Truth Behind SD Card Speed Claimed By Different Companies

[abhi.r 95]

As recently I wanted to purchase a MicroSD card for my phone, I came thru this link. Thought I might share with you all...

Identifying the speeds of SD cards is confusing. The card to the left is marked Class 4, as indicated by the number 4 with a big ‘C’ around it. Until today, ‘Class 4′ meant nothing. It was one more element to confuse with all the other statements of speed, like Mbit/s and MBytes/s and 133x.

The table below shows the actual speed of different Classes of cards.

SDHC Speed Class Rating

Class 2: 16 Mbit/s (2 MByte/s)

Class 4: 32 Mbit/s (4 MByte/s)

Class 6: 48 Mbit/s (6 MByte/s)

Class 10: 80 Mbit/s (10 MByte/s)

Note these are straight conversions: 32 Mbit/s = 4 MByte/s

(much like measuring temperature: 32F = 0C)

Since the Canon T2i/550D records 5.5MBytes/s, a Class 6MB/s card is required, as recommended by Canon in the manual.

However, card speeds are confused by all kinds of crazy nonsense. I accidentally bought a Class 4 card for the Canon T2i/550D which incidentally, works perfectly well after a low level format by the camera. (It didn’t work at all before a low level format.) It’s a SanDisk Class 4. It says 15MB/s on it.

WTF? If it were 15MB – according to the table above – it would be Class 15. If there was a typo, ie. 15Mb/s was meant instead of 15MB/s, then it would be Class 2. No matter how you look at it, the card has 2 wildly contradictory speeds written on it.

Extensive Googling eventually spits up a plausible explanation: when it says Class 6, it means the CERTIFIED MINIMUM speed is 6MB per second. It is certified by the SD Association. Any other mention of Mb/s or MB/s or 133x on cards are manufacturer’s claims. We can practically ignore them.

So my SanDisk card pictured above is certified Class 4 – it has a certified minimum speed of 4MB/s, and an uncertified speed of 15MB/s.

Sensible course of action:

Buy based on the Class number. Treat any other speed related information as part of the brand. Refer to speed by class number.

:SOURCE:

[ni0987 179]

thanks for sharing good information.

[Musafir 0]

It is also useful to match your needs with the speed that you pay for. Most cellphone microsd cards are used for storing music, contacts etc. You don't need a superfast card for that. DSLR cameras that record HD video do need fast cards. Figure out what you need the card for and then spend accordingly.

[abhi.r 95]

Yeah true.

But people say when using higher class SD Card... apps moved from phone to SD, move files, etc.. etc... all other actions are faster than normal Class 2 SD card.

But as Musafir said.. Higher class SD card are mainly for recording HD videos in cameras.

[mgdelhi 192]

Extensive Googling eventually spits up a plausible explanation: when it says Class 6, it means the CERTIFIED MINIMUM speed is 6MB per second. It is certified by the SD Association. Any other mention of Mb/s or MB/s or 133x on cards are manufacturer’s claims. We can practically ignore them.

NO you should NOT ignore them. SD Association stopped providing class specification after class 10 ( 10mbps ) but that does not mean world stopped there.

Today SDHC and SDXC have exceeded Class 10 by many times. So practically all newer SDXC UHS1 are Class 10 but they may differ by a large margin , Very soon you will have SDXC exceeding SATA 2 read write speeds ( 3 mbps) and if you need to distiguish between a card with 1.5 mbps and 3 mbps then this class specification is not useful at all.

The 133X speed is mentioned in terms of multiples of original CD speed so 133X is 133X150 mbps

This indication is more appropriate as all kinds of Cards ( CF , TF, MMC etc) follow this.

[dr.faramroze 703]

I happened to come across this topic today, its relevant enough to hold the fact that Android phones require higher class sd hc/xc cards for higher read/write. Thank you Abhi. For providing sd specifications

Sent from my Nexus One using Tapatalk

[csmart 472]

transcend's ultra high speed cards and SSDs.

Source

What is UHS-1? Fastest type of SD cards!

For professionals, memory cards are never fast enough. Now we have new options: SDHC UHS-1 and SDXC UHS-1 memory cards.

UHS stands for Ultra High Speed. The symbol can be found exclusively on SDXC and SDHC products. UHS-I is the fastest category of card available today with a bus interface speed of up to 104 MB/s, while UHS-II is expected to reach 300 MB/s. SDXC UHS-I and SDHC UHS-I memory cards can achieve best performance when paired with a UHS-I device and are designed to allow consumers to record HD resolution videos, plus perform other simultaneous recording functions.

Compared with SDHC Class 10 cards, the next-generation SDHC UHS-1 cards provide much better data transfer performance, as shown in the following graphs:

Understanding Symbols

The SD Association has announced two new high-speed performance symbols for the fastest SDXC and SDHC devices and memory cards:

★ The UHS-I symbol (a bold capital letter I): for products with bus interface speeds up to 104 MB/s

★ The UHS Speed Class 1 symbol (a number 1 nestled inside a letter U): meaning it supports transfers of at least 10MB/s

＃ SDHC UHS-1 Cards

＃ SDXC UHS-1 Cards

To get the full potential of UHS-1 cards….

Does purchasing a SDHC/SDXC UHS-1 card mean you can immediately start enjoying the performance benefits offered by the new standard? The answer is: not necessarily. Unless your card reader supports SDHC/SDXC UHS-1 format, your ultra high speeds card will never reach its ultimate speed potential.

Let’s see the following charts. Using a 8GB SDHC UHS-1 memory card with a card reader that supports UHS-1 (right) is obviously faster than using it with the one that doesn’t (left).

If you are a laptop user, try to use your SDHC/SDXC UHS-1 card with our RDF1 ExpressCard Reader. It accepts three next-generation card formats: SDHC, SDHC UHS-1, SDXC, and SDXC UHS-1. Thanks to its lightning-fast connectivity, transferring large files like RAW digital images and high-definition videos is much easier than you think!

Edited September 22, 2011 by csmart