Messages in this thread | | | Date | Mon, 3 May 1999 13:45:49 +0100 | From | Roger Gammans <> | Subject | Re: disk geometry change |
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In article <199904251319.PAA26535@wsdw01.win.tue.nl>, Guest section DW <dwguest@win.tue.nl> writes > From dledford@redhat.com Sun Apr 25 05:04:21 1999 > > Guest section DW wrote:
> > It is a myth that it is possible to derive the geometry used > > from the partition table. These days there seems to be a > > fairly standard convention that partitions should end on a > > cylinder boundary, but many fdisk versions will allow the > > user to select arbitrary partition boundaries. Not only Linux > > fdisk, but for example also certain Windows NT versions for > > the Alpha do this. > > [snip] > > ... But, more directly to your complaint, it's easy > enough to tell when the partition sizes you deduce from the disk don't > match the capacity (or even come close) and fail on the partition based > geometry detection. If you get fairly close, then you know you did the > right thing. There's no myth about it except in your mind. > >Ah, Doug - you are angry and start writing nonsense. >0. LILO and fdisk want to know H (the number of heads) and S (the number >of sectors per track) and the total disk capacity. >1. Now you come and look at a partition table. >In the great majority of the cases you can read off H and S from >the ending (c,h,s) of the first nonempty partition, since you will >usually have H=h+1 and S=s. There is no way to derive the number >of cylinders or the total capacity from the partition table.
Agreed. But there is a better way of deriving the H & S parameters, since the Absolute Start and length of the partion are stored it is possible use the soln 2 simultaneous eqns to get H & S.
I already a tool for I use in DOS which does exactly that.
>Since BIOSes usually do not tell you what the number of cylinders is >because they are afraid of mentioning numbers above 1024, the only >sensible thing is to set C = capacity/(H*S). >There is nothing to compare to see whether you did right. >It is fairly common to have partition tables that do not cover >the entire disk. >(And all this is assuming a DOS-style partition table, but people >also use other kinds of partition tables, look at genhd.c and see >what variation Linux supports today; trying to look at sector 0 >will certainly fail for such other partition table types.) Indeed.
TTFN -- Roger Gammans
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