SD block offset of 251 blocks

I found out that my Windows 7 laptop skips the first 251 blocks of an SD card. When I make a raw dump of an SD card, block 0 on my Windows 7 laptop corresponds to block 251 on my Windows Vista l开发者_如何学Pythonaptop. I believe that my Windows Vista laptop is being correct, because the block numbers correspond directly to the block numbers I use when writing using a microcontroller.

Why does Windows 7 have this offset? And is this caused by Windows, or is it something that my SD card reader does? And how can I circumvent this?

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Wild guess: The Card has a partition table, and the (one) partition starts at sector 251. Your tool reads the complete card in Vista, but accidentaly in Win7 you read the partition only.

But this is hardly programming related...