Types and differences of SD memory cards

SD cards (Secure Digital) are today the most common form of removable storage media for all portable devices: tablets, cameras, camcorders, cell phones, smartphones and laptops.

Various types of memories are available, of different sizes, capacities and speeds; in these cases it is quite easy to make a mistake. To avoid unpleasant situations, to avoid wasting money on cards with low memory capacity, low speed or unreadable and to buy the right memory SD card for your purpose, it is important to understand the differences between SD card modelswhich are not at all the same even with the same size.

Although we cannot indicate here exactly what to buy for each type of device, let’s look at them general information to be prepared when you go to buy a new SD card.

READ ALSO -> Choosing the best MicroSD for Android smartphones

1) microSD features

For microSD we can take four parameters into consideration to choose the best card for our technological device (smartphone, tablet or portable camera):

  • Speed ​​class
  • Bus speed
  • Application speed
  • Capacity
  • Card size

To understand which parameter is best to focus on, we will show you what the various parameters mean and what the differences are between apparently similar but profoundly different products.


For SD Cards there are different classes that can be purchased: class 4, class 6 or class 10. This number simply allows you to know the minimum card writing speed. The card number indicates the MB per second that the card can write to itself at least.

For example, a class 2 SD card writes at 2 MB/s. Besides these classes are also available UHS classes (class U1 and class U3) and video classes (from V6 to V90) which identify the fastest SD cards, dedicated to filming and shooting professionals for making videos and saving very high definition photos in fractions of a second. One class does not necessarily exclude the other: a class 10 is also U1 and V10while the fastest ones now available on the market are the U3/V30, the V60 and the V90.

Bus speed

In addition to the writing speed of the individual card, we will also have to examine the speed with which data leaves and enters the card; this is why we talk about bus speed (i.e. the speed of the metal contacts in exchanging data).

This speed can be classified on SD cards by a Roman symbol saved in one corner of the card; currently the normal classes (without Roman symbols), class I (first Roman numeral), II (second Roman numeral) and class III (third Roman numeral) are available.

To get the best results in terms of transfer speed we will have to only adopt SD cards that have Roman numerals (I, II and III)so as to be sure of making the most of the writing and reading speed.

An even more recent technology is the SD Expresswhich allows you to reach very high speeds (up to 3938 MB/s), thanks to sharing the bus with PCI Express 4.0 ×2. Obviously the device into which we are going to insert the SD card must also have the same compatibility, otherwise it will not be used adequately.

Application speed

Another parameter examined is the application execution speed, measured with le sigle A1 e A2. The abbreviation A1 identifies a reading speed of 1500 IOPS and write 500 IOPS; the acronym A2 instead identifies the fastest microSD for running apps and games (for example on Nintendo Switch), given that it has a writing speed of 4000 IOPS and a reading speed of 2000 IOPS.

SD memory capacity

The capacity of the SD card is the most obvious value in a shop window or at the mall. To avoid spending money unnecessarily on an SD card that is too small or too large, we need to determine more or less what we need for our electronic device. Take into account that currently there are three main types of SD cards with different capacities. The types of MicroSD cards found on the market are the following:

  • SDSC o Secure Digital Standard Capacitywith a memory capacity of 128 MB to 2 GB and FAT file system which is not compatible with the latest smartphones;
  • SDHC o Secure Digital High Capacity they have a memory capacity ranging from 4 GB to 32 GB, uses the FAT file system and is compatible with practically any modern device;
  • SDXC o Secure Digital Extended Capacity they have a memory capacity of 64 GB to 2 TB and use the exFAT file system; compatible with a large number of modern devices.
  • SDUC: Minimum capacity of 2 TB and maximum capacity of 128 TB, with exFAT recommended file system.

Considering that digital cameras on the market today start from 13 megapixels and higher and smartphone cameras start from 10 megapixels, we make the choice of card based also on the number of photos we can save on it: a 2GB SD card can hold approximately 380 photos saved in JPEG format, but not even 100 if taken in RAW format.

After inserting the memory card into the camera, take a photo and then check the data on the screen to see how many images the card can hold based on the shooting mode (JPEG, RAW, TIFF)
In this table, an estimate of how many Jpeg images can hold Memory cards of various sizes, taking photos with different cameras.

In the case of smartphones we will also have to take into account the use of the SD memory card as a space where music files, video files and data files of some apps can also be saved (such as maps of navigation apps) so it is better to be provident and focus on models from 128 GB and up.

Card size

Talking about SD cards in terms of size there are actually tre different models:
– Format Standard (32mm x 24mm)
– Format MiniSD (31,5 millimeters x 20mm)
– Format MicroSD (11mm x 15mm)

Each device should indicate what type of card it wants in the specifications, so you never make mistakes. Smartphones always use microSD while cameras generally use the Standard format or at most the miniSD format (although SD adapters are increasingly popular to accommodate smaller formats without problems even in the larger slots).

2) Buying guide

Taking into account that the most reliable manufacturers of memory cards are Samsung, Sandisk, Fuji, Lexa, Delkin, Viking and Kingston, let’s see together which cards we can buy in the two most used formats, namely microSD and SD Card.

Let’s start by showing you the microSD to purchaseusable both on compatible phones and within portable devices (such as game consoles or multimedia players):

  • Samsung Evo plus 128GB: microSD SDXC U3, class 10 A2, 130MB/s high-speed memory card.
  • SanDisk 128 GB Ultra: microSDXC UHS-I card with SD adapter, speed up to 140MB/s, A1 app performance, Class 10 speed, U1 speed.
  • SanDisk 128 GB Nintendo Switch: specific card for Nintendo Switch, Nintendo Licensed memory card, speed up to 100 MB/s, UHS-I Class 10, U3 speed.
  • Amazon Basics MicroSDXC: 128GB memory card with SD adapter, A2 speed, U3 speed and read speed up to 100MB/s.
  • SanDisk 128 GB Extreme PRO: microSDXC card with SD adapter and RescuePRO Deluxe system, speeds up to 200 MB/s, A2 app performance, UHS-I class, Class 10 U3 and V30 video speed.

Let’s see instead which SD Cards can we buyto be used mainly on GoPros, drones or filming devices (such as reflex cameras):

  • SanDisk 128GB Extreme PRO: scheda SDXC, fino a 300 MB/s, UHS-II Class 10 U3 V90.
  • Lexar SDXC: Professional 64GB SD Card, 2000x UHS-II card speed, class V90, class U3.
  • SanDisk 256GB Extreme PRO: SDXC memory card up to 170MB/s, class UHS-1, class 10, speed class U3 and video speed V30.
  • Kingston Canvas React Plus 256GB: 256GB UHS-II professional memory card, U3 class, V90 video speed (FullHD/4K/8), 300MB/s read speed and 260MB/s read speed.

We choose the right format based on the device and the speed we need.


For digital cameras and SLRs it is advisable to focus above all on memory space, therefore on 128 GB models.

For digital video cameras we consider class U1 and class I cards for videos with resolutions up to Full HD (1920 x 1080).

For 4K or high frame rate videos we recommend focusing only on SD cards (of any type) with class U3, class II and class V60 or V90, so as to have the right writing speed when recording videos at these resolutions. For smartphones usually very high speed is not required, but let’s make sure that the minimum is always an SD card with class 10, U1 and class I to be comfortable in any scenario.

On the subject we can also read the following guides on how Optimize memory cards and SD memory cards for cameras and cell phones and on Programs for recovering deleted files and photos from memory cards and USB sticks.

Leave a Reply

Your email address will not be published. Required fields are marked *