[CentOS] Analyzing the MBR

Thu Jun 5 20:50:40 UTC 2014
m.roth at 5-cent.us <m.roth at 5-cent.us>

Timothy Murphy wrote:
> 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?
Or what might be happening is that it's leaving 1M or so, to align the
partitions properly for best access times. Certainly, I've been doing that
manually, or in our kickstart file, for several years now.