Which is the best choice, pae or x64?

[Liam Proven]

On 25 September 2010 15:28, Rofail Qu <rofail at gmail.com> wrote:
>> An Intel x86 cpu cannot run x64 applications. Your E8400 is NOT a x86
>> cpu. It is an EMT64 cpu. To run x64 applications, you have to use EMT64
> Thanks for target my mistake. In my thought, EM64T is the extention of IA-32,
> not REAL 64 bit.
> so i really want to know is if it could run on a 64-bit ubuntu faster than
> on a pae version.

There is no real difference and I think the previous answer is
confusing and a little unhelpful. Sorry to the poster!

There have been 4 generations of x86 instruction set:
8088 & 8086: 8-bit
80286: 16-bit
80386, 80486, Pentium family, Cyrix 6x86, AMD Athlon, etc: 32-bit, now
usually called "x86" or "x86-32".

Then came the AMD Athlon64 & Opteron family, which introduced x86-64.
This is a 64-bit extension to x86-32.

N.B. Do not confuse this with the Intel Itanium, IA64. Itanium is not
x86-compatible and cannot run x86 code.

Microsoft compelled Intel to licence AMD's extension for the later
Pentium 4 chips and the Core2 and later families. (MICROS~1 was going
to introduce its own, incompatible variant. MS already support x86-64
& refused to support 2 different 64-bit extensions.)

Knowing that Intel was going to have to licence it, AMD, in a fit of
childishness, renamed x86-64 to AMD64. Intel obviously would not use
its rival's name, so renamed it EMT64.

x86-64, AMD-64 and Intel EMT64 are all the same thing. There are tiny
differences but they are completely unimportant.

In theory, x86-64 code runs a little faster than x86-32, because
x86-64 supports twice as many CPU registers, and x86-32 and its
predecessors have  been famously very short of registers for decades.
However, x86-64 code takes a little more space and a little more
memory, so this is a cost, which offsets the benefit of extra
registers. It is a trade-off.

> In fact, i have this pc runs on a pae kernel for years.

PAE is still 32-bit bit. It allows a 32-bit OS to access more than
approximately 3.5GB of RAM but gives none of the benefits of 64-bit
code. However, a 32-bit kernel is slightly more compatible with more
programs than a 64-bit kernel.

Many people advise staying with a 32-bit kernel for greater
compatibility, especially with drivers and other proprietary binary
programs (e.g. Adobe Flash player). FOSS programs can just be
recompiled for 64-bit; closed, proprietary code cannot and you must
wait for the vendor to provide a 64-bit version, if they ever do.

Me, I run 64-bit and have no problems. Flash player works fine. I have
to run Spotify under XP in a VirtualBox VM because Spotify does not
work properly under 64-bit WINE but that is the only problem I have
encountered.

If you have 4GB of RAM, I personally would recommend going 64-bit.

Final note. Do not confuse x86-64 with VT or AMD-V. If you are
interested in virtualisation, this is a separate question: you can use
hardware virtualisation (if your CPU supports it) in 32-bit mode.

However, if you want to run several large VMs, a 64-bit host OS can
allocate more RAM to them than a 32-bit one can.

My CPU does not support hardware virtualisation, sadly, but software
virtualisation in VirtualBox still works fine. I run XP (32-bit
version) under 64-bit Ubuntu all the time and it works flawlessly, and
because I have 4GB of RAM and a 64-bit host OS, I can allocate 2 or
even 3 512MB VMs in VirtualBox and the host Ubuntu system still has
plenty of workspace.

Summary: x86-64 is good. (I prefer to stick to the vendor-neutral
name, it's less confusing.) It works fine and the performance is good.

You don't *need* hardware virtualisation (Intel VT) to run VMs under
Ubuntu. In theory the performance is a little better, that's all.

You don't *need* a 64-bit host to run virtualisation, but actually, it
can help a little bit.

-- 
Liam Proven • Info & profile: http://www.google.com/profiles/lproven
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