There are different types of memory cards available for digital cameras.

It's not just the amount of photos they can store but there are varying sizes and types.

Here are the most commonly used in digital cameras:

SD / MMC (Secure Digital / MultiMedia Card)
This is the most popular format and certainly the lowest priced. Canon uses this type.

XD
This is the type used in Olympus and FujiFilm digital cameras. It is a more expensive card, nearly twice as much as SD.

Memory Stick
This is type used in Sony digital cameras. Although more expensive than SD, it is quite versatile if you have other Sony products ranging from mobile phones to video cameras.

Different Capacities and Speeds
Below is a table which gives a guide to how many photos you can store on different size cards and different megapixel cameras.

The next table shows how fast your card will be at storing photos on the camera and copying to your computer. Faster speeds are benefical for higher megapixel cameras and taking photos one after the other quickly.

Approximate Storage Capacity
Megapixel	64MB	128MB	256MB	512MB	1GB	2GB	4GB	20GB	40GB
2MP	74	148	296	592	1184	2368	4736	9472	18944
3MP	54	108	216	432	864	1728	3456	6912	13824
4MP	33	66	132	264	528	1056	2112	4224	8448
5MP	25	50	100	200	400	800	1600	3200	6400
6MP	21	42	84	168	336	672	1344	2688	5376
7MP	19	38	76	152	304	608	1216	2432	4864
8MP	16	32	64	128	256	512	1024	2048	4096
Transfer Speed Rates
Card Speed	Data Transfer Rate
8x	1.2 MB/sec
12x	1.8 MB/sec
20x	3.0 MB/sec
25x	3.8 MB/sec
30x	4.5 MB/sec
40x	6.0 MB/sec
60x	9.0 MB/sec
66x	10.0 MB/sec
80x	12.0 MB/sec
100x	15.0 MB/sec
120x	18.0 MB/sec
1X Speed is 150 kilobytes (KB) per second