## formula for cylinders???

### formula for cylinders???

Help!!!  I need to find the formula for calculating the amount of
cylinders on a hard disk.  Could someone please e-mail me the formula?

-Chris

### formula for cylinders???

On 9 Apr 1996 23:31:25 GMT, Christopher B Jessen dumped the following to
comp.os.linux.setup:

Quote:>Help!!!  I need to find the formula for calculating the amount of
>cylinders on a hard disk.  Could someone please e-mail me the formula?

Uhh.. this ain't any e-mail, but there ain't any formula for your
cylinders :) ...except, of course, the fact that your hdd space in bytes
is C*H*S*512, where C,H and S are the number of cylinders, heads and
sectors respectively. so, we get number of heads by evaluating

Capasity/512*HS

;)

--
//Ed
%
But why did the chicken cross the road?
H.P. Lovecraft:
To futilely attempt escape from the dark powers which
even then pursued it, hungering after the stuff of its soul!

### formula for cylinders???

|> On 9 Apr 1996 23:31:25 GMT, Christopher B Jessen dumped the following to
|> comp.os.linux.setup:
|>
|> >Help!!!  I need to find the formula for calculating the amount of
|> >cylinders on a hard disk.  Could someone please e-mail me the formula?
|>
|> Uhh.. this ain't any e-mail, but there ain't any formula for your
|> cylinders :) ...except, of course, the fact that your hdd space in bytes
|> is C*H*S*512, where C,H and S are the number of cylinders, heads and
|> sectors respectively. so, we get number of heads by evaluating
|>
|>   Capasity/512*HS

I've got a related question.  I repartitioned a 1.7 GB micropolis drive
from a SUN to use under Linux, and fdisk reported a radically different
number of C,H, and S (842,128,32) from the numbers which were used on the
SUN (2394,15,96).  Both sets of numbers give about the same capacity
and fdisk didn't complain about the need to set these by hand from the
extra functions menu, so I went ahead and used these apparently bogus
numbers.  As far as I can tell, everything works OK, but I wonder ....
Why does this work?  Am I in for trouble later on?

In Ultrix 4.3's /usr/include/sys/devio.h, I read:

: dev_size;   /* number of blocks in the user area (#pc)*/
: ntracks;    /* number of tracks per cylinder (#nt)    */
: nsectors;   /* number of sectors per track (#ns)      */
: ncylinders; /* total number of cylinders   (#nc)      */
: attributes; /* Device attributes; see defs below      */

However, on some other operating systems like DEC OSF/1 1.3 or SunOS 4.1.3,
I see a reference to "alternative cylinders" when getting the disk geomery
info via DEVGETGEOM ioctl().  What is an "alternate cylinder" and more
importantly for me, do you include the alternate cylinders in the total
number of cylinders or not?

To be even more pratical, what if I know the recommended number of cylinders
and alternate cylinders for, say, a "Quantum PD 1050" drive from a SunOS
/etc/format.dat file which includes cylinders and alternate cylinder
numbers.  If I want to create an /etc/disktab entry for it under Ultrix, do I
use the number of cylinders or the cylinders+altcylinders number?

Thanks for any help.  Beg, plead, whimper.

--

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