What is an SDXC Card?
An SDXC card stands for Secure Digital eXtended Capacity card. It is a portable flash memory card format designed to store large amounts of data, ranging from 64 gigabytes to 2 terabytes. It provides the high speed and expansive storage needed for modern high-resolution digital devices.
The SD Association introduced the SDXC format to overcome the storage limitations of older card types. As camera sensors and video resolutions advanced, older storage media could no longer handle the massive file sizes. SDXC cards use the exFAT file system, allowing them to handle individual files larger than 4 gigabytes, which is vital for continuous high-definition and 4K video recording. These cards are widely used in digital cameras, drones, gaming consoles, and laptops.
Key Takeaways
Massive Capacity: Storage space ranges from 64 gigabytes up to 2 terabytes.
Modern File System: Uses exFAT to support individual files larger than 4 gigabytes.
High Performance: Built to handle high-bit-rate data streams like 4K and 8K video.
Backward Compatibility: Works with hardware designed for newer formats, but older devices built for standard SD cards cannot read them.
History and Evolution
The Secure Digital card format has evolved through distinct generations to match rising data demands.
Standard SD: The original format topped out at 2 gigabytes of storage using the FAT16 file system.
SDHC (High Capacity): Raised the storage ceiling to 32 gigabytes using the FAT32 file system.
SDXC (eXtended Capacity): Launched in 2009, this generation pushed limits up to 2 terabytes and introduced the exFAT file system.
SDUC (Ultra Capacity): The latest specification designed to scale future storage from 2 terabytes up to 128 terabytes.
How Do SDXC Cards Work?
SDXC cards rely on non-volatile flash memory to retain data without needing a continuous power source. Inside the card, an integrated controller manages how data is read from and written to the memory cells.
The exFAT file system serves as the foundational architecture. Unlike older file systems that crash or stop recording when a single video file hits 4 gigabytes, exFAT allows files to scale up to the maximum capacity of the card. Data flows between the host device and the card through physical pins using specialized bus interfaces, which dictate the maximum theoretical speed of the transfer.
Performance Classes and Specifications
When examining an SDXC card, several speed symbols indicate its performance capabilities.
Speed Class
The original rating system, indicated by a number inside a circle (Class 2, 4, 6, or 10). Class 10 signifies a minimum sustained write speed of 10 megabytes per second.
UHS Speed Class
Designed for Ultra High Speed buses, represented by a number inside the letter U. U1 supports a minimum of 10 megabytes per second, while U3 guarantees at least 30 megabytes per second, which is the baseline for smooth 4K video capture.
Video Speed Class
The modern standard for high-resolution video recording, marked by the letter V followed by a number. Ratings range from V6 up to V90. A V60 or V90 rating ensures the card can handle the intensive data streams required for professional 8K video cinema capture.
Bus Interfaces
The physical connection speed potential of the card circuitry:
UHS-I: Achieves theoretical architecture speeds up to 104 megabytes per second.
UHS-II: Adds a second row of physical pins to boost theoretical speeds up to 312 megabytes per second.
SDXC vs. Alternatives
| Feature | SDHC Cards | SDXC Cards | SDUC Cards |
|---|---|---|---|
| Storage Capacity | 4 gigabytes to 32 gigabytes | 64 gigabytes to 2 terabytes | 2 terabytes to 128 terabytes |
| Default File System | FAT32 | exFAT | exFAT |
| Max Single File Size | 4 gigabytes | No practical limit | No practical limit |
| Device Compatibility | Works in SDHC, SDXC, and SDUC devices | Works only in SDXC and SDUC devices | Works only in SDUC devices |
Limitations of SDXC
Hardware Compatibility: Older hardware built before the SDXC standard cannot read or write to these cards, even if the card fits physically into the slot.
File System Requirements: Some older operating systems or specialized open-source devices require extra software to recognize the exFAT file system.
Physical Vulnerability: The small plastic casing can crack under pressure, and the exposed metal pins are susceptible to static discharge or scratches.
Related Technology Terms
Flash Memory: The underlying solid-state storage technology that retains data without power.
exFAT: The extended file allocation table file system optimized for flash drives.
Bus Speed: The maximum rate at which data can travel across the interface between the host device and the card controller.
Form Factor: The physical size and shape of the card, such as full-size SD or microSD.