fdisk -ul why does first partition start at sector 63?

nickamon · 07-17-2009, 03:12 PM

Hi All,

I am learning more about building disk images using fdisk and in the process decided to view the partition settings of my primary disk. I issued the fdisk -l and it showed that my first partition started on cylinder 1. Then I did a fdisk -ul and it shows that the first partition starts at sector 63. My question: Why doesn't it start at sector 1, skipping the first sector for the MBR?

Thanks,

Nicholas

jefro · 07-17-2009, 03:38 PM

The Ranish site has or had great info on how partitions work. Might look that up.

There are still areas before the partition that are used.

You could use it as raw device but most people don't.

catkin · 07-17-2009, 03:41 PM

Hello nickamon

It's probably a hangover from the DOS specification. According to http://www.pixelbeat.org/docs/disk/, DOS required that partitions began at the start of a cylinder. Whatever the reason, it has been very handy for grub which uses the "wasted" 63 cylinders to store a much more powerful boot loader than could fit in the MBR alone.

Best

Charles

nickamon · 07-17-2009, 04:05 PM

Thanks jefro and catkin. The information you provided is exactly what I needed. Thanks again.