Re: [gentoo-user] AHCI/IDE-question

Mark Knecht <markknecht@×××××.com> [11-01-21 21:04]:
> On Fri, Jan 21, 2011 at 11:40 AM,  <meino.cramer@×××.de> wrote:
> <SNIP>
> > Hi Mark,
> >
> <SNIP>
> > I thought (which implies "I dont know for sure"), that the BIOS do
> > enable/disable certain features, the kernels reads that settings and
> > act accordingly -- but definitely this is not true for all settings.
> >
>
> Certainly true for some hardware, like clocks, etc.
>
> For disk controllers AFAIK the goal is to give the boot loader a
> chance to boot. After that it doesn't, in general, matter what the
> BIOS did.
>
> For instance, modern SATA controllers use DMA. BIOS and older
> operating systems like DOS didn't know much, if anything, about DMA,
> so BIOS leaves that turned off. The kernel turns that on.
>
> > Does the contents of a harddisk differ when written with AHCI
> > compared to a disk which is written with IDE?
> >
>
> TTBOMK no. Other things like file system type, etc., change what's on
> the disk, but the disk store so many bytes/sector and that's just the
> way it works.
>
>
> > If NO _AND_ only the kernel sets the AHCI- odr IDE-protocol, then
> > the harddisk should be readable in either case.
> >
>
> Certainly, which is why you could build this system using AHCI and
> then move it to some other system and read the disk using DOS.
> (Assuming DOS could understand the file system like FAT, etc.)
>
> > If the BIOS _and_ the kernel settings are defining, how to talk
> > to the disk, then it may happen, that there is only the "sound of silence"
> > between kernel and hardware if before the BIOS set up the SATA-chips
> > differently to what the kernel wants to talk.
> >
>
> BIOS sets up the system hardware so the boot loader can get the kernel
> image off the disk. The kernel is read into memory using these
> settings. At that point there aren't any more disk reads for a while.
> The kernel executes and starts resetting the hardware through driver
> loads, etc. This is why one controller could be set to use a SATA
> Drive by itself or RAID.
>
> > But again, these are only thougts drifting in the dark.
> >
> > I tried to shed some more light (for getting greater shadows ;) )
> > by posting my question here... ;) 8)
> >
> > May be I should do some more stupid things??? ;)
> >
>
> Ain't no such thing a stupid question. Only thing to do when
> experimenting is ensure you aren't risking data you care about. I
> would do these experiments on a new clean system. I would not do them
> on a system that has stuff I care about unless I had known good
> backups.
>
> > Thanks again for your help and your words, Mark!
> > Have a nice weekend!
> > Best regards,
> > mcc
> >
>
> You too sir!
>
> Cheers,
> Mark
>


Last thing which remains is: Why does the help of the kernel says
to both AHCI-settings: "If unsure, say N"... ?