When you want to store something permanently on a PC, the chances are that it's a disk (or disc) that comes to the rescue. Whether it's hard or floppy, compact or Zip, disks offer the cheapest and simplest way of storing anything from a couple of documents to a couple of million images. The problem with disks and the drives needed to use them, however, is their size.

When it comes to handheld computers, digital cameras and MP3 players, disk-based storage is simply a non-starter (although Iomega's PocketZip is an exception to this rule). What's needed is something smaller, less power-hungry and, considering that portable devices tend to get chucked about, sturdier. Cue the memory card.

Memory cards are made from similar material to the Ram (Random Access Memory) memory used in PCs - hence the name 'memory' card. Since they have no moving parts, they're also sometimes referred to as 'solid-state' storage but providing you don't confuse what they do with the function of Ram memory, calling them memory cards is just fine.

Unfortunately, confusion does play its part with memory cards and it's all down to the sheer number of different types available. You can choose from SmartMedia, CompactFlash, Memory Stick and more. How do you decide which one is right for now and the future? Read our complete guide to card formats to find out and then thank us for the memories.

Cards on the table

Although memory cards work in a 'similar' way to computer memory, it's not the 'same' way. Computer memory (or Ram) only keeps its contents when the PC is switched on - switch it off and everything in it is lost (which is why PCs have hard disks). Once something is stored in a memory card, on the other hand, it stays there until it's deleted.

Techno fans will happily bark on about the differences in power requirements and data transfer speeds of the various memory card formats but take it from us - unless you've a nanosecond hand on your watch you won't be worrying about them. Portable memory cards transfer data in moments and require less energy than a Sunday morning lie-in.

Abbreviated history

If you adore tongue-twisting abbreviations then you'll love the Personal Computer Memory Card International Association, or PCMCIA for short. It was set up in 1989 with the aim of drawing up standards for memory cards.

Dozens of companies collaborated to produce the first specification, appropriately labelled the 'Type I PCMCIA card' (or just 'PC Card'). By today's measure, the first memory cards based on this standard stored very small amounts of data - typically a few kilobytes - though later versions marched through the megabyte mark.

As a portable memory card format, the main problem of Type I PC Card memory is its size. While its credit card dimensions are fine for slotting into notebook computers, they're still too big for small gizmos like handheld computers and MP3 players. These days, Type I PC Card memory is about as popular as root canal surgery and manufacturers instead concentrate production on Type II PC Cards - the PCMCIA's second standard.

The Type II specification allows for marginally thicker devices than Type I (5mm compared to 3.5mm) but both types of card can still be used interchangeably in the same slot. The improvement gave PC Card manufacturers the extra room needed to make more than just memory cards and the variety of Type II devices now available is fantastic - everything from modems to TV tuner cards.

Type II PC Card memory is a good option for notebook users wanting some quick and simple extra storage because PC Cards literally slot in and go but it sure ain't cheap. Leading manufacturer Kingston Technology's Type II PC Card memory, in capacities from 8Mb to 512Mb, costs from £35 to almost £1000. Still, at least you'll be left with plenty of carrying room in your pockets.

In the mid-1990s, an even bulkier PC Card specification was introduced - Type III. This third incarnation measures 10.5mm thick and is proving popular for miniaturised hard disk drives (see the panel headed 'Disk data'). These aren't solid state but they offer more storage space than memory cards and at a lower cost.

Smart move

If you were following the above trend then you might believe the PCMCIA is obsessed with making things bigger with each revision. In fact, the organisation also operates at the opposite end of the size scale, setting out the guidelines for the slimmest memory card format - SmartMedia. When we say slim we really mean it: SmartMedia cards are less than a millimetre thick. They're not much bigger in the other two dimensions either - about the size of a postage stamp.

SmartMedia cards are a little too lightweight though: they're as fiddly as tiddly-winks, while the flimsy frame begets kid-glove handling. Also, the exposed metal contact is prone to scuffs and scratches, potentially rendering a card unusable. For this reason, once fitted, SmartMedia cards are best left in place.

SmartMedia cards also seem to cost a little more than their contemporaries, at least at the 64Mb level. A quick online price comparison at press time showed them floating around the £90 to £100 mark, while CompactFlash cards - the chief alternative - sell for £10 to £20 less. However, the memory market is a volatile one, so check current prices close to when you want to buy.

The top sheet on the PCMCIA's blueprint easel is the Miniature Card, which the Association boldly describes as the "newly adopted memory card standard". Trouble is, that sheet's been sitting there for a good few years now, so miniature cards are probably best avoided.

A little flash

Next to SmartMedia, the CompactFlash format is probably the closest the industry can offer to a true standard at the moment. About the size of a small matchbook, CompactFlash cards have an insubstantial but sturdy feel about them. As well as supplying the storage for many a digital camera and audio player, Microsoft has branded the format as the 'industry standard' for its Pocket PC specification - and if Microsoft says it's a standard, it's a standard.

Price-wise, CompactFlash is a little cheaper than SmartMedia. The format has a couple of other advantages over the competition, not least of which is capacity: the latest models can store an impressive 256Mb of data.

Looking ahead, the CompactFlash Association has come up with CompactFlash II - much the same only slightly fatter.

Like the Type I/II/III PC Card standard, this will enable manufacturers to build more complex CompactFlash cards while retaining compatibility with older devices. Modems have appeared in the form of CompactFlash II cards.

Multi story

"The MultiMediaCard Association was founded in 1998 to promote the adoption of the MultiMediaCard (MMC) as the global, open standard for removable, solid-state memory. The organisation's 80+ members represent all branches of mobile electronic applications in supporting this convenient, reliable, rugged and lightweight memory standard."

Sounds rather grand, doesn't it? Well, actually the MMC Association is little more than the outwardly independent face of just two companies - SanDisk and Infineon Technologies. Don't get us wrong: MultiMedia Cards are just as fine as any other memory card format but it's no more a 'global, open standard' than any other here.

The bottom line is that right now, MMC is the smallest memory card format in the world - and also an overpriced player on an overcrowded field. Available in 32Mb and 64Mb formats, you should expect plenty more hype from the MMCA over the next few months.

It's a stick-up

Sony is a big company. Sony makes a lot of very attractive products. Sony also makes the Memory Stick. It would be unfair to criticise any one company for coming up with yet another 'standard' but Sony's arrogance takes some beating.

The company promotes the Memory Stick as though it were the first and only memory card in existence, as well as outlining many supposed advantages of adopting the format. However, all but one of the 'advantages' - a write-protect switch to protect data - are shared by most of the other options here.

Sony is determined to make the Memory Stick the memory card standard and it could well pull it off. If you want to buy Sony products in the future, then you'll be buying into the Memory Stick concept, whether you like it or not.

A small thumbs-up

Here's an interesting alternative: a memory card that plugs straight into a USB port. That's all the installation the ThumbDrive needs, after which it can be treated just like another disk drive. The advantage is that it can be plugged in and used on both notebook and desktop PCs.

The disadvantage is that very few pocket gadgets feature USB ports, so the ThumbDrive is useless to most handheld computer owners. It also costs a small fortune - £659 for the top-of-the-range 512Mb model.

Up to standard

So, there you have it. All the major memory card standards explained. Isn't it great to have so much choice? Well, no - it's a pain in the purchase process. We understand that every manufacturer has a desire to promote its own technologies and preferences but there's little advantage from the consumer's point of view.

Economies of scale have brought down the cost of other storage media, like PC Ram memory modules, floppy and hard disks, but right now the removable memory card market has too many formats fighting for too few customers.

What's more, the situation carries the interesting side-effect of reducing consumer choice: you might crave the chic of Sony's Memory Stick Walkman but be put off because the memory card format differs from that of your digital camera and pocket computer.

To be blunt, a good shakeout is needed. Creating proprietary standards might seem like a beezer wheeze to a company like Sony but it's about as beneficial to consumers as a pebble shop at the seaside.

Given that all the cards do essentially the same thing - store digital information - in the ideal world, there would be only one format. As it stands, and given the choice, we'd strongly steer you towards the two most popular formats of the moment - CompactFlash and SmartMedia.

Disk data

The two most off-putting aspects of memory cards are cost and capacity. If you need to store more than a few megabytes, then you can expect to pay through the nose and that's assuming you can find a capacious enough card in the first place. One alternative is to consider a portable hard disk instead.

Kingston Technology produces the Datapak, a 1Gb hard disk on a Type III PC Card selling for around £350 - much cheaper than the same capacity bought in memory cards. Better still is IBM's tiny Microdrive, which offers 1Gb of storage on a CompactFlash II card, meaning it can be used in the new wave of palmtop and portable computers. The £400 gadget can also slot in to a PC Card adapter so it can just as easily be used in a notebook computer.

Desktop adapters

One of the advantages of removable memory cards is they allow you to swap and share data with other devices quickly and simply. This extends to desk-bound computers, too. With a memory card reader hooked up to a desktop PC, it's possible to zip data back and forth just like using floppy disks, which is especially useful if you have several data-containing cards to process.

There are readers for virtually every type of memory card, though perhaps the most useful is a combination unit able to swallow both CompactFlash and SmartMedia. Online shop Dabs.com has a £49 model that connects via USB, speeding data transfer. Notebook users can also benefit from card readers.

PC Card-based adapters cost around £10 and allow notebook owners to use SmartMedia or CompactFlash memory cards, rather than bulkier (and costlier) Type II flash memory.

Kingston 01932 738888 www.kingston.com

Simple Technology 01355 572850 www.simpletech.com

Psion 0870 608 0680 www.psion.com

Dabs 0870 429 3120 www.dabs.com

Sandisk 01923 671222 www.sandisk.com

IBM 0990 426 426 www.ibm.com/uk

Personal Computer Memory Card International Association www.pc-card.com

CompactFlash Association www.compactflash.org

MultiMediaCard Association www.mmca.org

Sony Memory Stick www.memorystick.org

DataMind (ThumbDrive) 0800 970 1416 www.thumbdrive.org.uk.

Jargon buster

Hard disk A high-capacity, non-removable disk drive used in almost all PCs to store applications and documents. Hard disks are so-called because they use rigid magnetic disks to store data. Hard disk storage capacity is measured in gigabytes.

Kilobyte A measurement of capacity of a storage device. Equal to 1024 bytes.

Megabyte A measurement of storage capacity - usually for computer memory. 1Mb is equal to 1024Kb (kilobytes).

PC Card A credit card sized device for adding anything from a modem to a memory card to a notebook PC. Requires a PC Card slot (standard on all notebooks).