DOCUMENT ID:  1258-02

SYNOPSIS:     How does fdisk obtain physical geometry parameters

OS RELEASE:   2.1, 2.4

PRODUCT:      Solaris

KEYWORDS:     fdisk physical geometry parameters disk drive


DESCRIPTION:

Describes the procedures used by fdisk to obtain the geometry parameters
display when using the "fdisk -G" command. 


SOLUTION:

Two types of disk drives technologies are most common: wd1003 and SCSI. 
The wd1003 types include IDE, MFM, RLL, and ESDI.  These drives usually
use CMOS entries to announce availability to the system.  The wd1003
terminology is a result of its being the first controller used by IBM in
the AT series. 

SCSI disks don't have any indication in CMOS.  The controller BIOS will
announce availability to the system.  Some controllers will emulate
geometry's for DOS compatibility.  SCSI technology specifies disk drives
to have physical parameters written on them as part of the manufacturing
process. 

Fdisk issues an ioctl command to the disk driver using DKIOCG_PHYGEOM
parameter.  The geometry of the disk indicated by the ioctl reference
will be returned.  Two different sources are used to obtain actual
parameters: wd1003 (CMOS) and SCSI (the actual disk drive).  SCSI has a
command "Get size" to ask the drive for parameters.  SCSI controller
emulation may return other than actual parameters. 


DATE APPROVED: 02/15/95