SD Card read on De2-70

Hi all,

I'm doing a project which requires to read file from SD Card and I have some troubles

I write a txt file which contains "Hello world ! 1 2 3" to SD Card, then I use HxD to check its address. And here is the captured picture

https://www.alteraforum.com/forum/attachment.php?attachmentid=8375

I don't know what the Offset is. And what the exact address that can help me to access the "H" character in "Hello world ! 1 2 3" ?

Could you please help me ?