If you think that memory cards are those slips of paper that helped you revise for your O-Levels, you're missing out one of the greatest inventions of the last decade.

Slivers of plastic no larger than a book of matches, memory cards can hold as much information as 150 floppy disks, making them indispensable for the modern computer buff. They have no moving parts, can stand up to all kinds of harsh treatment and are used in everything from digital cameras to MP3 players to mobile phones.

That's the good bit. Unfortunately, there's also a bad bit. While using a memory card is as easy as sticking it in a slot, buying one is far more complicated. The problem is that manufacturers simply can't settle on a standard and, as a result, there are currently nine different types of card available, and a gadget that uses one type usually can't use another.

Don't panic, though: Computeractive is here to help, with a guide to every type of memory card currently on the market.

THE CARDS

CompactFlash
Although by no means as popular as they used to be, CompactFlash cards are far from extinct and manufacturers are still launching digital cameras and handheld computers with the slots to use them.

These cards are on the chunky side but they're also remarkably robust and resist a surprising amount of abuse. They're also extremely cheap - a 512MB card costs just £86. CompactFlash cards used to be available with capacities of 4MB and up; now you'll be hard-pressed to find a new card under 64MB.

To complicate matters, there are actually two types of CompactFlash card. Type I cards are the most common and that includes all CompactFlash memory cards. Type II cards are almost twice as thick and require a bigger Type II slot, although these slots can still use Type I cards. Type II cards aren't memory cards, though, they're usually miniature hard disks, modems and network adaptors.

Price from: £15 (64MB)
Capacity: Up to 512MB
Used in: Digital cameras, handheld computers

SmartMedia
When CompactFlash was King, SmartMedia was the young pretender but this format only managed to find its way into digital cameras and little else.

SmartMedia cards are large, flat and flexible and that means that they need to be handled with care, since they can be easily bent and cracked. They are marginally more expensive than CompactFlash and have a 128MB capacity limit.

Unlike CompactFlash cards, SmartMedia cards are also 'dumb' - they lack an onboard 'controller' that tells devices how to use them. As a result, older devices may have trouble using higher capacity cards, since their software can only handle the small capacity cards that were available when they were first manufactured.

Price from: £20 (64MB)
Capacity: Up to 128MB
Used in: Digital cameras

Multi-Media Card (MMC)
The postage stamp-sized Multi-Media Card is a versatile memory card, usable in everything from digital cameras to mobile phones. The cards are cheap and tough, and while their small size makes them easy to mislay, they do have an onboard controller, which means any device can use any capacity card. It's worth noting the while MMC stands for 'Multi Media Card', it's still fine to say 'MMC card' ...

Price from: £21 (64MB)
Capacity: Up to 128MB
Used in: Digital cameras, digital music players

SecureDigital (SD) Card
Muti-Media cards are still widely available but it won't be long before they are rendered extinct and replaced by cheaper, but still compatible, SecureDigital Cards.

SD Cards have built-in copyright protection, making them much more popular with manufacturers of MP3 players and they have a write-protect switch to spare your documents from being unwittingly wiped out.

The best bit, though, is that SD Cards can be used for more than just memory. If a device has an SDIO Card slot, it can make use of cards that provide a range of other features, such as Bluetooth and Wi-Fi connections.

Price from: £25 (64MB)
Capacity: Up to 512MB
Used in: Digital cameras, digital music players

xD Card
SD Cards are small but xD Cards are even smaller. About the size of a thumbnail, xD Cards are starting to appear in some digital cameras and smartphones, and depending on who you believe, will soon be available in capacities up to 1GB.

At the moment though, xD Cards are more expensive than SD Cards and like SmartMedia cards, have no onboard controller. Whether or not this means current xD Card-compatible devices will have problems using larger cards remains to be seen.

Price from: £17 (32MB)
Capacity: Up to 256MB
Used in: Some digital cameras, Orange SPV smartphone

MemoryStick & MemoryStick MG
Not content with existing and perfectly satisfactory memory cards, Sony decided to launch its own and the result was the MemoryStick. MemorySticks look like a small stick of chewing gum but they're tough and have a write-protect switch to protect their contents.

They're priced similarly to other formats too, although ordinary MemorySticks max out at 128MB. Unfortunately MemoryStick is a proprietary format and while slots are common on all manner of Sony devices, from Clie handheld computers to Aibo robot dogs, you're unlikely to see one anywhere else.

Worse still, there's a 'secure' variant of MemoryStick called MemoryStick MG (short for MagicGate). These are used on Sony's digital music players, where they can safeguard copyrighted music.

Unfortunately, while a MemoryStick MG will work in an ordinary MemoryStick slot, the oppositeisn't true and MemoryStick MGs are more expensive.

Price from: MemoryStick £25 (64MB); MemoryStick MG £35 (64MB)
Capacity: Up to 256MB
Used in: All Sony products that use memory cards

MemoryStick Pro
Alas, two types of MemoryStick aren't enough for Sony. MemoryStick Pro is yet another format, this time combining the copyright protection features of MG sticks with data transfer speeds matching those of hard disks.

The cards can only be used in MemoryStick Pro-compatible slots and we have yet to see a device that has one. Some MemoryStick devices can be upgraded to use the format but they won't benefit from its greater speed.

Price from: £85 (256MB)
Capacity: Up to 1GB (£529)
Used in: Very little at the moment ...

MemoryStick Duo
Did we say three types of MemoryStick? Sorry, we meant four but it's unlikely that Sony will stop at MemoryStick Duo. Essentially a small MemoryStick for use in small devices, MemoryStick Duois pricey and has a limited capacity.

It has limited application too and at the moment, the Sony Ericsson P800 smartphone and Sony NW-MS70 Network Walkman are the only devices that use it. The card is supplied with a normal MemoryStick adaptor though, so it can be used in ordinary MemoryStick slots.

Price from: £41 (64MB)
Capacity: 64MB
Used in: Sony Ericsson P800 and Sony NW-MS70

Refresh my memory
Memory cards are a type of solid state storage - storage that relies on electronics rather than moving parts to hold informationg. Technically, computer memory is solid state storage too but since that loses its contents when a computer is switched off and memory cards don't, there must be a difference.

That difference is that memory cards are a type of solid state storage known as EEPROM. Electrically Erasable Programmable Read-Only Memory simply means memory that can be read and written to using an electric current and that keeps its contents even when it doesn't have power.

If you want to be even more pedantic, memory cards aren't just EEPROM cards, they're actually a subset of EEPROM called 'flash memory' but this distinction is really only of value to people who write information like this. Stick to calling those bits of plastic 'memory cards' and evenpeople in lab coats will know what you mean.

Slot machines
Nine different memory card formats does not make for an easy time when it comes to getting information off a card and onto a computer. All memory card-based devices can be plugged into a PC with a USB lead but this approach can soon lead to a lot of mess.

The solution lies in a memory card reader. This is simply a box of slots - the box plugs into a USB port (or is sometimes fitted into a free drive bay), which means you can plug in a memory card and treat it just like another disk drive.

The more slots a memory card reader has, the more versatile it is. The most versatile model we've seen is the Mitsumi 7-in-1 USB Media Drive. This has slots for every type of memory card except xD but to make up for that, it has a built-in floppy disk drive too.

Available from: www.dabs.com

Contacts:

Active Prices
www.computeractive.co.uk/activeprices

Crucial Technology 0800 013 0330
www.crucial.com/uk

Dabs.com
www.dabs.com