Why does the speed class of a microSD card matter? Understanding the technology inside these tiny cards helps you make an informed choice.

Inside a microSD Card

A microSD card consists of NAND flash memory chips and a controller chip. The controller manages data distribution, error correction, and communication with the host device (your Switch).

NAND Types

• TLC (Triple-Level Cell): Stores 3 bits per cell. Affordable but slower write speeds
• QLC (Quad-Level Cell): Stores 4 bits per cell. Cheapest option, but slowest and least durable

Most consumer microSD cards use TLC NAND. QLC cards are becoming more common in high-capacity models.

Understanding Speed Classes

UHS Speed Class (U1, U3)

U1 guarantees a minimum sequential write speed of 10MB/s. U3 guarantees 30MB/s. These are minimums, not averages. A U3 card is strongly recommended for gaming.

Application Performance Class (A1, A2)

This rating measures random IOPS (input/output operations per second), which is critical for game loading. Games access many small files in a random pattern, not a single large sequential file.

• A1: 1500+ random read IOPS, 500+ random write IOPS
• A2: 4000+ random read IOPS, 2000+ random write IOPS

A2 cards are roughly twice as fast as A1 for random access.

The Switch’s Speed Limit

The Switch’s microSD card reader uses the UHS-I interface, which has a theoretical maximum of 104MB/s. Cards advertised at 170MB/s or higher will be limited to around 90–100MB/s in the Switch. This means you do not need the absolute fastest card available — a good U3/A2 card around 130–160MB/s is more than sufficient.

Why Capacity Affects Speed

Larger capacity cards often have more NAND channels working in parallel, which can increase read and write speeds. A 256GB card from the same product line is typically faster than the 64GB version. This is another reason to avoid going too small.

Summary

The science behind microSD cards explains why A2-rated, U3 cards from reputable brands deliver the best gaming experience. The Switch’s hardware limit means ultra-fast cards offer diminishing returns, so focus on consistent performance rather than peak advertised speeds.