Boot2 loading process

Jan Pfeifer jan.pfeifer at
Sat Oct 14 18:42:03 PDT 2006

Thanks for the reference Jerry, you are right, from the docs:

boot0: saved into MBR, loads boot2 (the boot1 being the floppy version of it)

But still, according to the docs, boot0 loads only 512 bytes of it.

So thanks for the note Valentin, I understand then that boot0 loads 15 records, that is 7.5kb.

many thanks again,

- jan

ps.: the docs also mentions that slices are the FreeBSD jargon for partitions, sorry.

----- Original Message ----
From: Jerry McAllister <jerrymc at>
To: Valentin Nechayev <netch at>
Cc: Jan Pfeifer <jan.pfeifer at>; freebsd-questions at
Sent: Saturday, October 14, 2006 6:15:55 PM
Subject: Re: Boot2 loading process

On Sat, Oct 14, 2006 at 09:30:53PM +0300, Valentin Nechayev wrote:

>  Sat, Oct 14, 2006 at 09:41:01, jan.pfeifer wrote about "Boot2 loading process": 
> > I was reading through the architecture handbook ( about the boot process, and something strange caught my attention.
> >  According to the docs boot0 loads only the first record of the partition, that is 512bytes. But boot2 in my 4.11 freebsd has > 7K in size -- what makes sense, considering the amount of things it does and that it links btxld.
> Name it "slice", not "partition".
> > So my question is: where does the rest of the boot2 binary is located and how is it loaded ?
> You skipped boot1 from attention. boot2 is loaded by boot1, not boot0.

Not according to that piece of architecture documentation that was quoted.

It says that boot1 is used only with floppy boots.

So, either the question remains or that oiece of doc is incorrect.



> boot1 resides in first block of FreeBSD slice (or whole disk in dedicated
> partitioning). It reads MBR, detects first active FreeBSD slice (or first
> FreeBSD slice if none active), loads first 8K from its (they are boot1
> + disklabel + boot2) and passes control to boot2. boot2 is placed in
> blocks 2-15 of the FreeBSD slice.
> > thanks in advance for any answers!
> -netch-
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