[ubuntu-uk] Computer restarts on shutdown

[Liam Proven]

On 17 February 2014 13:42, Pete Smout <smoutpete at gmail.com> wrote:
> Good to know..... I can revive my ancient laptop that always moans about
> pae!


Don't misunderstand me.

PAE is a feature of some x86-32 chips that enables them to access more
than the 32-bit limit of 3-and-a-bit gig of RAM by paging memory above
the 4GB boundary into space below it. It works in exactly the same way
as LIM 4.0 spec Expanded memory worked in the era of MS-DOS, if you
remember that.

If not, read the Wikipedia page. It's good. I wrote it. :)

You need a CPU with the PAE feature enabled for it to work. This means
that kernels compiled with PAE support turned on will not boot on CPUs
that do not have PAE.

If you boot a non-PAE 32-bit kernel, it can only access up to 4GB RAM,
no more. And since 256MB-768MB or more is reserved for your graphics
card's framebuffer & other I/O, that means you get 3-and-a-bit gig.
How much the extra over 3GB is depends on your particular combination
of motherboard chipset and peripherals, including built-in ones.

Enabling PAE means that a 32-bit chip can get at memory above 4GB so
your 32-bit kernel can use 6 or 8 or 16 gig of RAM, but only in little
chunks paged in below the 4GB boundary. You can't have bigger chunks
than that 3-and-a-bit gig. (Actually much smaller but that gets
complicated real fast.) You can't run bigger programs, or programs
that manipulate many gigs of data, any more than any other 32-bit
chip. You just get more chunks.

So it's no replacement for a 64-bit CPU running a 64-bit OS if you
need lots of memory.

But only if your CPU supports PAE. The early-model Pentium M doesn't.
Many Celerons don't either.

And all Ubuntu releases /after/ 12.04 /require/ PAE and won't boot at
all on a CPU that doesn't have PAE.
If you have machines that don't support PAE, the backport kernels won't help.

Where they help is, for example, the laptop I just got for my mum. It
had 2GB RAM. I put some hand-me-down  RAM from a friend in it, for a
total of 4GB, the max it will take.

But it's running 32-bit Mint 13. So it could only access 3.4GB of it.

I installed linux-image-generic-saucy-backport-pae and now the PAE
kernel can see and use all 4GB of RAM. But it will only be used for
cache.

(I also enabled tmpfs for /tmp as a bit of a speedup.)

But since she only runs 1 app - the Simplicity Envelope - that will be fine.

--
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