John R Pierce wrote: > On 6/5/2014 10:47 AM, Timothy Murphy wrote: >> Is this strictly true - that only the MBR is read at boot-time? > > the MBR has two elements. > > A) the boot code, which is read and executed by the BIOS at boot time, > only on the boot drive > and > B) the master partition table, which is read on any drive when its > inserted That doesn't really answer my question; I know (roughly) what the MBR, ie the first 512 bytes, contains. But I notice that my laptop, for example, leaves 64 sectors for something at the start of the disk; and when I get the first 2048 bytes with sudo dd if=/dev/sda of=sda.mbr bs=2048 count=1 I see that there is plenty on the disk after the first 512 bytes. (Admittedly Windows might have written that, as I have a Windows partition.) But does Linux ever write anything in bytest 513-1024, for example? Does grub2 write more than CentOS grub? It seems to me to be difficult to have CentOS and Fedora as alternative OSs on the same machine? -- Timothy Murphy e-mail: gayleard /at/ eircom.net School of Mathematics, Trinity College, Dublin 2, Ireland