How to Choose the best SD Card for Best Performance
Technology

How to Choose the best SD Card for Best Performance

How to Choose the best SD Card for Best Performance

Choosing an SD Card (also known as a memory card) can be a headache if one doesn’t know the types of memory cards that exist and how they work. In this post we are going to be looking at the different types of SD cards that exist and how to choose between them. But first let us look at what an SD card is.

What is an SD Card?

A Secure Digital (SD) card is a tiny portable flash memory card designed for use in various portable devices, such as car navigation systems, smartphones, digital cameras, music players and personal computers. It is a form of non-volatile memory, which means it retains the stored memory even after being disconnected from the power source.

If you have a digital camera, video camera, or smartphone, chances are you have used SD cards a lot.

SD cards come in three different sizes,

  • SD
  • miniSD
  • microSD

SD Cards

The size you need depends on your device. For example, a majority of compact cameras use SD cards, while microSDs are used in drone cameras and smartphones.

The SD Association

One of the best thing about SD Cards is their compatibility. For example, you can just remove an SD Card from your smartphone and insert it straight into your music player without facing compatibility issues, despite the phone and the music player being made by different companies. How did that came to be?

Back in 2000, three technology giants of that time —Panasonic, SanDisk, and Toshiba — got together to form the SD Association. The goal of the association was to set industry standards and encourage the development of devices that use secure digital technology. The group now has a membership of over 1 000 members.

Among other things, the SD Association is responsible for making sure that all manufacturers make SD cards that meet the same functionality and performance standards. Because of that, you can remove a Samsung SD Card from your Samsung smartphone and replace it with SanDisk SD Card without requiring a special adapter.

The SD Association also laid out the terms and differentiators that help us differentiate SD Cards based on performance and type. Such terms include the terms for SD Card Size:

  • SD
  • miniSD
  • microSD.

SD Card size

The table below shows the different sizes of SD Cards that exist and where they are used.

SD Card Size Typically used in Types of Cards
Standard SD Laptops, computers, printers, camcorders, digital audio recorders, eReaders SD, SDHC, SDXC
miniSD Digital cameras, older PDAs, computers, printers, card readers, some digital musical instruments SD, SDHC
microSD card Smartphones, tablets, personal media players (slotMusic, MP3 players, etc.) SD, SDHC, SDXC

SD card size is the easiest attribute to figure out as there are only three sizes:

  • standard (biggest)
  • mini (medium)
  • micro (smallest).

SD card size adapters

The obvious compatibility issues between the different sizes of cards is that, if the card doesn’t fit in the slot, then it won’t work. Unless you have a size adapter. The size adapters can let you insert:

  • a microSD card into a miniSD or standard SD slot
  • or a miniSD card into a standard SD card slot.

Usually, when you buy a MicroSD card, it comes with at least one adapter that you can use, for example when inserting the microSD card into an SD slot. This means that you cannot use a larger card in a slot designed for a smaller card but you can use an adapter to put a smaller card into a larger slot–for example, microSD to standard SD.

SD Card Capacity

When it comes to SD Card capacity, there are three common types of SD cards:

  • Secure Digital Standard-Capacity (SDSC, or just SD)
  • Secure Digital High Capacity (SDHC)
  • Secure Digital eXtended Capacity (SDXC.)

SDUC, Secure Digital Ultra Capacity, is the fourth type but not yet common. The memory capacities are shown in the table below:

Card Type Capacity
SD 2 GB and below *
SDHC up to 32 GB
SDXC 32 GB to 2 TB
SDUC 2TB to 128TB

*There are some 4 GB SD cards, but the official SD Association standard for SD type cards is a max capacity of 2 GB.

You don’t have to memorize the capacity ranges for each family of SD cards because every SD card for sale will have the capacity labeled in simple form. However, it is important to check if your device is compatible with the type of SD card you’re buying. For example, older SD host products may not be compatible with SDHC and SDXC cards, even when used with size adapters.

SD card speed

The standard for measuring SD card speed is in megabytes per second, notated as MB/s or MBps, with a capital B. 1 MB/s is equal to 8 megabits per second, or Mb/s and Mbps with a lowercase b. SD card speeds are categorized in one of three ways:

  • Speed class
  • Ultra High Speed (UHS) class
  • Video Speed class.

Speed class, covers minimum write speeds of 2 MB/s to 10 MB/s, with the class number corresponding to the minimum write speed of the card. In this class, a class 10 is the fastest, while a class 2 is the slowest. This speed category is written on the front of the SD card — the symbol looks like the class number inside of a C.

UHS speed class 1 has a minimum write speed of 10 MB/s for U1 to 30 MB/s minimum write speed for U3. The UHS speed is designated by a symbol that looks like a U with the class number inside it.

The video speed class, is has a V symbol ahead of the class number. In this category, the class number is equal to the minimum write speed, so a V6 writes at least 6 MB/s, a V90 at least 90MB/s.

The table below shows the different classes of SD Cards and their speeds.

Speed Class Minimum transfer speed Recommended Uses
Class 0 Legacy. No speed rating. Backing up, transferring and storing photos, music and other files
Class 2 2 MB/s File storage, SD video recording
Class 4 4 MB/s File storage, SD and HD video recording
Class 6 6 MB/s File storage, SD and HD video recording
Class 10 10 MB/s HD video recording, HD still consecutive recording
U1 10 MB/s Large size HD video recording (1080p), high-quality video capture for real-time broadcasts (i.e. HD TV shows)
U3 30 MB/s Large size HD video recording (1080p and 4k), high-quality video capture for real-time broadcasts (i.e. HD TV shows) at 60/120 FPS
V6 6 MB/s HD video from 720p to 1080p
V10 10 MB/s Full HD video and live broadcasts in 1080p
V30 30 MB/s 1080p and 4K HD videos at 60/120 fPS
V60 60 MB/s 8K HD videos at 60/120 fPS
V90 90 MB/s 8K HD videos at 60/120 fPS

The Speed Class of an SD card refers to the minimum write speed of the card, which is always a bit lower than the reading speed since reading from a card is always faster than writing to a card. There are other speed standards aside from the standard Speed Class set of SD cards. One example is the UHS Speed set which is faster than the Class set.

The difference comes from the fact that there are three different bus types used by SD cards when interfacing with hosts. These are:

  • the normal bus (default speed)
  • the high-speed bus
  • the ultra-high-speed bus.

Normal bus and high-speed bus cards fall into the Speed Class range. Cards that use the ultra-high-speed (UHS) bus fall into the UHS Speed Class.

Inspite of UHS-I SD cards having write speeds up to 104 MB/s, U1 is only guaranteed to have a minimum write speed of 10 MB/s and faster when used with a UHS device. Some UHS-I cards are backward compatible and will work with Class 2, Class 4, or Class 6 devices, but you obviously won’t get the same speed as you would with a UHS-I device.

Besides UHS, there is Video Speed Class, introduced in 2016 by the SD Association. This new speed class spans both the high-speed bus and the UHS bus and include the speed ratings V6, V10, V30, V60, and V90. It is intended for HD video recording from 720p all the way up to 8K.

In terms of speed, the V6 is the same speed as a Class 6 and a V10 is the same speed as a Class 10, but the V cards support modern MLC NAND Flash technology and other requirements ideal for video recording.


Which Card to Buy?

Though it might be tempting to shop for the biggest card you can find, you should check if your device is compatible with the SD card you are trying to buy. SDHC and SDXC cards are backward compatible, but SD hosts are not forward compatible.

Most devices can use SD, SDHC, or SDXC interchangeably, but if you have something like an older digital camera, that may not always be the case. It might not support SDXC. Here is some tips on device support:

  • Devices released after 2008 are typically compatible with SDHC
  • most devices launched after 2010 will work with SDXC.
  • The original SD card is compatible with any SD device.

SDSC, or just SD, can hold up to 2 GB. SDHC can hold up to 32 GB. SDXC can hold up to 2 TB. 2 TB might be tempting, but be careful, some older devices may not be able to read/write to SDHC or SDXC cards. So check your device manual. You don’t want to end up buying a 64GB card for a smartphone that supports up to 32GB.

Speed matters too. If you are tempted to buy the fastest card that exist, remember speed corresponds to price. Instead you should check with your device’s manual for the recommended card speed. It’s never wise to choose a slower card than recommended because it will sacrifice the performance of your device. However, on the other end, an SD card faster than the recommended speed may still not give you a performance boost if your device may not support faster card speeds.

In general, for HD video recording, you’ll need at least a Class 4 card, whilst Class 2 cards and slower are fine for SD video recording and backing up or transferring files.

So, before buying a card check if its Speed Class rating and type is compatible with your device? Here is how the cards will be inscribed:

  • 16 GB SDHC Class 4 60x Speed Flash Memory Card – The 16 GB is the capacity, that is 16 Gigabytes. The card is an SDHC card. Remember, SDHC cards are between 2 GB and 32 GB. Ignore the 60x for now. That is the x-speed class rating and it does not come under regulation by the SD Association. Class 4 card means it has a minimum write speed of 4 MB/s.
  • 64 GB SanDisk Ultra SDXC Class 4 15 MB/s*- This one shows the Speed Class Rating along with the MB/s value. However, the Ultra and 15 MB/s* on the label are not official SD Association ratings but manufacturer standards. For example, in this case, the asterisk is meant to indicate that 15 MB/s is the maximum transfer speed. SDXC is the type of the card. However be careful with this one as SDXC cards are not usually compatible with older devices.

Mathematics, Chemistry and Physics teacher at Sytech Learning Academy. From Junior Secondary School to Tertiary Level Engineering Mathematics and Engineering Science.

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