Welcome to the ultimate memory card guide! You likely thought that all the memory cards were the same when buying an SD card or micro SD, but you will almost certainly have seen that there are many types of cards with lots of different features.
Depending on the device you need the SD card, you must choose the appropriate UHS BUS class, speed class, app performance class, etc…
V30? SDXC or SDHC? How much capacity do I need it? These are questions that a lot of people ask the other every day. To solve all those doubts, I have prepared this guide to purchase SD and micro SD memory cards.
And if you get to the end of the article, I’ll leave you the best deals on updated SD and micro SD cards!
What is an SD card?
An SD card (short for Secure Digital)is a memory card designed to store data and content on portable devices, such as mobile phones, digital photography and video cameras, tablets, game consoles or GPS browsers.
Today, SD cards are undoubtedly one of the most popular storage media, thanks in part to the large capacity they offer in such a small size.
Before you buy an SD card, you should take into account, broadly speaking, three factors:
- Type or size
- Read/write speed
SD card types
There are mainly 3 types of SD card depending on their size:
- SD (or full format SD)
- Mini SD
- Micro SD
For a few years, now only SD and micro SD has continued to be on the market. The mini SD is obsolete and completely deprecated.
- SD: it was the first model to appear on the market. It is 32 mm high x 24 mm wide x 21 mm thick. It is currently the most common format between DSLR digital photography DSLR cameras and some camcorders.
- Mini SD: These are the first evolution of SD cards and are 21.5mm high x 20mm wide x 14mm thick. They are currently deprecated.
- Micro SD: Micro SD is the most common format on small devices. They can be found on mobile phones, tablets or consoles. The size of the micro SD is 15 mm high x 11 mm wide x 10 mm thick.
What is a Micro SD card?
Micro SD is a flash memory variant of the Secure Digital type. With permission from Huawei NM Cards, microbes are the smallest memory cards. They are only 15x11x10 mm in size.
Without a doubt, the great advantage of this type of memory cards is its small size. MicroSD allows you to store a large amount of information in a tiny space. Another point in your favour is the current price of these cards, making the price/capacity ratio very high.
What devices use SD or micro SD memory cards?
Despite their long history, SD cards remain the current standard chosen to expand the memory of many devices, such as:
That manufacturers have decided on a card format simplifies it greatly. Not many years ago, choosing a memory card was a bit chaotic. We had a whirling of different types such as Sony Memory Sticks, Olympus CDs, or Compact Flashes (which are still in use today in the professional realm).
Although not all manufacturers currently bet on SD or Micro SD, Huawei uses NM Cards on their high-end phones, and some Sony professional video cameras feature slots for XQD memory cards.
How to Choose the Best Micro SD Memory Card?
To not get too complicated, here are the 4 basic points to keep in mind before purchasing a memory card:
- The type of card
- The Class
- The BUS
- The ability
- The brand
How many types of micro SD cards are there?
Yes, many people think that all micro SD memory cards are the same, and although they actually seem so, there are many differences between them. One of this micro SD purchase guide’s goals is to learn how to differentiate them and buy the most suitable micro SD from your device.
Let’s get in trouble! Currently, on the market, we have 3 types of Micro SD cards in terms of capacity:
It is the oldest micro SD format of the three. This type of card has a maximum capacity of 2 GB. You could say that they are obsolete since 2 GB today are not enough to even for a 10-minute video on a modern smartphone. This format uses a FAT32 and FAT16 file system.
Micro SDHC (HC: high capacity) cards were the next to be released, ranging from 2 GB capacity to 32 GB. They are compatible with SDHC and SDXC devices. SDHC cards use the FAT32 file system, so we can’t write files larger than 4 GB.
SDXC (XC: eXtended Capacity) cards are the third and newest generation of micro SD cards and are probably the type of card you need. These microDS range from 32 GB of memory to 2 TB.
Even though 2 TB is the theoretical maximum of the SDXC standard, the largest micro SD cards for sale when I write this article are 1TB micro SDcards. The file system they use is exFAT, which means that it does not have the limitation of 4 GB per file of the FAT format.
As a curiosity, the largest file stored in an exFAT file system is 16 EB (Exabyte), equivalent to the madness of 16,000,000 TB.
Important! You should know that card revision are backward compatible with each other. That is, the 3 types of micro SD will work in a micro SDXC card slot, while in a micro SDHC card slot, it will only be compatible with standard HC and SD. On devices with micro SD readers, only the first micro SD will work.
When buying a micro SD or SD card, you must also consider its Class Rating. The Class broadly indicates the minimum write speed of a memory card. Knowing the Class, we’ll know easily if it’s fast enough for the device we’re going to use it on.
Distinguishing the Class from a card is simple. In all SD and micro SD, you will see an icon like the one below, a number within the letter “C”.
Sometimes the Class can be confused with the speed of the card. However, a High Class does not indicate that a card is fast; it only indicates the minimum guaranteed speed at which the card will operate, expressed in Megabytes per second.
It has nothing to do with the maximum speed; this figure refers to the minimum speed, which will give us an idea of the card’s performance or know first of all if it is suitable for our device.
My advice is that, to this day, you always look for at least one Micro SD Class 10; although almost all micro SD cards that are for sale are Class 10, there are still slower cards left in stores.
- Class 2:minimum speed of 2 MBps/sec
- Class 4:minimum speed of 4 MBps/sec
- Class 6:minimum speed of 6 MBps/sec
- Class 10:minimum speed of 10 MBps/sec
For not so long, we have new classes: “V” and “A.”
Clase V: Video Speed Class
To increase memory card performance and the requirements of 4K, 8K and virtual reality video recording by 360degrees, the SD Association announced some time ago the arrival of a new revision of the SD standard: Secure Digital 5.0
One of the advantages of this new version is that it supports recording up to eight files simultaneously.
The new SD 5.0 cards will be called Video Speed Class.
The V-Class (or Video Speed Class)was specially designed to distinguish the best SD and micro SD cards to record 4K video and 8K resolution.
Class V is identified by a “V” next to a number. This encrypts the minimum card speed expressed in MB/second. Class types Vision V6, V10, V60, and V90.
- V6: Minimum speed of 6 MB/sec. Ideal for recording videos in standard definition
- V10: Minimum speed of 10 MB/sec. Ideal for recording videos in standard definition and low bitrate Full HD
- V30: Minimum speed of 30 MB/sec. Best for full HD 1080p video recording
- V60: Minimum speed of 60 MB/sec. Ideal for recording videos in 4K resolution
- V90: Minimum speed of 90 MB/sec. Ideal for recording videos in 8K resolution
I leave you this summary box so you can see at a glance the features of the special memory cards for video, the Class V.
Class A: App Performance Class
A Class A SD or micro SD memory card indicates that a card is good enough, fast, and reliable enough to seamlessly install and run mobile apps. The Performance Class App is relatively new terminology and came with SD version 5.1.
Using this type of memory card for tablets and smartphones will make it easier to run applications from the card itself.
There are two
- A1:minimum speed 10 MB/s
- A2: minimum speed 10 MB/s (but with more random read and write speed)
New Class A1 SD memory cards must meet the following conditions, and all manufacturers must secure them on devices that certify with this new specification:
- Input/Output Operations per Second (IOPS) – 1500
- Write IOPS – 500
- 10 MB/s sequential sustained performance
Therefore, what actually certifies a Class A is random read and write speed. Precisely of this type of readings and writes are the ones that most use the operating system of a smartphone, game consoles, etc., small files located along with the card in different places.
UHS: BUS guy
Now that you know what a Class 10, Class V, or Class A memory card is, let’s get on with the BUS.
UHS was created in 2010 and is the way to identify the type of BUS that the memory card has. Okay, but what is the BUS? It is known as BUS at the speed at which communication between the device and the card itself can be made.
Once they reached the Class10 limit, the BUS UHS (Ultra High Speed) was implemented. In turn, other standards were born that we can find today, the UHS-II and UHS-III. The BUS is represented on the card with the number within the letter “U”.
- UHS-I Class 1 or U1 (Ultra High Speed): minimum speed 10 MB/sec
- UHS-I Class 3 or U3 (Ultra High Speed): minimum speed 30 MB/sec
In this table, I show you the types of BUS that exist so far, along with the maximum speeds that each one supports.
To be able to handle that high amount of data per second (much higher than a SATA HDD can handle today), the UHS-II and UHS-II micro SD have a row of new pins or connectors on their back. These additional connections increase the available bandwidth to 150-300 MB/s.
The UHS-II and UHS-III memory cards are backward compatible with UHS.
How much capacity should I buy the card? The short answer is: it depends
Today a 32 GB card is usually the least my customers are looking for. Phones with 64 GB of internal storage have already been set as standard, so the best-selling memory cards start at 64 GB. They are currently the best choice in storage/price ratio.
The long answer is that the card’s size depends on the type of material you want to store and especially the amount. If you’re looking for a photo memory card, you should look for a card that stores between 1,500 and 2,000 images from any camera you currently have.
Megabytes vs Megabits
When we talk about speed in memory cards’ characteristics, we always mean MB/s (megabits per second). Do not confuse this measure with Mb/s (megabits per second).
Memory card manufacturers typically measure their cards’ speed in megabytes per second, or MB/s (or MBps, both with a capital “B”). But video recording speeds are usually measured in megabits per second, or Mb/s (or Mbps, with a lowercase “b”). They’re not the same.
A byte consists of 8 bits, so to move from megabits per second to megabytes per second, it is multiplied by 8. Therefore, if we take the calculator, we will know that 80 MB/s equals 640 Mb/s.
How many photos or minutes of video can I save to each card?
Let’s say your new smartphone has a 12 Megapixel camera. Jpg will be on average 3.5 MB in size, so for an X GB card, you can store X photos:
- 2 GB – 250 approx.
- 4 GB – 500 approx.
- 8 GB – 1000 approx.
- 16 GB – 2000 approx.
- 32 GB – 4000 approx.
- 64 GB – 8000 approx.
- 128 GB – 16000 approx.
But if you want to record video, the average size of a video clip in Full HD1080p resolution at 25/30 fps, you can store X time:
- 2 GB – 2 minutes approx.
- 4 GB – 5 minutes approx.
- 8 GB – 10 minutes approx.
- 16 GB – 20 minutes approx.
- 32 GB – 40 minutes approx.
- 64 GB – 80 minutes approx.
- 128 GB – 160 minutes approx.
SanDisk offers us on its website this summary table of capabilities.
Best Brands of SD and Micro SD Memory Cards
Why is marking a memory card important? Because, sadly, there are a lot of cards on the market that falsifying your data and even falsifying prestigious brand cards.
In this almost, paying for the brand is worth it. A card from a good manufacturer assures us of a certain quality and guarantee.
Some of my favourite manufacturers are:
These brands’ cards have earned their reputation by always meeting expectations, even on many occasions delivering higher transfer figures than advertised.
Understanding SD cards
One minute! What do all those symbols, numbers, and letters mean?
Everything we’ve seen during this article is reflected in the cards themselves:
- Maximum reading speed: This is the maximum reading speed of the card. It is typically expressed in megabytes per second (MB/s). Keep in mind that the speed the cards set are maximum transfer spikes and can rarely maintain these speeds for long periods of time.
- This is another, perhaps outdated way to express the maximum reading speed: it is based on the read speed of audio CDs, 150 KB/s. To know the speed of a memory card, you only have to convert, for example, 1000x to KB/s. This is done by multiplying 150 by 1,000. The result will be given in KB, so by dividing by 1000, we convert KB/s to MB/s. In this case, 1000x equals approximately 150 MB/.
- Type: This indicates the type of card. Different card types use different file formats, and new cards will not work on older card readers.
- UHS Speed Class Classification: This is the minimum sustained write speed of the card. This data is essential when looking for a card for video recording, for example. UHS Speed Class 3 cards will never write at less than 30 MB/s; UHS Speed Class 1 cards will never be slower than 10 MB/s.
- Speed Class Classification: This is one way to rank the oldest speed. It is redundant of the UHS speed class, as it also indicates the minimum sustained write speed of the card. Many card manufacturers also include it, as many consumer products still recommend products based on the above standard. Class 10 is the old speed class level, and it is verified that a class 10 card never writes slower than 10 MB/s, and for example, class 4 would never be slower than 4 MB/s.
- UHS Classification: A card’s UHS rating determines the maximum speed of the bus a card can read at, assuming that the memory on the card is fast enough to match. Non-UHS cards have a maximum of 25 MB/s, while UHS-I cards support up to 104 MB/s. UHS-II cards support up to 312 MB/s. Both the card reader and the card must be compatible with the same standard to benefit from increased speed, but UHS cards are backward compatible with older readers; they simply won’t be as fast on them.
- Capacity: This numbering indicates the capacity of the card. SD cards have a range of up to 2 GB, SDHC cards range from 2 GB to 32 GB and SDXC cards from 32 GB to 2 TB.
How does a micro SD card work?
SD cards have many advantages over other storage systems.
Micro SD cards differ from other flash drives because it is possible to write about the thousands of times without being damaged. Another advantage is that they don’t need the power to maintain data (non-volatile memory). Instead, other memories, such as RAM, do need power (volatile memory).
They are reliable and ideal for portable devices because they don’t have moving parts, such as SSDs, so there’s no risk of data loss from shock or vibration.
In other words, in a way, they’re like small SSDs, albeit with lower performance.
The above features make them ideal for smartphones, digital cameras and other devices that need portability, ample storage space and resiliency.
As with SSDs, data from an SD card is stored in a series of electronic parts called NAND chips.
These circuits allow data to be recorded and stored on the memory card. And since there are no moving parts, the data can be transferred at high speeds to and from the card, far exceeding the speeds of CDs/DVDs or HDDs.
History of SD cards
If we go back to the beginning, everything is born from Toshiba when in the late 80’s it launched NAND architecture for memories. No doubt this was the germ of a great revolution in the world of storage.
It was not until 1997 that Siemens and SanDisk teamed up to design the MMC or Multimedia Media Card, a 24 mm x 32 mm x 1.4 mm card that originally used a 1-bit, 7-pin serial interface. Several issues made it popular on a large scale. On the one hand, their characteristics and dimensions, and on the other, the fact that companies did not have to pay royalties if they wanted to add an MMC card to their products. Maybe this was the determining factor.
Meanwhile, in the portable storage landscape, Sony released its well-known Memory Stick, Olympus and Fujifilm developed the XD-Picture Card, and Toshiba creates the Compact Flash. All these cards and technologies coexisted for years. Each manufacturer bet on a standard, however, and over the years, the SD format was the clear winner and prevailed against the others as a storage standard.
SD card is born
It looks like it was yesterday, but the Secure Digital card standard is now of legal age. It was released in 1999 and was developed by several companies, including SanDisk, Panasonic and Toshiba. Today the standard is run by the SD Association (SDA).
Considering their size, we can find 3 types of SD memory cards, although some have already been deprecated:
- SD: was the first to be released to the market. Its dimensions are 32 millimetres high x 24 millimetres of
- MiniSD: the second evolution, and almost extinct already, is 21.5 millimetres high x 20 millimetres wide x 1.4 millimetres thick. Its weight is 0.8 grams.
- MicroSD: without a doubt, the most popular format. Its dimensions are 15 millimetres high x 11 millimetres wide x 1 millimetre thick. Its weight is 0.3 grams.
The first SD on sale
A year after its release, in 2000, the first models available in 32 MB and 64 MB are released. Today we would barely keep a couple of photos in them, but they were a breakthrough for their time. Its dimensions are 24 mm x 32 mm x 2.1 mm, and its weight approximately 2 grams. It has 9 pins and mechanical protection against writing. Its operating voltage varies between 2.7 and 3.6 v.
Did you know that the SD card logo is a variant of Toshiba’s logo for the DVD?
Mini SD: an announced failure
In 2003 SanDisk introduced a smaller standard in CeBIT 2003 compared to the original SD. The miniSD card comes out. With a size of 20 mm x, 21.5 mm x 1.4 mm, and 1 gram in weight, the SD Card Association or SD Association (SDA) recognizes it that same year as a small size extension for the Secure Digital card standard. It loses the write lock relative to the original SD. Its operating voltage is maintained at 2.7 and 3.6 v. Despite this, manufacturers did not bet on this format, and this version was considered a failure.
Micro SD: the current standard
However, the case of microSD (also called T-Flash, TF or TransFlash)was different. This format was born in July 2005 by SanDisk with about 15 × 11 × 1 millimetre thick and weighing just 0.8 grams.
The first models had capacities of 8, 16, 32, 64 and up to 128 MB. The high demand for digital content storage drives, creating a new format: the MicroSD SDHC (High Capacity). But the need to increase the current speed rates of the time and the size of the memories later gave birth to the MicroSD SDXC (eXtended Capacity), with its up to 2 TB capacity and a Bus that reaches vertigo speeds, higher than even that of SATA hard drives and close to 300 MB/sec. Time set this card as the current storage standard.
SD Express: the future
The future passes through the SDUC or SD Express. This revision corresponds to SD 7.0 and is expected to be released in the first quarter of 2022. Some voices place them as replacements for today’s SSDs due to their maximum capacity of 128TB and transfer speeds of up to 985 Mb/sec.
If you want to learn more about the SDUC and MicroSD Express, check our article on SD Express cards.
Evolution of SD or Secure Digital cards
Over the years, several different SD cards have evolved in parallel:
Unlike traditional SD, the SDIO standard was not designed to store information but to connect that allows information to be transmitted. It maintains the same size as the SD card. It allows you to integrate small accessories, such as GPS receivers, Wi-Fi or Bluetooth adapters, modems, barcode readers, IrDA adapters, FM radio tuners, RFID readers or digital cameras.
Integration with other devices such as RS-232 series adapters, TV tuners, fingerprint scanners, magnetic stripe readers, Bluetooth/Wi-Fi/GPS, ethernet adapters and PCS, CDPD, GSM, etc. modem adapters have been proposed but have not yet been implemented.
SD cards with Wi-Fi
The most well-known Wi-Fi SD cards are undoubtedly Eye-Fi. These cards of up to 8GB capacity have the peculiarity that integrates a Wi-Fi chip inside, so that together with a Software allows to communicate wirelessly and directly with other computers such as PCs, laptops, tablets or smartphones, and thus provide Wi-Fi connectivity to the cameras where they are used. The new Eye-Fi Mobi Pro adopts the SDHC standard and is available in 16GB and 32GB. The Eye-Fi Pro X2, the first SD card with 802.11n WiFi.
Other manufacturers such as Toshiba also released Wi-Fi-connected SD cards, Toshiba FlashAir, and 3 16, 32 and 64 GB drives are available in their catalogue, respectively.
SD vs Compact Flashcards
Traditionally, SD cards were always a few steps away from Compact Flashcards in terms of performance, but because Compac flashcards have not been updated for some time, SD cards were recently passed with UHS-II cards.
UHS-II SD cards offer read speeds of up to 312 MB/s, almost twice the UDMA 7 CompactFlash cards’ speed. However, because they are so new, there are not many cameras and card readers compatible with UHS-II cards, and while UHS-II cards are backward compatible, they won’t work at full speed with older card readers. In fact, most high-end DSLR cameras still cannot write at UHS-II speeds.