Understanding SD Cards

I don't get why they capped the speed on SDHC, unless the speeds of standard SD are BS. :nenau
 
I imagine it's something to do with the guaranteed throughput on the HC standard. The older ones might be able to burst to something higher but not sustain it. You need a guaranteed throughput for video which is where these are mostly targetted.

The SD part of the name denotes the fact the cards are encrypted. Likely the speed of the logic doing the encryption plays a big part in whether it can sustain a particular rate of write traffic too.

Also, be really careful when looking at the letter 'b' in specs. B=Bytes, b=bits. so your 22mb/s is 22/8 (best case, not allowing for encoding/parity/ecc) =2.75 MB/s.

Get a kosher card and you'll know it adheres to the spec. I got a £30 4GB Sandisk UII in an airport earlier in the year, with a usb reader. Not dropped a single bit so far. The pirate ones are just waiting to drop your data on the floor as soon as you think you'll need it.

Bit more detail on here... http://en.wikipedia.org/wiki/Secure_Digital_card
 
ianf said:
The SD part of the name denotes the fact the cards are encrypted. Likely the speed of the logic doing the encryption plays a big part in whether it can sustain a particular rate of write traffic too.
Click to expand...

I think the data can be encrypted, but only for DRM purposes and it's not under user control. This feature arose because of the manufacturers' fears about people copying and storing music.

I have a load of SD cards that I use in multiple devices and they never fail to read - if there was any encryption going on whatsoever, you would need passphrases or digital certificates to enable access.

Mind-you, if they have to include the crypto-speed in the throughput tests, the good news is that access to the card will be a lot faster when it isn't being used :thumb2
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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