:>> # gpt -r show /dev/rdisk0 :>> start size index contents :>> 0 1 PMBR :>> 1 1 Pri GPT header :>> 2 32 Pri GPT table :>> 34 6 :>> 40 409600 1 GPT part - C12A7328-F81F-11D2-BA4B- :>> xxxxxxxxxxxx :>> 409640 159414704 2 GPT part - 48465300-0000-11AA-AA11- :>> xxxxxxxxxxxx :... :> Well, what's happening is that Boot Camp syncs the BIOS partition :> table with the GPT table, so the first partition should start at 40, :> just like the GPT. :> :> Why does it start at 40 ? Because you need room for the PMBR, the :> Primary GPT header and the Primary GPT table. : :Agreed, you need about 32 sectors for the GPT header+table. It makes sense for them to point the first MBR slice at the first partition in the GPT, even though the standard says something else. It really sounds like they are making an accomodation for BIOS booting or older Windows booting... or *something* of that sort. The fact that the bootability bit is not set in the MBR (I'm not sure about that, is it set or not?)... that seems to imply a compatibility issue with other OS's like Windows in a multi-boot environment. They are just doing it all with a single slice instead of having two slices. I'll bet they found that the two-slice method doesn't work in some cases and the one-slice method does. The standard document doesn't allow either method but it does seem to be a bit less insistent on the starting sector for slice 1 then it does on there only being one slice in the MBR, period. I can also see some OS's / disk managers barfing on having two slices which overlap each other. So it really does make sense for them to point the MBR at sector 40. The more I think about it, the more sense it makes. -Matt Matthew Dillon <dillon_at_backplane.com>Received on Mon Jun 11 2007 - 18:33:48 UTC
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