one-lane microSD Express sixteen to seventeen.

Claim scope: Published overview categories inspected 2026-10-07, not an exhaustive identification method; physical contacts do not establish active bus support.

Source links: S041 · Evidence trail → (private workspace)

C062D · P062

Swissbit S-46u Revision 1.00, page 8, gives this native SD-mode assignment in Figure 2 bottom-view numbering: 1 DAT2, 2 CD/DAT3, 3 CMD, 4 VDD, 5 CLK, 6 VSS, 7 DAT0, 8 DAT1. The same table gives different SPI-mode functions on several pads.

Claim scope: Exact manufacturer-documented conventional microSD example; native SD-mode column only. Not a UHS-II/Express extra-row pinout, socket-terminal map, startup sequence or universal SPI wiring guide.

Source links: S391 · Evidence trail → (private workspace)

C062E · P062

The SD Association SD Express Host Implementation Guideline Version 2 (May 2025), section 4.10.2, states that microSD Express needs different connectors because the second-row pad location and size differ from microSD UHS-II.

Claim scope: microSD second-row mechanical distinction in the named guideline; not proof of compatibility or incompatibility of any complete multi-mode host product.

Source links: S392 · Evidence trail → (private workspace)

C068A · P068

The SD Association defines SD up to 2 GB, SDHC above 2 GB through 32 GB, SDXC above 32 GB through 2 TB, and SDUC above 2 TB through 128 TB. These are capacity families, not speed ratings.

Claim scope: Named standard or manufacturer description only; procedural checks are editorial recommendations, not hardware tests.

Source links: S042 · Evidence trail → (private workspace)

C068B · P068

The SDA capacity classes are SD up to 2 GB, SDHC above 2 GB through 32 GB, SDXC above 32 GB through 2 TB, and SDUC above 2 TB through 128 TB. The standard file-system associations are FAT12/16, FAT32, exFAT and exFAT respectively.

Claim scope: Standard class boundaries, not a device maximum, card availability claim or instruction to format existing data.

Source links: S042 · Evidence trail → (private workspace)

C069A · P069

The SD Association lists UHS-I SDR104 at 104 MB/s and UHS-II at 156 MB/s full duplex or 312 MB/s half duplex. These bus figures are not guaranteed sustained card-write rates.

Claim scope: Named standard or manufacturer description only; procedural checks are editorial recommendations, not hardware tests.

Source links: S043 · Evidence trail → (private workspace)

C069B · P069

UHS-I and UHS-II name bus interfaces; U1/U3 and V6/V10/V30/V60/V90 belong to speed-class symbol families. The SDA warns that matching numerical write-speed minima across different symbol families does not establish the host/card class match.

Claim scope: Label interpretation and defined minimum sequential-performance conditions only; not a measured transfer rate, blanket recording-mode recommendation or certification of an individual card.

Source links: S043 · S044 · Evidence trail → (private workspace)

Prepare this page for review →Read the evidence method →

Recorded evidence only. An inspection date, publisher label, source link or generated packet is not independent technical review, hardware testing, fabrication approval or a compatibility verdict.