Let’s fig­ure out how to choose a mem­o­ry card among the many dif­fer­ent options and what all these icons on the card itself mean.



There are two speeds that are impor­tant for any mem­o­ry card.

Read­ing speed means how quick­ly infor­ma­tion can be read from the card. For exam­ple, when you trans­fer files from a card to a com­put­er, your com­put­er “reads” the card. The faster the read­ing speed, the faster you can trans­fer pho­tos and videos to your com­put­er.

Low read­ing speed is when you put files trans­ferred from a card to a lap­top, dur­ing this time you man­age to wash, iron, do all the work, dig a gar­den, get mar­ried, raise grand­chil­dren, then return to the com­put­er, and there is only 50% of the load.

Record­ing speed means how fast infor­ma­tion can be writ­ten to the card. If you’re shoot­ing frame-by-frame, the write speed may not mat­ter much. If you often take pho­tos in burst mode, the record­ing speed is impor­tant for com­fort­able work.
Let’s take San­Disk’s card options as an exam­ple, where the Extreme Pro is a high­er-end card.

Read speed Write speed

San­Disk Extreme Pro Up to 300MB/s 90MB/s–260MB/s

San­Disk Extreme Pro Up to 170MB/s 30MB/s–90MB/s

San­Disk Extreme Up to 150MB/s 30MB/s–60MB/s

San­Disk Ultra Up to 120MB/s 10MB/s

As you can see, Extreme Pro cards have great read and write speeds. If you’re plan­ning on shoot­ing 4K video and/or tak­ing pho­tos in RAW for­mat, qual­i­ty, per­for­mance and speed are impor­tant to you, so Extreme Pro is your best bet. If you’re just get­ting start­ed with pho­tog­ra­phy, then the speed set­ting may not make a big dif­fer­ence, so to save mon­ey, you might want to opt for Ultra.

It’s impor­tant to make sure your device is com­pat­i­ble with your card’s speed. Some cam­eras require a cer­tain min­i­mum MB/s (megabits per sec­ond) to use cer­tain fea­tures. Always check the spec­i­fi­ca­tions of your cam­era before pur­chas­ing a mem­o­ry card.

Card type

- SD: These are the first SecureDig­i­tal (SD) cards with capac­i­ties up to 2 GB. You can also see them under the name SDSC;- SDHC: HC — High Capac­i­ty (High Pow­er), a new gen­er­a­tion of SD cards, increased capac­i­ty up to 32 GB; — SDXC: XC — Extra Capac­i­ty (Extra Pow­er) the third ver­sion of SD cards, sig­nif­i­cant­ly increased mem­o­ry capac­i­ty up to 2 TB or 2048 GB; — SDUC: UC — Ultra Capac­i­ty (Ultra Pow­er), the lat­est gen­er­a­tion card, announced in the sum­mer of 2018, has a max­i­mum capac­i­ty of 128 TB.

UHS bus

Bus — mem­o­ry card inter­face and com­mu­ni­ca­tion method.

Dif­fer­ences in the pinouts of the UHS‑I and UHS-II inter­faces

Dif­fer­ent SD cards have dif­fer­ent data trans­fer rates and this depends on the media type. On the map we can see the Roman numer­als I, II or III. The larg­er the num­ber, the high­er the trans­fer rate in MB/s.

- UHS‑I has a the­o­ret­i­cal bus speed of 104 MB/s, but the actu­al trans­fer rate can vary from 50 to 95 MB/s, depend­ing on your device and card man­u­fac­tur­er;

- The max­i­mum UHS-II bus speed is 312 MB/s. The actu­al trans­fer rate is about 299–300MB/s;

- UHS-III with a max­i­mum bus speed of 624 MB/s. This is the new stan­dard, most authors don’t need it.

There is a dif­fer­ence between mem­o­ry card bus speed and Speed ​​Class.

Speed ​​class

This spec­i­fi­ca­tion is rather impor­tant for video­g­ra­phers who need to know the min­i­mum con­tin­u­ous write speed for video record­ing. This is due to the tech­ni­cal details regard­ing data frag­men­ta­tion, so all we need to under­stand is what spec­i­fi­ca­tion we need.

- Speed ​​Class is the num­ber in cap­i­tal “C”, which can be 2, 4, 6 or 10. These num­bers cor­re­spond to the min­i­mum num­ber of MB/s for sequen­tial write speed. Does not require UHS‑I, II or III.

- UHS Speed ​​Class defines the min­i­mum sequen­tial write speed for ultra high speed. This is the num­ber in the let­ter “U”, which can be either 1 or 3. U1 has a sequen­tial write speed of 10MB/s and U3 has a sequen­tial write speed of 30MB/s. This requires a UHS‑I, II or III data bus. UHS Class 3 is not UHS-III.

- Video Speed ​​Class is a new speed class for high­er res­o­lu­tion video record­ing. This is the num­ber next to the “V” on the respec­tive mem­o­ry cards. The num­ber next to the V is 6, 10, 30, 60, or 90 and indi­cates the min­i­mum sequen­tial write speed in MB/s. This requires a UHS bus.

If you are using UHS mem­o­ry cards in non-UHS devices, it will default to Stan­dard Data Explor­er and use Speed ​​Class rather than UHS Speed ​​Class.

Video Speed ​​Class

Indi­cat­ed by the let­ter “V” next to the num­ber. The table below shows the range and speed of each class.

If you shoot video at 1080p or low­er, V6 or V10 is all you need. If you are shoot­ing in 4K, 8K, VR and/or drone, you will need at least V30 or high­er.


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