Twelve Different Classes of Memory Cards Explained

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Twelve Different Classes of Memory Cards Explained

While memory card class is often defined only in terms of speed it can also be important to look at the other two aspects which are also considered classes, namely, physical size and capacity. All three classes will come into play when selecting a memory card for a phone, camera, or other mobile unit. The three different aspects of a card can be intermixed, so it is important to choose the most suitable card for any device although adapters can sometimes be used.

The Three Aspects of Memory Cards Explained

Physical size or format refers to the shape and appearance of the memory card and will be standard, mini, or micro. Capacity is concerned with how much can be stored on a card with the lowest usually being 2GB and the highest very occasionally reaching 1 or even 2T. The third aspect is often the most confusing for many users and deals with speed, i.e. how quickly the card interprets and stores data. Cards are often referred to as flash memory cards or SD (secure digital) memory cards.

Different Class Sizes or Physical Formats of Memory Cards

One of the most important things to consider when purchasing a memory card is that it will fit in the device it is required for. When buying a new device the card size will nearly always be stated in the instruction manual, but when a manual is not available it can be useful to check the size of the memory card slot. A standard size SD memory card is 32mm x 24mm x 2.1mm and is more likely to be found in older model phones or a variety of cameras. Mini SD cards are 21.5mm x 20mm x 2.1mm. The mini SD card is smaller than a standard size but larger than a micro SD card and is the most infrequently used size. Micro SD memory cards are most commonly found in mobile phones and sometimes in cameras and measure 15mm x 11mm x 1mm.

Standard size SD memory card

Usually available in either 2GB, 4GB, 8GB, 16GB, 32GB, or 64GB. Prices tend to go up in conjunction with memory type and speed. Various speeds can be found on a standard card although the very high class speeds are less common. A standard size card is also recognisable by the cut off end which is used to help orient the card correctly in a device. Most often used in cameras but some phones are also designed to take this size. Blue and black are the most usual colours. Older computers often have a card reader designed to specifically read a standard card so it can sometimes be useful to use an adapter to transfer data from a smaller card to a standard SD card. Some cards may be sold together with an adapter.

Mini SD memory card

Available with a range of memory size although it may be harder to find mini cards with more than 32GB of memory. Always check for compatibility with device.

Micro SD memory card

Readily available in a range of capacity and speed combinations. The majority of modern phones are now designed to accept a micro SD card due to the small size and light weight. While 2GB, or even less, memory can be found on some cards it is more common to find micro cards in the higher end ranges. Speed classes also vary.

SD memory card sets and adapters

Many sizes of SD cards are sold in sets of two or more. Useful for those using a lot of data, more data than a device will accept, or more than one device at a time. Adapters can be used to make data available for a device that requires a different type of card.

Memory Card Capacity or Memory Class

While it would seem obvious that purchasing a card with the largest possible capacity is the best way to go, this is not always the case. Some phones or other devices will only accept cards up to a certain GB level. When this is the case it makes more sense to buy more than one card to record and store data. Apart from this, higher capacity allows the user to store more information or larger files.

128MB SD card

Becoming more difficult to find and usually now used as a back up or for those seldom need memory. More likely to be found in standard sized cards.

2GB SD card

Often supplied free with devices. Useful as a back up or for small data storage. When keeping as a back-up it pays to have a plastic storage case.

4GB – 64GB SDHC cards

SDHC stands for Secure Digital High Capacity. Some cards up to around 16GB will be labelled simply as SD but are in fact SDHC. Note that some older devices are not able to take SDHC cards. Suitable for the majority of modern phone, camera or other devices. Select according to individual needs and accompanying card format and speed.

64GB – 2TB SDXC cards

SDXC stands for Secure Digital Expanded Capacity. Many older devices will not accept SDXC so it always pays to check for compatibility. Readily available in 64GB capacity but higher memory can also be purchased. SDXC cards will usually also be combined with a high speed class. Suitable for those wishing to store large professional quality files.

Speed Classes for Memory Cards

Speed is defined by how many Megabytes per second (MBps) are transferred. The higher the speed is the better the image definition will be. Higher speeds are also useful for taking a succession of quick pictures. Five speed classes are readily available although many devices are only capable of accepting cards up to a certain speed. As technology improves, more devices are becoming available that will take higher speed classes. It should be noted that some brands define the MBps speed differently.

Class 2

Slowest speed. Suitable for general snapshots and standard definition video recording.

Class 4

May be 4MBps or 15MBps data transfer rate depending on brand. Check for compatibility with older devices.

Class 6

Offers 15MB or 20MBps data transfer depending on brand. Useful for above average picture quality.

Class 10

Offers 30MBps or 40MBps data transfer speed depending on brand. Very suitable for recording high definition video. Check that device is able to accept this class.


Ultra high speed delivering 45MBps data transfer rates. Usually only suitable for the most up to date devices. Used for highest quality recording of data.

Coming up

It is anticipated that SD cards will become available that may be able to offer up to 310MBps as devices are developed that can deal with this kind of speed.

Finding Flash Memory Cards on eBay

Starting at the Mobile Phones and Communications category of eBay it is a simple matter to click on the memory card subcategory on the left and browse from there. Depending on the class of card required, using the left hand directory can help to narrow a search according to physical format and capacity. When searching for a specific speed class it may be necessary to type in the class required in the advanced search box at the top of the page. Alternatively, physical size and capacity can be selected and each listing checked for speed class. Using the question section on individual listings can also be useful for ensuring the memory card has all the desired qualities.


Combining different classes from each aspect of a flash memory card can usually result in finding the right card for the right purpose and device. All the aspects come together to deliver the final performance and all can be mixed and matched. As previously stated, it is of paramount importance that the device to be used is capable of accepting whichever type and class of card selected.

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