Forward-looking: It's unclear when, but users could soon see SD cards with significantly faster transfer speeds due to new hardware specifications. A labeling system will also help manufacturers and consumers determine the right cards for various devices based on minimum performance.
The SD Association recently released the SD Express 9.1 specification, which defines newly upgraded standards for vendors manufacturing SD cards and supporting hardware. The new requirements include PCIe 4.0 and NVMe architectures, which could double maximum speeds to 2GB/s.
Additionally, the 9.1 specification introduces a new labeling system to indicate which speed class each device requires and what each SD Express card supports. The four tiers (pictured below) represent minimum read/write speeds ranging from 150MB/s (like SanDisk's recently announced 1.5TB card) to 600MB/s. Customers must check a product's packaging or instruction manual to ensure they use the right card for each device.
Speed isn't the only innovation the specification brings. The association also introduced multiple simultaneous data streams and methods to manage power and thermals.
Multi-stream support enables users to record and transfer multiple feeds onto an SD card if their total data rate doesn't exceed the card's speed class. The association predicts that video feeds from vehicles or surveillance systems will benefit the most from the new feature.
Also read: microSD and SD Card Buying Guide - Classes, Performance, What to Buy
Meanwhile, the new power and thermal management systems ensure cards avoid damage from excessive heat. Asus ROG Ally owners recently encountered this problem when the handheld gaming PC's SD card reader either throttled speeds or stopped working altogether due to overheating.
The first new countermeasure for the issue allows a card to tell a host device its preferred maximum power level based on its speed class and PCIe bus mode so the hardware doesn't devote too much energy to reading and transferring data. Secondly, SD cards under the 9.1 specification can deliver information on their unique thermal limits, which may vary due to differences in performance, structure, and materials. The data could help future devices provide optimal speeds while monitoring heat levels.
As the specs require new hardware, it will likely take time for SD cards and readers supporting the new speeds to reach the market. Afterward, the association plans to release specifications allowing transfer speeds up to 4GB/s.