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Old Apr 4, 2009, 7:00 PM   #31
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DonalDuc wrote:
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Show me ONE ... ONLY ONE! .... SD card with Class2 or Class4 or Class6 ...
http://www.sandisk.com/Products/Item..._Card_2GB.aspx

http://www.sandisk.com/Products/Item...II_SD_2GB.aspx

http://www.sandisk.com/Products/Item...II_SD_2GB.aspx

http://www3.pny.com/2GB-Optima-Secur...-P2340C40.aspx
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Old Apr 4, 2009, 8:16 PM   #32
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Sorry, especially SANDISK fools consumers - they have a lot of SDHC WITHOUT class-declaration and some "SD" with fantasy-class-declaration.

I don't know another manufacturers who makes such sh.i.t.

They also have "videoHD"-SDHCs to give the impression, other cards are not suited for hd video. class4 is to slow for hd video - f.e. Canon SX1 ... 43 Mbps = 5.4 MBps

Otherwise the write on class 4 "15mb" - I think they don't know about SD/SDHC/CLASS. But their prices are 3x as high as other cards!

Is a Sandisk class4 15 mb card a class 4 or is it a class15 ? Or vary production so, that class 4 is garanteed and they fool people with "on sunny day and withfresh oiled camera you can perhaps .. and with luck ... reach15 mb" ?

I also saw Sandisk cards, written "microSD" - but they were microSDHC! -There exist NO 4gb microSD! (but non-standard 4gb SDs)

Fine, fine ... malfunction in non-SDHC phones, GPS or cameras :-(

Sandisk is NO reference for SD or SDHC !












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Old Apr 4, 2009, 8:22 PM   #33
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http://www3.pny.com/2GB-Optima-Secur...-P2340C40.aspx
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Old Apr 4, 2009, 8:26 PM   #34
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DonalDuc wrote:
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Is a Sandisk class4 15 mb card a class 4 or is it a class15 ?
One more time, the Class is for the MINIMUM transfer rate. The 15MB/s spec (not "15 mb")on the card is the advertised MAXIMUM transfer rate.
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Old Apr 4, 2009, 10:36 PM   #35
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Wow! I know the difference 15mb/s - 15mb Mr. GrammarTeacher!

class4 = 4mb

15mb = 15mb ... ööööhhmmm mb/s ... this is .. where's my solar calculator ... 375%

hmmmm, if card is in good good mood, it makes 15 ... in bad mood only 4 mb ... ööööhmmm ... mb/s ?

Sandisk knows this? Else tell them !!! Reward ... I'm sure you get one 2gb SD-card, class5 for half price!


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Old Apr 5, 2009, 8:18 PM   #36
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Manufacturers advertise the speed of their flash memory cards using the most flattering method possible. That method is to measure the sustained throughput of the media itself. That's the 15MB/s on the SD Card in your image, or the more common 'X' rating, which is the samerating CD drives use, where 15MB/s is 100X.

The way that the operating system uses flash memory is very different. When the operating system has data to write to a flash memory card, it checks the File Allocation Table (FAT) for the location of an empty cluster. Then it writes the data until it is either complete or until the cluster is full. (This process could actually take place at the speed stated by the manufacturer.) Anything that is written to flash memory is automatically verified, so the cluster that just got written to is read from to see if the data that was just read matches what was just written. If it doesn't match, the cluster, sector or byte is marked as bad, and the data is written and verified again. Once the write is verified, the cluster is marked in the FAT as containing valid data.

Except for the actual writing of the data, the entire process can take quite a while, and must be completed before another cluster of data can be written. And only a very small part of it happens at the speed marked on the card. The SD Speed Classes are certifications that all that stuff will happen at least as fast asthe speed specified by the class. That's why the maximum speed of the card and the Class of the card are very different.
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