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CompTIA A+ Certification All-in-One Exam Guide

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are critical for figuring out whether a card can keep up with a device like a

video camera. But these days, SD cards are just as likely to be used in a

smartphone as they are in a camera. That’s where the Application

Performance Class ratings come in. This standard has two classes, A1 and

A2. They both support a minimum of 10 MB/s sustained write. Where they

differ is how many input/output operations per second (IOPS) the card can

do. The A1 class can sustain 1500 IOPS while reading and 500 IOPS while

writing. The A2 class can keep up with at least 4000 IOPS while reading and

2000 IOPS while writing. These performance characteristics don’t matter

much when a card is writing video, but they make all the difference when

multiple smartphone apps are using it.

Beyond these ratings, SD cards often have a maximum read-speed (in

MB/s) printed on the card or packaging. This practice started years ago with

cards oriented toward professionals, but has become relatively common on

cards of any quality. If you’re wondering why the maximum write speed isn’t

also on the card, that’s a great question; while it isn’t printed on any card

we’ve seen yet, product listings for high-performance SD cards typically

mention the maximum write speed.

Because there’s a wide variety of SD cards available with different

qualities, two cards of the same capacity can vary wildly in price and

performance. It’s important to evaluate each card’s properties to avoid

wasting money on performance you don’t need, or thinking you got a great

deal on a massive card only to find it can’t keep up with your brand-new

professional video camera.

xD-Picture Card The proprietary Extreme Digital (xD) Picture Cards (see

Figure 10-50) were about half the size of an SD card. They were used in

Olympus and Fujifilm digital cameras. The xD-Picture Cards came in three

flavors: original, Standard (Type M), and Hi-Speed (Type H). Fuji and

Olympus have moved on to using SD cards in their cameras; you’ll see xD

cards only on the CompTIA A+ exams.

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