[clue-tech] Partition madness

[Roy J. Tellason]

On Monday 25 July 2005 11:06 am, Angelo Bertolli wrote:

> Yes, I'm an idiot.  I knew I should have just cut and pasted that.  It
> pretty much looks like what I wrote above,  except I'm not sure which
> type of Extended it is.

Extended doesn't have a type,  it's a kind of partition,  but doesn't carry a 
filesystem within it,  only on partitions inside of it.

> This is confusing to me.  Supposedly there is some kind of identifier at
> the beginning of the partition for the "type" of partition e.g. 83 for
> Linux.  That probably doesn't do anything more than provide information
> about what is "supposed" to be there ??

Nothing,  in that case.

Here's how it works:

Your master boot record (MBR) in spite of being nontrivially larger,  contains 
exactly _four_ slots (memory locations) that describe HD partitions.  You can 
use any of one to four of these.  The problem came about due to DOS having 
limits on how big a partition could be,  and other factors.  So from 
somewhere around DOS 3.3 (?) the "extended" partition was defined,  which 
just basically said "This isn't a real partition table entry,  it's a pointer 
to another table that's somewhere else on the disk."  Those can grow without 
any limit,  and contain lots of "logical drives".  That's why if you have a 
linux box with one "Primary" and other "extended" partitions the latter will 
all end up with device numbers from hda5 onwards -- hda1 through 4 will 
signify the entries in the _primary_ partition table in the MBR,  and other 
subsequent entries will signfiy entries in the extended table located 
elsewhere on the HD.

Look around for a file called "presz120.zip",  though the number part may be 
different.  This is a dos-based utility program that's supposed to allow for 
resizing partitions.  I've never actually run it,  but the doc file within it 
gives a much more detailed *excellent* explanation of all of this stuff,  
much better than what I can stuff into a message here.






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