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CompTIA A+ Certification All-in-One Exam Guide

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Figure 10-49 SD, miniSD, and microSD cards

EXAM TIP The CompTIA A+ 1001 objectives refer to miniSD and

microSD cards as Mini-SD and Micro-SD cards. Don’t get thrown off by the

naming differences.

SD cards come in three storage capacities. Standard SD cards store from 4

MB to 4 GB, Secure Digital High Capacity (SDHC) cards store 4 GB to 32

GB, and Secure Digital Extended Capacity (SDXC) cards have a storage

capacity of 32 GB to 2 TB. Early SD card readers and devices cannot read the

SDHC or SDXC cards, though the latter standards provide backward

compatibility.

When it comes to figuring out how fast a given SD card is, things start to

get complicated. Card speeds matter when it comes to intensive uses like

high-quality video and high-resolution or high-speed photography.

To try and make it easy for users to pick a card that will be fast enough for

their use, the people behind the SD cards have created a number of standards

to communicate performance. These standards roughly break down into three

different generations. The first-generation cards use the speed class (2, 4, 6,

and 10) ratings to indicate the card’s minimum MB/s write speed; a Class 10

card should write at a minimum of 10 MB/s.

The second generation of speed ratings coincided with the introduction of

the new Ultra High Speed (UHS) bus. These cards use the UHS Speed Class

standard; Class U1 cards should both read and write at a minimum of 10

MB/s, while U3 cards should read and write at a minimum of 30 MB/s.

The third generation of performance standards is the Video Speed Class.

These standards are designed to support the newest video standards such as

4k and even 8K. The slowest class is V6, supporting 6 MB/s, but it goes all

the way up to V90, which guaranties 90 MB/s write speed. If this wasn’t

confusing enough, modern cards often sport indicators for more than one (if

not all) of these speed rating systems.

But wait, there’s more! The speed classes we’ve looked at guarantee that a

card can continuously write at the indicated rate or higher. Ratings like this

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