Ever wondered what X-speed is or what the difference is between a flash card that has a write speed of 20M bps versus one that has a read speed of 23M bps?

Simply put, X-speed is a rating system that provides users with a performance indicator of how fast a flash card can transfer data. The higher the X-speed rating the faster the flash card performs.

According to Caroline Macharia, Axiz flash memory product manager: "The time it takes to write data to a flash card when using it in a digital camera or cell phone has become an important buying criterion for consumers."

Macharia says that when consumers are shopping around for flash cards and compare the X-speed ratings from different manufacturers, they need to be aware of the different ways in which the X-speed rating is defined.

It is often referred to as the "read" or "write" speed or "data transfer" speed referring to both the read and write speed. Certain manufacturers communicate the X-speed of the flash card as the write speed, because they are more concerned about the time duration of writing data to a flash card, especially when using host devices, such as digital cameras or cell phones.

Read speeds are typically higher than write speeds for flash cards but the write speed tends to be a more meaningful indicator when measuring the flash cards" performance.

But is the faster "X" speed rating better? "Not necessarily," says Macharia. "Host devices such as cell phones or digital cameras are limited by the speed of their interface to the flash card as they tend to have a lower read and write speed.

This results in a high performing flash card that cannot perform at its" optimum as it is hindered by the host devices read and write speed."

To purchase the correct flash card the first time round, consumers need to be aware of how X-speed ratings on flash cards are communicated. As a rule of thumb the higher the X-speed rating the faster the data is transferred, and the shorter the duration of downloading data from the flash card.