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What is an SD card and what does it do?

With all our photos, apps and games, if there's one thing we never seem to have enough of on our smartphones, it's space! However, a lot of devices get around this issue by allowing the use of memory cards, which these days you can get in a range of sizes.

For mobile phones and tablets, the type of memory card you'll need is a microSD. Cards of this type are barely bigger than your fingernail, but can store enormous amounts of data.

Samsung Micro SD card
Samsung produces a range of high-capacity, waterproof storage cards.
Image by SoMobile

Inside every SD card, rows of tiny memory chips are at work – storing all your documents, music, photos and more. And because there are no moving parts, it's all done quickly and effortlessly.

This lack of moving parts also means that microSD cards can be pretty durable: many of the current products on the market even claim to be waterproof.

Samsung, for example, claims that its microSD cards are safe from all kinds of water damage. The company also claims that the cards can survive being run over by a 1.6 tonne vehicle, or withstand the magnetic forces exerted by a an MRI scanner!

How does an SD card work?

As soon as a memory card is plugged into your phone, it gets straight to work. In most cases, your phone will automatically begin to scan the card, pull all the information it needs straight away and file it in the proper place for you.

Android phones, for example, will look for any pictures you have stored on the card – no matter what format they're in – and add them to your gallery. This means you won’t have to search for long to find that photo of a cat in dungarees you took last week. Helpful, eh?

microSD card
If you want to increase your phone's memory or invest in small, secure backup storage, a microSD card should be ideal.
Image by bigcityal

However, you do need to be careful when removing your memory card, and ideally you'll only have to remove it when changing phones. When your phone is actively accessing the memory card, everything on it is a little more vulnerable than usual. If the connection is broken, you can end up with only half the file it wanted to transfer – and more often than not, the card won't know how to deal with it.

This can lead to your pictures not opening correctly, some of your applications crashing or even just a really sluggish phone. Preferably, you should only remove your memory card only when the phone is switched off completely – but at a stretch, many phones have an 'unmount SD card' option in their settings somewhere, so you can switch them when needed.

As time goes on, cards with more and more capacity are coming out – and with mobile cameras increasing in megapixel size and apps and games getting bigger all the time, you really need all the storage you can get.

Luckily, you can easily pick up microSD cards that are up 128GB in size – and some specialist cards are even bigger. At the lower end of the scale, 64GB ones are pretty cheap these days too – so if you're looking to expand your device's memory or invest in small and secure backup storage, the humble microSD card could be just the way to go!


SD Cards – Frequently Asked Questions

Since putting this article together, a number of readers have contacted us with questions concerning SD cards – so we've put together a few answers!

What’s the maximum memory card I can use with my device?

Officially, this varies from device to device – it’s typically either 32GB or 64GB according to device manufacturers. To find out for sure, head over to the GSMArena website and search for your device there: its maximum SD card size will be listed in the ‘Memory’ section.

But in practice, this is only a guideline. According to some independent testers, just about any device with a microSD slot should be compatible with cards up to 128GB.

Can I restore deleted files from an SD card?

Unfortunately, this isn’t always possible – but if the files were deleted recently and you haven’t used the card since, you may be able to recover some of the data with a tool like Recuva, by Piriform. While data recovery is extremely hit and miss at times, it's always worth trying something free like the app above just in case.

Can I save apps to my SD card rather than my phone’s memory?

For newer devices, running Android 4 or above, this option is sometimes available – but it has to be enabled by the app developer.

To find out whether a certain app can be moved to your SD card, go into your phone’s Settings menu, then tap Applications. From there, choose the app you want to move – if it’s possible, you’ll see an option labelled Move to external memory. To move it back to your phone, go through the same process and tap Move to phone.

Can someone read my emails or text messages if they remove my SD card and put it in another device?

No – emails and texts are stored in your phone’s internal memory and cannot be transferred. But they may still be able to access any photos, videos, music and app data stored on the SD card.


Hopefully this should answer any questions you have about using SD cards – but if you need any further assistance, drop us a line in the comments below and we'll do our best to help!

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