Re: GPT - (last) call for action

Hi, all--

On Jun 10, 2007, at 3:13 PM, Rui Paulo wrote:
>> :Media sector size is 512
>> :Warning: BIOS sector numbering starts with sector 1
>> :Information from DOS bootblock is:
>> :The data for partition 1 is:
>> :sysid 238 (0xee),(EFI GPT)
>> :    start 40, size 409600 (200 Meg), flag 0
>> :        beg: cyl 0/ head 0/ sector 41;
>> :        end: cyl 406/ head 6/ sector 14
>>
>>     I think I have it mostly figured out, but the 'start 40' in your
>>     output can't be right.  The intel documentation says that the
>>     starting LBA in a PMBR record must be set to 1 by definition
>>     (table 11-7 in the 1.10 documentation).
>
> I don't know why Apple does that.

The offset of 40 sectors sounds like it is pointing to the first  
partition listed within the GPT?

A typical Intel Mac system using GPT ought to look something like this:

# fdisk /dev/rdisk0
Disk: /dev/rdisk0       geometry: 9964/255/63 [160086528 sectors]
Signature: 0xAA55
          Starting       Ending
#: id  cyl  hd sec -  cyl  hd sec [     start -       size]
------------------------------------------------------------------------
1: EE 1023 254  63 - 1023 254  63 [         1 -  160086520] <Unknown ID>
2: 00    0   0   0 -    0   0   0 [         0 -          0] unused
3: 00    0   0   0 -    0   0   0 [         0 -          0] unused
4: 00    0   0   0 -    0   0   0 [         0 -          0] unused

# 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
   159824344     262151
   160086495         32         Sec GPT table
   160086527          1         Sec GPT header

The first, small partition is almost certainly a "boothfs" boot  
partition, as described in the man page for Apple's version of fdisk:

"     In the default template, partition number 1 will be configured  
as a Dar-
      win boot partition spanning from cylinder 0, head 1, sector 1, and
      extending for 8 megabytes.  Partition number 2 will be  
configured as a
      Darwin HFS partition spanning the rest of the disk.  This mode is
      designed to initialize an MBR the very first time, or when it  
has been
      corrupted beyond repair.

      You can specify other default partition styles with the -a  
flag.  The
      available styles are:

      boothfs     Creates an 8Mb boot partition (type AB hex) and  
makes the
                  rest of the disk a Darwin HFS partition (type AF hex).

      bootufs     Creates an 8Mb boot partition (type AB hex) and  
makes the
                  rest of the disk a Darwin UFS partition (type A8 hex).

      hfs         Makes the entire disk one Darwin UFS partition  
(type A8 hex).

      ufs         Makes the entire disk one HFS+ partition (type AF  
hex).

      dos         Makes the entire disk one DOS partition (type 0C hex).

      raid        Makes the entire disk one type AC hex partition.

      The -u flag is used to update the MBR code on a given drive.   
The MBR
      code extends from offset 0x000 to the start of the partition  
table at
      offset 0x1BE.  It is similar to the -i flag, except the  
existing parti-
      tion table is preserved. This is useful for writing new MBR  
code onto an
      existing drive, and is equivalent to the DOS command ``FDISK / 
MBR''.
      Note that this option will overwrite the NT disk signature, if  
present.
      The -u and -i flags may not be specified together."

Also cf: http://en.wikipedia.org/wiki/GUID_Partition_Table

-- 
-Chuck