[Novalug] adventures with linux on low-cost laptops
Bryan J Smith
b.j.smith@ieee.org
Sun Feb 28 22:22:20 EST 2016
pereira via Novalug wrote:
> It doesn't have a normal BIOS
Legacy PC 16-bit BIOS has severe limitations. Beyond the fact that
it's PC-only, and originally designed for only 20/24-bit DOS
addressing/extensions, it's run into severe limitations even with
32-bit extensions.
E.g., 16-bit BIOS Int13h Disk Services cannot target, during boot,
more than 32-bit sectors, so it is limited to 2TiB disk sizes.
> but something called UEFI
Every PC platform ships with 64-bit uEFI today, period. However, most
ship Compatibility Support Modules (CSM) so select, legacy PC 16-bit
BIOS services can be provided, such as BIOS Int10h Video Selection,
BIOS Int13h Disk Services, etc...
> (there was some discussion on the list about uEFI in another context:
No, it was the exact same context actually. ;)
The 64-bit "native" uEFI Storage boot _requires_ the system to be
setup with an EFI System Partition and the actual "boot information"
set in the firmware itself, *never* on-disk (_no_ "boot sectors" at
all). It's virtually impossible to "switch back'n forth" as the
boot/OS is setup completely different.
This is something a lot of people run into issues trying to do, and I
have to come in and radically change their OS to change the boot.
Usually a rescue mode is required, and often a change of the disk
format (or at least a partition).
In the case of dual-booting Windows and Linux, they _must_, _both_ use
the _same_ boot mode.
> I don't know what it is except trouble
64-bit uEFI is what Intel-based Mac has long used (originally started
with 32-bit uEFI), and Windows Vista and later supports, while
Microsoft _requires_ all Windows 8+ systems to ship with.
64-bit uEFI is also what aarch64 (64-bit ARM) is standardizing for
Enterprise Linux, and will finally make ARM a more commodity platform
for end-users.
> but eventually we managed to go to a BIOS
You mean you enabled Legacy CSM modules in uEFI, so it emulated some
BIOS services.
> and start diddling to make it double-boot, Linux/Windows 8.1.
> That never worked.
Correct, because you can_not_ switch Windows 8.1 from 64-bit "native"
uEFI Storage boot to 16-bit legacy BIOS Int13h Disk Services. It has
to be _re-installed_. It's exceedingly _difficult_ to do it with
Linux too, although adding a "BIOS Boot Partition" solves the issue
for GRUB.
That said ...
I have dual-booted over _100_ uEFI systems with Windows and Linux now.
I have _never_ had an issue dual-booting ... _ever_. uEFI systems
_solve_ 99% of the issues with dual-booting. However, you have to
understand how uEFI works. If you're ignorant, you're likely to screw
up your system.
I've had to "fix" lots of those because geeks assume how things work.
> So, we decided to nuke Windows and go pure linux.
Too bad. I could have easily done it. I do it all-the-time, even
with Secure Boot.
> After many mysterious steps that we could not possibly remember,
> we managed to put Xubuntu on it. It works, thanks to Roger. I could
> even install a whole slew of applications, through a script that
> remembers which ones I have on my main machine.
> The battery on this refurbished machine seems to hold up more
> or less well, but its life is still disappointing to me. I don't know what
> to expect from a modern, new, low-power laptop, but this ASUS
> gives me maybe 2 hours runtime.
Might be the lack of driver support for the chipset/SoC power
management. That happened with a lot of the AMD APU units, even some
Intel Atom solutions (including Celeron/Pentium "J" and "N" models,
that are actually Atom) in the past.
> One lesson: get patient, helpful expertise to assist. Thank you, Roger!
> Another lesson: with refurbished laptops, inquire about the battery.
> Thanks to the various discussions on the list, in particular Brian
> whose sleuthing got me to purchase one more laptop than any
> sane person can use at the same time.
Again, I've yet to _ever_ have an issue with native uEFI dual-boot.
If it works with Windows, it _will_always_ work with Linux.
I've only found some older firmware doesn't do full uEFI.
So those won't boot Windows in native uEFI Storage mode either.
--
Bryan J Smith - http://www.linkedin.com/in/bjsmith
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