Memory Cards Naming, Speeds and Symbols Explained

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memory cards symbols
Memory cards in this day and age come decorated with a bunch of symbols and numbers that might be confusing for the average consumer, so this article will help you understand, once and for all, what those symbols on your SD card and microSD card mean.

SD and microSD Card Symbols Explained

We will now look at the factors that SD card symbols and microSD card symbols are meant to describe.

Storage Capacity

Even though the most commonly used memory cards are either SD or microSD cards, there are a few other types as well. This is the first symbol we’re looking at; it describes the storage capacity of your memory card by naming the file system that it uses. You may see any of the following symbols on your card, followed by its storage capacity in GB.

  • SD, which means Secure Digital, and these are the oldest kind of card and also the least used. MicroSD cards are smaller in size but use the same technology. Most SD cards are limited to 2 GB of storage.
  • SDHC, or Secure Digital High Capacity cards use newer technology and have up to 32 GB of storage available.
  • SDXC, or Secure Digital Extended Capacity cards are the latest ones; they boast storage of up to 2 TB, but some older systems and card readers may not be compatible with this kind of memory card since it is a bit larger as well.

That being said, more storage isn’t always a good thing – it is advisable to use multiple cards if you need more storage because, after all, cards do get lost or get corrupted.

Bus Class

The UHS Bus Class is a rating that describes a card’s bus interface, and it is usually represented on the card using a roman numeral. There are three categories for this: UHS-I, UHS-II, and UHS-III, but only the numeral itself appears on the actual card. UHS stands for Ultra High Speed.

Speed Ratings

Almost all other symbols on a memory card are some form of speed rating, so now we will look at microSD and SD card speed from that viewpoint.

The Actual Card Speed

This is the really confusing part because memory card speed can be expressed either as MB/s or in the form of ‘x’ ratings – and sometimes both at the same time. The MB/s speed is straightforward and simple to understand, but some brands only quote the ‘x’ speed, which is a speed factor.

All this does is require mental math from the user whenever it comes to compared card speeds. 1x equals a speed of 150 kb/s, so, for instance, 600x would mean speed of 90 MB/s. The speed expressed in terms of this rating is also called the “read” speed and is typically higher than the “write” speed.

Speed Classes

Next, we have speed classes, which can be a couple of different types. The basic speed class is written on the card as a number inside the letter C. This number represents the minimum write speed, and it is mostly important in terms of video and image processing. There can be four classes here: 2, 4, 6, and 10. The higher the class, the faster the card.

There is also UHS Speed Class, which is different from UHS Buss Class. This is the speed rating used for newer cards like SDXC ones. For this rating, the class is written as a number inside the letter U. Lastly, there’s Video Speed Class, which should concern you if you care about shooting high-quality videos – 4k or even 8k. This is a separate class of cards whose ratings range from 6 to 90; the higher the rating the higher your write speeds will be.

Side Note on Speed Ratings

There are some additional things to consider about memory card speed before you rush out to buy one. In most cases, the read speed will always be faster than the write speed, which means the speed written on the card is always the read speed. Manufacturers will want to put the bigger number on the card, so this read speed is also likely a peak maximum read speed and not a sustainable one, which tends to be slightly lower.

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