Dan McGhee wrote: > On 12/18/2013 04:09 PM, akhiezer wrote: >>> Date: Wed, 18 Dec 2013 16:00:11 -0600 >>> From: Dan McGhee <beesn...@grm.net> >>> To: LFS Support List <lfs-support@linuxfromscratch.org> >>> Subject: Re: [lfs-support] LFS 7.4 - Chapter 8.4 - GRUB >>> >>> [...] But, AFIK, the user must *make* >>> the partition behave with the GUID's. [...] >> >> Not quite sure what you're meaning there, Dan - apols if/that am being dense: >> elab if poss? (No probs of course if not.) > No prob anywhere. > >> [...] But, again AFIK, if the firmware >> is MBR based, you're still limited to four primaries. >> >> IIUYC: no; e.g. got an old (a testing-machine) p4 on a supermicro p4spa+ (or >> sim) mainboard, running modern blfs/slack1337, with disks partitioned with >> GPT and each disk has ~16 partitions. No non-/pre-GPT stuff in sight, no >> UEFI stuff in sight, and all goes just fine. > This is what I meant. The user needs a gpt capable partitioning tool to > *make it so* on an "older" machine. >> And, again IIUYC re 'primaries': no such concept in GPT, at least not in >> pre-GPT sense; and in pre-GPT sense, yes, the spec only allows for 4 >> primaries >> anyhow.
> This is another source of misunderstanding. May be too strong a word. > It's all vocabulary. MSDOS MBR's don't have the "bit length" to > physically support more than what is know as a "primary," as opposed to > "extended" partition. Not quite. The MBR handles 32-bit words. That gives addressing of up to 4G of 512-byte partitions. That's how you get the 2T limit. The limit could be higher if the block size is 4K, but that creates a lot more problems for the legacy BIOS, so it's better to just use GPT that has 128-bit lengths for sector addressing. That's enough for a zetabye or so even with 512-byte sectors. Try to run fsck on that! :) Extended partitions have the same limitations as MBR primary partitions, but there are just in a linked list and not an array. > I don't have a "pdf reader" set up on my new LFS > yet so I can't refer to an article I'm thinking of. But if I remember, > the "old" MBR is 16 bit. The UEFI bios firmware is 128 bit. There, of > course, is a limit to the number of partitions, but it's large. :) I think it is 128 partitions by default, but it can be made to handle more. Another difference is that classical systems start the first partition at the 2nd 'physical' track (often faked in drives) of 63 sectors. That leaves about 31K for the GRUB2 code. For GPT, we make a raw boot partition for grub, usually 1Mb, that give it lots of space for expansion, but is negligible compared to the whole disk drive. From our perspective, the only thing that is needed is to load one 512-byte sector into memory and execute it. The bootstrapping continues from there and only needs very basic BIOS calls to load other sectors into memory. Of course after booting, the kernel does not need the BIOS/UEFI at all. -- Bruce > I find this subject fascinating, but until I get my new system where I > want it, I'm hampered by jumping back and forth between Ubuntu and LFS. > So I'm just still building until then. > > Thanks for responding akh, you've provided me with some more precision > in my ability to talk about this. > > Dan > -- http://linuxfromscratch.org/mailman/listinfo/lfs-support FAQ: http://www.linuxfromscratch.org/lfs/faq.html Unsubscribe: See the above information page
