Very interesting. So there are SD cards which have a MBR and others that
don't have it?

How can one identify one type vs the other? Is it totally a software thing
or is there some "hardware interference" that sets to one type or the other=
?

If it's a software thing, just by rewriting the first 2 sectors (MBR) then
we can set the type as we wish.

Does a MBR-type SD card REALLY allow multiple partitions? When I did some
experiments in this regard (SD not SDHS) I think they all failed, at least
on Windows. Like if it pretended it to be a partition already, not a disc,
even if I made a custom MBR for it.

Last but not least, if I get a SD which is MBR-type (or convert one to it,
if it's even possible (hardware registers/flags?)), and make it bootable,
can I run a OS from it (through a USB-SD adapter)?

Greets,
Mario


At 02.49 2011.11.08, you wrote:
>IVP wrote:
>> Hi all
>>
>> Until recently I've been using a couple of unbranded 4GB cards that
>> format with a Boot Sector at address 0x000000, directory starting at
>> 0x761000 and first file data at 0x762000
>>
>> Now I've tried a couple of Strontium cards (half the price) and find
>> that the Boot Sector is at 0x400000, directory at 0xBAE000, first
>> file data at 0xBAF000
>>
>> 0x000000 to 0x761000 =3D 3b08 sectors, and 8 sectors to first file
>> 0x400000 to 0xBAE000 =3D 3d70 sectors, and 8 sectors to first file
>>
>> Between 0x000000 and 0x4000000 is all zeroes, except for this at
>> 0x1c0 (d448)
>>
>> 03 01 0b 2e ee e7 00 20 00 00 00 d8 7a 00 00 00
>>  =20
>Looks like your card has a "master boot record" with a partition table=20
>and then has the fat filesystem on a partition.
>
>http://en.wikipedia.org/wiki/Master_boot_record
>
>The first partition table entry starts at 0x1be and is 16 bytes long=20
>(there are places for three more entries)
>
>So your table entry is
>
>00 00 03 01 0b 2e ee e7 00 20 00 00 00 d8 7a 00
>
>decoding that according to the table at we get
>
>00: non bootable partition
>00 03 01: chs start of partition, you can ignore this and use the LBA valu=
es
>0b: parition type: "fat32 with CHS addressing"
>2e ee e7 : chs end of partition again you can ignore this
>00 20 00 00: start LBA sector of partition =3D sector 0x2000 =3D byte offs=
et=20
>0x400000
>00 d8 7a 00: length of partition  =3D 0x7ad800 sectors =3D 0xF5B00000 byte=
s
>> The directory listing of the card in XP looks perfectly normal, but how
>> does XP know where to find the Boot Sector ? I've got fatgen.doc and
>> see no special mention of location 448. 0x400000 would be the 0x400th
>> cluster (@ 512 bytes x 8)
>>
>> If 0x000000 to 0x3FFFFF is reserved, how is that communicated to
>> the PC ? I need to know so I can read any card with a dsPIC
>>
>> Alternatively, can I force the format to put the Boot Sector at 0x000000=
 ?
>>
>> TIA
>>
>> Joe
>>  =20
>
>--=20
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>http://mailman.mit.edu/mailman/listinfo/piclist

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