Secure Digital cards, commonly known as SD cards, were first developed in 1999 by SanDisk, Toshiba, and Panasonic companies. Since the launch of SD cards, they have undergone various iterations to enhance their ability to store huge amounts of data easily and conveniently. These cards are cheap, portable, and versatile, making them highly popular compared to their predecessors such as floppy disks.
Initial SD cards were similar to MultiMediaCard (MMC) in existence then, but they have evolved to miniSD and microSD cards. Though they might look alike, SD cards are not created equal as they differ in capacity, size, and speed.
Due to their versatility, memory cards have become pacesetters in the expandable storage sector. But despite their popularity, SD cards have several downsides as they are quite delicate and break or warp easily if not handled gently. Their cells also malfunction leading to loss of data.
Currently, the market is awash with SD cards bearing different features and specifications as manufacturers try to outdo each other. Confronted with so many types of cards with varying features, it is easy to get confused. One of the major concerns facing card buyers is understanding the different speed ratings embedded on cards.
Speed Class: Why is it important?
SD card speed is especially critical for video cameras as the devices are constantly recording a steady stream of content. Recording high-resolution videos on SD cards require data to be written at a specific minimum speed to preempt the possibility of frame drop which results in lost data and uneven playback. In addition, if you use a card that does not meet the minimum speed ratings on a highly advanced camera, the recording device is likely to return an error message warning that the data will be captured at a lower definition.
The same class can also be said for gaming devices such as handheld consoles. In his latest guide on the Best SD Card for Steam Deck, Glenn found out that the faster the Speed Class is, the better do the game’s load, with less lagging and faster loading times.
According to the SD Association (SDA), there are various Speed Class standards to help consumers determine what they need using symbols imprinted on the cards. The speed rating refers to the minimum write speeds of a card but they are often faster than the minimum indicated.
Standard or regular Speed Classes are denoted by a capital “C” in the logo with a digit inside the letter while cards in the UHS classes have a capital “U” with a number inside the letter.
If your card does not feature a symbol or logo, there is a possibility it is “Class 0”. This applies to older cards produced before the advent of the speed rating system and are slower than regular Class 2 cards.
SD card speed often refers to the rate of data transfer; however, there are several types of speed you should keep in mind. One of the factors to consider is the direction of data transfer. Speed for transferring the data off the SD card is known as reading speed while speed for transferring content from a device to the card is referred to as write speed. The read and write speeds of a card are different but normally, an SD card has a higher read compared to its write speed.
Though cards have higher read speeds compared to write speeds, the most important of these two is their writing speed as it determines whether the card is compatible with certain devices or not.
Megabytes versus Megabits
SD card write speed or read speed is defined using Megabytes (MBps or MB/s) or Megabits (Mbps (or Mb/s). MBps (MB/s) with an uppercase “B” means megabytes per second while Mbps (Mb/s) with a lowercase “b” means megabits per second. MB/s is used to rate the speed of file transfer or the size of the file. Mbps or Mb/s measures upload and download speeds.
Regular/Standard Speed Classes
There are several speeds under this category. These include Class 2, Class 4, Class 6, and Class 10 (C2,4,6,10). C2 is the slowest card speed in existence. Cards in this category have a minimum write speed of 2MB/s. These are ideal for activities that do not demand high write speeds and can be used for recording videos using a low-end video camera.
C4 cards support write speeds of 4MB/s. They are often used in digital cameras, smartphones, and tablets. These cards are ideal for capturing high-definition data.
Class 6 supports write speeds of 6MB/s. This is the lowest speed for anyone intending to capture 4K content. On the other hand, C10 has a minimum write speed of 10MB/s and is ideal for capturing and storing Full-HD content. Due to technological advancement, Class 2-6 cards are rarely used as modern devices require C10 cards as the minimum speed. Currently, C10 cards are the most popular in this category.
Ultra High-Speed Class
The Ultra-High-Speed Class, commonly known as UHS Class was launched by the SDA in 2009 for SDXC and SDHC cards. The category has two types: UHS 1 and UHS 3. These cards cost more compared to the regular classes and support minimum speeds of 10-30MB/s. Cards under this category were developed for content that requires high speeds, and are ideal for recording 4K content and gaming.
Ultra-High-Speed Bus Class
Ultra-High-Speed Bus Class, also known as UHS Bus Class, is a different category from UHS. It is not a rating system but rather a type of interface technology between the card and the device. Cards in this group are normally represented by a Roman numeral. Currently, there are two types in this category: UHS-I and UHS-II SD. A UHS-I card is capable of attaining maximum speeds of 104Mb/s while UHS-II supports 312Mb/s.
In 2017, the SDA announced the coming of UHS-III memory cards supporting 624MB/s but they never appeared in the market. In June 2018, faster SD Express cards which use PCIe standards for bus transfer speeds maximizing at 985MB/s were launched which seems to have dampened the UHS-III hype.
At this juncture, it is important to note that while UHS-II should allow for higher speeds than UHS-I SD card, there is no guarantee it would be faster as there are other factors to consider including the host device. To take advantage of the potential speeds of a UHS-I, II, or PCIe, the host device needs to support the card. If you insert a UHS-II SD card in a device with UHS-I capabilities, it will function, however, the card will fall back to the device’s UHS-I speeds.
Video Speed Class
This category is often identified as V + write speed for video class. The class was primarily designed to handle high-definition videos and write/read speeds. This category supports multi-file recording and can capture additional data such as height from the ground, and geographical location. The V class is a recent addition and features a minimum write speed of 6MB/s to 90 MB/s and above. A card in this category rated V30 has a 30MB/s write speed while a V90 has a write speed of 90MB/s.
Initially, the SD Association used classes to represent minimum write speeds by identifying cards such as “Class 2“, or “Class 6“. Later the association decided the class labeling contained too many letters on the SD card and changed to the class standard. U1 corresponds to a minimum speed of 10MB/s and U3 is 30MB/s.
Much later the “U“ standard was changed to “V“. Currently; you are likely to see V6, V10, V30, V60, and V90 cards. Since all these symbols are printed on cards alongside the rest of the information, things can get quite confusing. If you ever feel confused about the information on the card when looking out for a video card, just look out for the V symbol. That is the most important speed feature you will need to consider as it indicates the minimum write speed.