On Thu, 2012-07-26 at 02:34 +0100, John Lane wrote: > Hello, I'm in the middle of studying disk organisation to enhance my > understanding in this area. I have a few questions about fdisk (trying > to fill a gap in my knowledge if that's ok)... use the source, Luke :) > > In the below output of fdisk it shows (correctly) a geometry of 224 > heads, 56 sectors/track. I'm unclear about where this information comes > from. Normally a disk's geometry would be reported as 255 heads and 63 > sectors. I explicitly partitioned this disk using a 224/56 geometry, so > the report is correct. I'd just like to understand: > > (a) where fdisk gets the information about the geometry from in this > specific case? fdisk gets the information from (i) user input, (ii) what the kernel/bios thinks the geometry is, with the HDIO_GETGEO ioctl and (iii) by inferring it from the partition table geometry. > (b) when fdisk defaults to 255/63 is that because it's hard coded that > way or is there another reason? Correct. > > I understand why it's 255/63 by default but haven't been able to > understand how the geometry is determined. I do know that it's all kind > of moot these days anyway because of sector based addressing but that > leads to one other question: given sector based addressing why does > fdisk even bother displaying a geometry any more ? Doesn't it just serve > to confuse? That's because fdisk is/was mostly legacy code, we are currently updating the program. Cheers, Davidlohr > > # fdisk /dev/sda > Welcome to fdisk (util-linux 2.21.2). > > Changes will remain in memory only, until you decide to write them. > Be careful before using the write command. > > > Command (m for help): p > > Disk /dev/sda: 80.0 GB, 80026361856 bytes > 224 heads, 56 sectors/track, 12460 cylinders, total 156301488 sectors > Units = sectors of 1 * 512 = 512 bytes > Sector size (logical/physical): 512 bytes / 512 bytes > I/O size (minimum/optimal): 512 bytes / 512 bytes > Disk identifier: 0xc4c4122e > > Device Boot Start End Blocks Id System > /dev/sda1 * 56 501759 250852 83 Linux > /dev/sda2 501760 156298239 77898240 8e Linux LVM > > Command (m for help): q > > Many thanks for your time, > John Lane. > > > > -- > To unsubscribe from this list: send the line "unsubscribe util-linux" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
