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Old Jul 12, 2005, 7:04 PM   #1
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Hi Folks

I just bought a new camera for my wife (Canon A510). I also bought an upgraded memory card to go with it, a SanDisk 512MB. The camera indicates the card has 483MB of storage with 32KB already in use.

Now, even if you add 483MB and 32KB, it doesn't come near 512MB. I went back to the store and the guy said that was normal, but he couldn't really explain why.

Is this normal? If so, where does the manufacturer get "512MB" from, out of thin air perhaps? :roll:

Thanks!
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Old Jul 12, 2005, 7:17 PM   #2
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It's essentially a trick, but they're legally covered and everyone in the indsutry does it.
Essentially it boils down to:
As far as the manufacturers are concerned, a Mega Byte is made up of 1,000,000 bytes, but as far as the computers are concerned (and a camera is effectively a type of comptuer) a Mega Byte is 1,048,556 bytes, so when you get the card in your camera you get less MB than you expect.
Do the maths and you'll see this adds up to 506MB being accounted for (if I did it right ), with the other 6MB missing because of the way the camera formats the card.
As I said, this happens with everthing - check your hard drive on the PC and you'll see the same thing has occured.
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Old Jul 12, 2005, 8:41 PM   #3
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Thanks for the reply. I hear what you're saying, although I can't get the sums to work out. I guess it's like calculating mortgage interest; I could never understand how the bank does it!! :?
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Old Jul 13, 2005, 9:35 AM   #4
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superstring wrote:
Quote:
Thanks for the reply. I hear what you're saying, although I can't get the sums to work out. I guess it's like calculating mortgage interest; I could never understand how the bank does it!! :?
In addtion to the way memory card manufacturers calculate space (as MrPogo explained), a small portion of the space on the card is also used for the File Allocation Table; and with Secure Digital, some of it used for the Security Features built into the card (which no camera manufacturer takes advantage of yet). This security area is not visible to the operating system.
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Old Jul 13, 2005, 12:49 PM   #5
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Thanks again, guys. I guess the guy at the camera store wasn't trying to dupe me after all! :G
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