Dual card slots

Many digital SLRs aimed at keen amateurs and professionals have two memory card slots, and this is not just to increase the overall storage capacity.

Then can be used for this, of course, but high-capacity memory cards are cheap these days, and storage space isn't the problem it was.

Some cameras use dual slots to offer support for two different card formats. This Nikon D-SLR can take both SD cards and Compact Flash.

Instead, you can use the two card slots to store different types of data which you want to keep separate. Depending on whether the camera supports it, you could do the following:

• Save photos to both cards at the same time so that you always have a backup in case one memory card fails or gets lost

• Use one to store RAW files and the other to store JPEGs (for cameras which offer simultaneous RAW/JPEG shooting)

• Use one card to save photos and the other to save movies

xD Picture cards | On the verge of extinction

The xD Picture card format was developed by Olympus and Fujifilm but has never really caught on and there are signs that it's now on the way out. When it came out, it was the smallest memory card format available, but today's MicroSD cards are smaller still, so the xD format has no real advantages any more.

For a while, Fujifilm cameras came with combined xD/SD memory card slots so that owners could use both types, but the latest cameras use SD cards only. Olympus, meanwhile, still uses xD card slots in its compacts but now provides a MicroSD adaptor so that owners can use MicroSD cards instead.

Eye-Fi cards | Wireless connection for your camera

Eye-Fi cards are SD memory cards which contain a built-in wireless transmitter. Providing you’re within reach of a suitable wireless hotspot, you can then transmit your pictures to a photo sharing site or, if you’re at home and have a wireless router, you can send them to your computer.

Eye-Fi Explore cards can also ‘geotag’ your photos. This isn’t done directly within the camera, though – the location information is added to the photos later using software on your computer. Eye-Fi cards don’t contain a conventional GPS receiver. Instead, they look for nearby wireless hotspots and use a service called Skyhook to look up their location.

As a result, coverage is variable and probably not as reliable as conventional GPS right now. It’s quick and simple, though, and as the Wi-Fi card demonstrates, the technology can be fitted into a tiny space.

Eye-Fi cards are very clever, but make sure you camera is Eye-Fi compatible before you invest.

Micro SD | The same but smaller

Micro SD cards are the tiny memory cards found in most mobile phones. What's surprising is not just the tiny size, but the fact that they're available in much the same capacities as standard SD cards and at similar prices.

This 4Gb Micro SD card looks big enough here, but is actually the same size as your little fingernail. So why should Micro SD cards find their way into cameras? Olympus seems to have accepted that its xD Picture card format has a limited future, and in its latest compacts it includes an xD/Micro SD adaptor. The adaptor's in the shape of an xD card (which Olympus compacts still use) but it has a slot for pushing in a Micro SD card.

It's a smart move because these are cheaper and more plentiful than xD cards. For example, a 4Gb Micro SDHC card currently costs £10 or less.

But instead of getting a Micro SD card on its own, look out for adaptor bundles like the Kingston 'Mobility' packs. The pack illustrated includes a 4Gb Micro SD card, a standard SD adaptor (so that you can use it in cameras that use standard SD cards), a Mini SD adaptor (which may be more useful in the future) and a USB stick adaptor, so that you can use your Micro SD card as a USB flash drive. Ours cost £16 from Staples, but you can probably do better.

SDXC cards

SDXC is the latest generation of the SD card format, and boasts even higher capacities than SDHC and faster read/write times. They are ideal for HD movies, but they are expensive.

SDXC cards can have a capacity of 32Gb right up to a theoretical 2Tb (2,000Gb). Their application for stills photography may be limited, but they are perfect for the latest generation of solid-state HD movie cameras.

Panasonic has announced (January 2010) two new SDXC cards in 48Gb and 64Gb capacities. These cards are, however, fearsomely expensive compared to regular SDHC cards, though presumably prices will fall eventually. They can store over 6hrs and 8hrs respectively of high-quality full HD footage and are designed for the company's latest HD camcorders and cameras like the Lumix GF1 (above), though there is currently some doubt whether the GF1 (or Panasonic's full HD GH1) will be SDXC-compatible without a firmware update.

Panasonic's latest SD camcorders and compacts do take SDXC cards, though, and it seems likely that the format will be taken up by other makers too.