The Fastest Memory Cards Money Can Buy

Nobody has ever complained about a memory card being too fast and, increasingly, electronics manufacturers are expecting you to have high-speed memory cards that are compatible with certain features. These days, smartphones, tablets, and even laptops often rely on memory cards to expand their storage. With consumers demanding higher resolution and less compressed video from cameras, manufacturers have responded by supplying memory cards that are not only more durable, but more capable. Today, cameras are recording 4K video to microSD cards and raw HD video to SD cards. Luckily, memory cards have kept up with the rising demand, and the fastest cards around rival SSD drives, though finding out which ones are truly fast can be a challenge.

Determining Card Speed and the Dreaded “Up To”

When memory card manufacturers list their cards’ read and write speeds, they often use terms like “up to” or “maximum” when reporting the spec. A maximum read speed or speed “up to” a certain amount is the maximum burst speed of a card. It might be able to sustain that speed for a few seconds, which is great for saving a picture quickly, such as when shooting Sony’s Alpha a9 or Alpha a9 II at their maximum burst rate of 20 frames per second, but don’t expect to see read and write speeds like that for sustained transfers, such as when you’re shooting video. Plus, some manufacturers are a bit more liberal with the speeds they quote than others. Sustained transfer speeds can vary greatly from card to card, so to determine a memory card's overall speed—just looking at the card's advertised maximum speed isn’t always the best yardstick.
It is also important not to confuse bits and bytes. Bits are abbreviated with a lowercase b (as in Mb/s), while bytes are abbreviated with a capital B (MB/s). There are eight bits in one byte. Often, video-recording codecs will list their speeds in bits per second, while cards list their speeds in bytes per second. So, when a video camera like the GH5 records at 400 Mb/s, remember that is “only” 50 MB/s.