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What the ‘x’ Means When it Comes to Memory Card Speed


Instead of labeling their memory cards in MB/s, some manufacturers choose to use “Times” ratings (e.g. 8x, 12x, 20x, etc…). While it’s pretty clear that a higher number indicates faster speed, what exactly is the number a multiple of?

The answer is that the memory cards are using the same transfer speed rating as the CD-ROM industry, with 1x being equivalent to the data transfer rate of an audio CD, which is 0.15 MB/sec or 1.2288 Mbps.

If a CD-ROM is read at the same rotational speed as an audio CD, the data transfer rate is 150 KiB/s, commonly referred to as “1×”. At this data rate, the track moves along under the laser spot at about 1.2 m/s. […] By increasing the speed at which the disc is spun, data can be transferred at greater rates. For example, a CD-ROM drive that can read at 8× speed spins the disc at 1600 to 4000 rpm, giving a linear velocity of 9.6 m/s and a transfer rate of 1200 KiB/s. [#]

Even though memory cards don’t use moving parts and have nothing to do with audio CDs, some manufacturers continue to use this measurement standard for labeling their cards.

How Fast Should Your Camera’s Memory Card Be? [NYTimes]

Image credit: New SD cards for the new equipment coming by NoWin