Upgrading grub, MBR vs. first block in a partition
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From: Robert Nichols on 5 Feb 2010 21:49 In article <e9oq37-vdi.ln1(a)psd.motzarella.org>, Peter D. <p13(a)g-node.com.au> wrote: :on Mon, 1 Feb 2010 03:09 am :in the Usenet newsgroup comp.os.linux.hardware :Robert Nichols wrote: : :> In article <fb1f37-nv1.ln1(a)psd.motzarella.org>, :> Peter D. <p13(a)g-node.com.au> wrote: :> :on Fri, 29 Jan 2010 03:19 pm :> :in the Usenet newsgroup comp.os.linux.hardware :> :Robert Nichols wrote: :> [very big SNIP] :> :> And BTW, if you turn off "DOS Compatibility Mode" when partitioning :the :> :> disk, then those 62 sectors are not left free and there is nowhere :that :> :> stage 1.5 can be embedded. :> : :> :So, if I ever find a partitioning tool that says, "only used by MS" then :> :it is a bug. It could do with a better name anyway. :> :> Come again???? That statement makes little sense. : :Sorry. I'll try again. : :Somewhere in the dim, dark, unreliable recesses of my mind I have the :memory of deliberately not using the DOS compatible mode, because as :a Linux user, I thought that I had no use for it. I prefer LiLo, but :recent discussions here indicate that for the reliable use of GRUB, :DOS compatible mode is highly desirable. i.e. It is a mistake for :for a Linux user to not use DOS compatible mode. : :As I now understand things any documentation that suggests, directly :or indirectly, that DOS compatible mode is something that only DOS :(or Windows) users need worry about is wrong. If a user interface :causes a user to select an option that makes a computer unbootable :I would suggest that that is a bug. : :> The function of DOS :> Compatibility Mode is to ensure that each partition's start of data is :> at the start of a track, which was a requirement back in the days of :> MS-DOS** and C/H/S disk addressing. : :Original purpose, but not only use. : :> The effect is that wherever there :> is a primary or secondary partition table, the remainder of that track :> is left unused and the partition begins at the start of the next track. :> In today's world of virtual geometries and LBA disk addressing there is :> really no need for that, but various boot loaders, disk management :> tools, and the like (viruses, too) do make use of that free space. : :I'm with you. : :> Some partitioning tools ('fdisk' is one) allow you to turn off DOS :> Compatibility Mode (it is ON by default) and have the partition start at :> the sector immediately following the partition table, thus reclaiming :> that "wasted" space (maximum of 62 sectors -- not a big deal with :> today's disk sizes). So, which is it that you consider a bug: :> partitioning tools that leave that "MS-only" free space (that would be :> the default for _all_ of them), or tools that provide the option to :> reclaim it? :> :> ** I have no idea whether recent versions of MS-Windows still require :> that file systems begin on a track boundary. : :I would consider it a bug to misinform the user such that they are :tempted to do something that can make their system unbootable. A DOS :mode does not seem very important to this Linux user. : :On my current system cfdisk has a toggle labelled "Maximise" rather :than DOS compatibility. I think that the name change is a big :improvement, although I found no reference to GRUB in the man pages. Ahhh, yes. Now I understand, and agree about options whose names imply that their effect is only needed for MS OSs. Both 'fdisk' and 'cfdisk' at least give notice that changing that toggle is an "experts only" function -- gives people a chance to discover the limits of their expertise. -- Bob Nichols AT comcast.net I am "RNichols42"
From: Tecknode on 16 Feb 2010 16:38
Peter D. wrote: > on Mon, 1 Feb 2010 03:09 am > in the Usenet newsgroup comp.os.linux.hardware > Robert Nichols wrote: > >> In article <fb1f37-nv1.ln1(a)psd.motzarella.org>, >> Peter D. <p13(a)g-node.com.au> wrote: >> :on Fri, 29 Jan 2010 03:19 pm >> :in the Usenet newsgroup comp.os.linux.hardware >> :Robert Nichols wrote: >> [very big SNIP] >> :> And BTW, if you turn off "DOS Compatibility Mode" when partitioning > the >> :> disk, then those 62 sectors are not left free and there is nowhere > that >> :> stage 1.5 can be embedded. >> : >> :So, if I ever find a partitioning tool that says, "only used by MS" then >> :it is a bug. It could do with a better name anyway. >> >> Come again???? That statement makes little sense. > > Sorry. I'll try again. > > Somewhere in the dim, dark, unreliable recesses of my mind I have the > memory of deliberately not using the DOS compatible mode, because as > a Linux user, I thought that I had no use for it. I prefer LiLo, but > recent discussions here indicate that for the reliable use of GRUB, > DOS compatible mode is highly desirable. i.e. It is a mistake for > for a Linux user to not use DOS compatible mode. > Be aware the real issue is your system BIOS being able to access a hard drive to boot. The MBR specification is to accommodate the 8bit BIOS access requirements/limitations. It is NOT related directly to what OS you are running, ONLY to the BIOS, AND its location MUST be Trick-0, Sector-0 (aka LBA Sector-0). See: http://en.wikipedia.org/wiki/Master_boot_record |