Memory card FAQ: all your questions answered

When it comes to memory cards, it's easy to become confused thanks to all of the different types and variations available. Whether using them in mobile phones, cameras or TVs, here's CNET Australia's guide to memory cards.

When it comes to memory cards, it's easy to become confused thanks to all of the different types and variations available.

Memory cards are used in a range of devices, from cameras and camcorders to mobile phones, televisions and consoles. Knowing what type of memory card is right for you (and your particular devices) is becoming vitally important, and this is where we can help.

What is a memory card?

Memory cards are small devices (some no bigger than your thumbnail) that are used to store electronic data. This can be anything (depending on the device) from photos, music, movies, games, documents, programs and more. While cards come in a variety of shapes and sizes and are available for a variety of products, all memory cards do essentially the same thing — store data.

Memory cards, also referred to as flash memory, are essentially chips that allow users to write and rewrite data multiple times. Some of the key features of flash memory cards include their small size and the ability to retain data without a power supply. This allows them to fit into a variety of portable consumer devices.

What types of devices need memory cards?

Devices like the Nintendo Wii use SD cards. (Wii console SD card image by Evan Amos, public domain)

Memory cards first took off as the storage medium of choice in photography, with cameras dispensing with film rolls to instead rely on the much smaller and cost-effective memory cards. As well as digital cameras, memory cards are commonly used in mobile phones to store information like photos and music, as well as in camcorders to store video.

Memory cards are also used in other consumer electronic devices such as televisions, portable game devices, printers, DVD recorders and more. Many TVs come with card slots which allow users to see any stored photos on a big screen, while some printers allow you to print directly from images stored on a card.

While you can easily swap cards from one product to another, it's important to remember that different devices take different types of memory cards. If you already have a device that takes a memory card and want to buy more gear, make sure your intended purchase can take the same type of card.

What are the different types of memory cards available?

Over the past few years the number of different types of memory cards has reduced drastically, due to standardisation. The main types currently available include SD, Memory Stick and CompactFlash. Other, less common varieties in older devices include MMC, xD Picture Card and SmartMedia.

Secure Digital (SD) is the most widespread format, and come in various different capacities and speeds. Memory Stick is a proprietary format developed by Sony and as a result is found mainly in Sony devices. CompactFlash is a standard specifically developed for digital cameras and is now most commonly used in higher-end SLRs. The xD Picture Card is being phased out, a proprietary format developed by Fujifilm and Olympus.

Some cameras come with dual card slots. (Credit: Nikon)

Devices will usually only take one variety of memory card, although some cameras and camcorders have a single slot that accepts two different varieties of cards, such as Sony cameras, which generally take SD and Memory Stick. High end digital SLRs may also have two or more slots for different types of cards, such as the Nikon D300s, which has an SD and CompactFlash slot side-by-side.

Many formats also have sub-variants. SD, for example, also comes in miniSD and microSD (also known as TransFlash) forms, while Memory Sticks have the Memory Stick Pro Duo variants. While the underlying technology is the same, the size and form factor is vastly different in these variants.

Can I use the same card on other devices?

Even though the packaging suggests it's used for cameras, you can still use this SD card on other compatible devices. (Credit: Lexar)

The simple answer is yes, but with some caveats. As long as your different devices take the same type of card, you should be able to freely use the same memory unit in those different devices. If, for example, your mobile phone and laptop all take SD cards, then you'll be able to use the same SD card to store data, take pictures or transfer information.

You may not be able to access or use your stored data from one device to another, however. Individual devices may use a specific file structure when recording information onto a memory card, or they may use specific file format types. If a device is unable to browse a memory card's directory or cannot read a specific type of file format, then it won't be able to display or utilise something stored using a different device. Songs stored as MP3 files on a card, for example, can't be played on a device that doesn't have MP3 support.

Also worth noting is that older devices that use regular SD cards may not be able to read the newer SDHC and SDXC cards, even though the form factor is exactly the same.

How safe is the data stored on memory cards?

When it comes to the safety of your data, memory cards have some key advantages over other storage devices such as hard disks or CDs/DVDs. Memory cards are much more shockproof than other storage mediums. Since there are no moving parts in a memory card, they're much less prone to damage from movement, which can occur in a normal hard drive.

They're also much less fragile than a CD/DVD. The case of a memory card can easily take a scratch or two, while scratches on the underside of a CD or DVD will most often result in data loss or an unreadable disk. Since memory cards are physically so small, perhaps the greatest risk of data loss lies with losing the entire card itself, rather than by some other accident.

SanDisk's all-in-one reader can take all major types of memory cards. (Credit: SanDisk)

How do I transfer data from my memory card to my PC?

Most portable devices come with cables to link directly to a PC or laptop, allowing you to transfer any images or data stored on your memory card. If you don't have your device or cable with you, however, there are other alternatives.

The majority of new PCs and laptops are now being sold with built-in card readers. These allow you to slide your card directly into the computer, from which you can access any data stored on the card. There are also stand-alone card readers you can purchase. These card readers can usually read more than one type of card, which is handy if you've got several devices with different memory units.

Secure Digital (SD)
Secure Digital High Capacity (SDHC)
Secure Digital Extended Capacity (SDXC)

SD cards all have the same form factor, but different labels depending on its type. (Credit: Lexar)

The postage-stamp-size SD card is the most popular type of memory card on the market. Its small size, large capacity and robust design has made it common in everything from cameras to MP3 players. Other advantages include relatively high-speed data transfer and a mechanical write protect switch to protect data.

While not readily available in Australia, Eye-Fi cards are wireless SD cards that can automatically upload images to your PC or photo-sharing services over Wi-Fi.

SD cards also come in a range of speed variants. This is often displayed on the card itself as a class rating in a small circle, ranging from Class 2 to Class 10.

Class Best used for Minimum write speed
Class 2 Standard-definition video recording, general stills photography in compact cameras 2MBps
Class 4 HD video recording, continuous stills photography in compact cameras 4MBps
Class 6 Full 1080p video recording, continuous and regular stills photography in high-end compacts or ILCs 6MBps
Class 10 Full 1080p video recording, professional camcorder or continuous high-resolution stills in SLRs 10MBps

Table data taken from Lexar white paper Understanding SD Association Speed Ratings.

Faster speed ratings means your memory card is quicker to recover after data is written to it. This is especially important for photography — having a fast memory card means you're able to take another shot quicker than usual, particularly for higher megapixel models. The performance of an SD card is also dependent on how fast the host device (eg, camera or memory card reader) can read and write data.

The symbol you will see on UHS cards. (Credit: Integral Memory)

Another method of classifying an SD card's read/write speed is by using the UHS-I (Ultra High Speed) classification. These cards have a bus speed of up to 104MBps. The UHS-II specification has recently been announced, which can achieve bus speeds of up to 312MBps, but there are no cards using the technology available at the time of writing. UHS cards are backwards compatible with non-UHS devices, but will not be able to achieve the UHS speed.

A diagram showing how the different types of SD cards are backwards compatible with devices.
(Credit: SD Association)

CompactFlash

CompactFlash used to be quite prolific in the camera realm, but is now reserved mainly for high-end digital SLRs. CompactFlash cards are hardy: the cards have an operating shock rating of 2000Gs, which is equivalent to a 3.3m drop, and can withstand rapid changes in temperature in a range from -40 to 85 degrees Celsius.

(Credit: SanDisk)

There are several varieties of CompactFlash cards: Type I and Type II. Type II cards are slightly thicker than type I cards. While you can use a Type I card in a device that has a Type II slot, Type IIs are usually too thick to fit into a Type I slot. Most cameras that use CompactFlash only accept Type I cards.

CompactFlash cards also have speed ratings, though it is displayed differently to SD cards. Speed ratings are classified as 133x, 300x and so on, which is the same way of classifying CD-ROM speeds. For example, 133x is equivalent to 20MBps, 300x is 45MBps, 400x is 60MBps and 600x is 90MBps. CompactFlash cards can also be labelled as UDMA, which stands for Ultra Direct Memory Access. Cards classified as such are able to achieve much faster read/write speeds than non-UDMA cards.

CompactFlash cards are typically available in a range of capacities and speeds up to 128GB and 600x.

Memory Stick

(Credit: Lexar)

A proprietary format developed by Sony, Memory Sticks can be usually found in Sony's range of consumer electronic devices. Since their introduction, there have been several iterations and form factors. Now, Sony has consolidated its Memory Stick format into two main lines: Memory Stick Pro Duo and Memory Stick Pro-HG Duo.

While you can use older Memory Sticks in new devices, only products that are Pro compliant will be able to use Memory Stick Pro units. Duos are smaller versions of Sony's Memory Sticks. Duos have all of the features of the larger Memory Stick, and also come in Pro versions. Duos need an adapter to fit into normal Memory Stick-enabled devices.

(Credit: Sony)

The Memory Stick Pro-HG Duo was developed by SanDisk and Sony to have fast read/write speeds, three times faster than the original Pro cards and comes in capacities up to 32GB.

Memory Stick Micro was Sony's answer to the microSD card, but has since been dropped from Sony Ericsson phones in favour of microSD.

miniSD

miniSD cards use the same technology as SD cards, meaning users get all of the advantages of an SD but in a smaller package. These smaller SD cards are used in devices such as mobile phones and MP3 players. They are often sold with an adapter, which allows you to use the card in a normal SD slot or USB port.

(Credit: Kingston)

microSD

An even smaller SD variant, the microSD format is currently most popular with mobile phone manufacturers due to its extremely small size. They're almost too small to comfortably hold and swap in and out of devices — be careful when you're handling these little units. Like regular-sized SD cards, these are available in microSDHC and microSDXC variants.

xD-Picture Card

(Credit: Fujifilm)

The xD-Picture Card is yet another proprietary memory card format, this time developed by Olympus and Fujifilm for use in their digital photography products. xD-Picture Cards have been designed to minimise power consumption and therefore save battery life. Very few new cameras are designed to be compatible with these cards, making xD a legacy format.

How much can I fit on a memory card?

How much you can store on your memory card depends on three factors: your device, what type of data needs to be stored and the quality of that data.

High megapixel cameras, for example, need more memory space per shot than low megapixel models. The type of data being stored also determines how much you can fit on a memory card. Images take up more room than text documents. Digital music takes up even more, while video is another space hog.

The quality of your files is the final determinant in how much you can cram onto a memory card. The general rule is the better the quality, the more space it will take. High resolution photos, for example, require more memory space than low resolution shots. If you are shooting in RAW mode on your camera, each file requires a lot more space than a regular JPEG image. Music compressed at a higher quality (otherwise known as bitrate) will also take more room than something with average compression.

The table below shows the approximate number of JPEG images (100 per cent quality) able to be stored on a memory card.

Megapixels File size 1GB card 2GB card 4GB card 8GB card 16GB card 32GB card
6 megapixels 1.8MB 476 953 1907 3814 7629 15,258
8 megapixels 2.4MB 357 715 1430 2861 5722 11,444
10 megapixels 3MB 286 572 1144 2288 4577 9155
12 megapixels 3.6MB 238 476 953 1907 3814 7629
14 megapixels 4.2MB 204 408 817 1634 3269 6539
16 megapixels 4.8MB 178 357 715 1430 2861 5722
22 megapixels 6.6MB 130 260 520 1040 2080 4161

Table data taken from SanDisk.

Lexar's website has a tool that calculates how much data a range of files will take up on your memory card.
(Screenshot by CBSi)

Memory card tips

1. Don't buy the wrong memory card type
Make sure you know exactly what type of memory card your digital camera, mobile phone or games device uses before you hand over your cash. Devices will more often than not be only compatible with one type of memory card, which means you're stuck if you inadvertently buy the wrong one. Check your device to see exactly what you'll need.

2. Don't rely on the device's included memory
Some devices come with bundled memory cards, which means you can use the product straight out of the box. But in most cases these bundled cards are at the low end of the capacity spectrum, meaning you won't be able to store too much information on them before having to free up some space.

3. Let your hardware determine the size of memory card you buy
Memory cards with large capacities are not only more convenient, they're practically mandatory for some devices. For example, cameras that can record full HD chew up more memory space per video.

4. Not all memory cards are the same
You'll find plenty of manufacturers out there selling memory cards, all with similar-looking products and claiming similar capacity and performance. Not all memory cards are equal; cards can be made from varying quality components and manufacturing standards. If you've bought a cheaper generic card before and have had no problems, then by all means stick with it. Otherwise, stay with cards from recognised brands sold through authorised dealers. Counterfeit memory cards are also an issue when buying from sources such as eBay.

5. Take care of your memory cards
Flash memory is more hardy than many other forms of storage, but still requires a little TLC to protect your data. Always format a new or pre-used memory card in your camera before using it to take photos. Some cameras won't work if the card has been formatted in another device. Keep memory cards in a case when not in use, and don't remove the card while the device is still switched on or writing data to the card.

If you ever have trouble accessing your images or accidentally delete your photos, our video below will help you recover them.

6. The more the merrier
If you're going away on holidays (or are just an avid user of technology), then there's no reason to stop at just one card. Flash memory is relatively cheap, so stock up on cards before going on an overseas adventure. Depending on how good you are with backing up data on the road, it's also advisable to buy several smaller capacity cards (such as 4 or 8GB versions) rather than storing all your shots on just one 32GB model. This is just in case the card gets lost, stolen or corrupted, because the last thing you want is to lose all your photos in one go.

 

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