[ubuntu-uk] VIA Neheima CPU and Ubuntu Server

Liam Proven lproven at gmail.com
Wed May 15 19:07:47 UTC 2013


On 15 May 2013 19:52, Yorvyk <yorvik.ubunto at googlemail.com> wrote:
> On 15/05/13 10:41, Liam Proven wrote:
>>
>> However, if the Via C3 has other issues as well as PAE support, this
>>  may not be enough.
>>
> I believe the C3 doesn't have a full i686 instruction set and requires a
> i589, or lower, kernel. The geode SOC is similar in this respect.

[Nod] I thought it might be  - that's what I meant when I said "has
other issues as well".

I don't think Ubuntu supports raw i386/i486 any more - I'm not 100%
sure. Debian does, though. I am running Debian with an i386 kernel on
the same Thinkpad to which I referred.

However, note that raw i386 support is being removed from the recent
builds of the Linux kernel so soon this will not be an option.
http://www.engadget.com/2012/12/15/linux-to-drop-i386-support-in-the-3-8-kernel/

I think 486 optimisation will still work, though. (The low-level core
of the 80486 is quite different from the 80386 although the
instruction set is identical, barring 1 extra opcode. The 486 is a
pipelined, scalar core. I believe that GCC understands this and can
optimise for it. Whether the kernel will retain 486 support, I don't
know.)

> As I understand it he Pentium M does have PAE but no PAE flag. The
> fake-pae patches /proc/cpu so as as to show this flag as it were.

I don't think this is the case, but I am not certain.

PAE was introduced in the Pentium Pro in the mid-1990s and is
supported in almost every CPU since /except/ the Pentium-M and some
low-end Celerons. I have seen Ubuntu 12.10 refuse to boot on some
Celeron machines with the error that PAE is missing.

I think, technically speaking, that the CPU feature is *disabled*
rather than *missing* but it hardly matters. It's not there and
kernels that require it won't boot except with fake-PAE. This makes
installing a fresh copy tricky, although it can be done: you need to
unpack the ISO onto a USB stick, add an extra kernel (e.g. the 12.04
non-PAE version) and use the replacement kernel.


--
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