Lowell Gilbert <[EMAIL PROTECTED]> writes: > [EMAIL PROTECTED] (Gary W. Swearingen) writes: > > > > Just to be clear: the BIOS can boot from them, as it does in many > > people's Linux setups. > > My use of terminology was a little imprecise, but this statement is > even more so. On no PC-class machine does the BIOS boot *anything* > except the MBR. Linux systems (for example) that boot from extended > partitions do so by using a boot manager that lives on the disk, > somewhere beyond the 512-byte boot sector, but the BIOS knows nothing > about those partitions.
The BIOS doesn't need to know about the partitions to boot from them. When I last used Linux, it's boot code made BIOS calls to access the boot code and kernel on those partitions. (I'm not sure how more recent versions handle it; IIRC, they have disk-aware boot code stored in additional boot records in the first track of the disk which most extant software reserves for boot software.) I agree about the imprecise language; I was, for once, trying to avoid additional pedantry and explanation. I gave people the benefit of the doubt in assuming that they knew that a BIOS does not know about partitions but can still boot from partitions. Rather like how "dd" can copy a filesystem without knowing about filesystems. I also let slide the misuse of "extended partition" (for "secondary partition" or "logical partition"), because I knew what was meant, even though I'm quite sure that the term should only be used for a primary partition which starts with a boot record and some kind of secondary (AKA extended, AKA logical) partitioning scheme, so that, in IBM (or was it MSFT?) jargon, one can have more than four "logical drives". If anyone has a URL for some old IBM or MSFT documents on the subject, I'd like to have it. Or maybe some hard drive standard. > > (FreeBSD would either have to be able (like Linux) to use the same > > secondary-partitioning scheme as IBM did or FreeBSD would have to be > > able to shoehorn its slices in, supporting a tertiary-partitioning > > scheme.) > > That's not really the problem. The boot manager has to know how to > invoke the FreeBSD loader. With the root filesystem in its own > extended partition, and the right set of boot blocks in that > partition, you can boot FreeBSD from an extended partition, without > changing any of FreeBSD's filesystem or slice support. [A number of > people have done it; the only tricky part is that, as I mentioned in > my earlier message, the FreeBSD installer can't do it for you.] So FreeBSD *is* able to use the same scheme as IBM did, as long as you install it with something besides the OS installer; I didn't know that or that FreeBSD would be so easy to "fix". That makes it even harder to explain why it hasn't been done. So could "/" be "s2a" or would it be "s5" or "s5a" or what? Could the extended (primary) partition be "s3c" or would it be "s5c" or what? How would the second secondary partition, say swap, be labeled? To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-questions" in the body of the message
