Which is the best choice, pae or x64?

[Rofail Qu]

Very detailed description. Thanks a lot.
I think 64-bit ubuntu is my best choice for almost all softwares installed
on this computer are open source, and its major use is science computing.

Yes. I really ever confused x86-64 with VT or AMD-V.
Once, I ever help one install a 64-bit Windows7 in VMWare under Windows XP.
I found that her pc's bios has VT options. And could install the
64-bit Windows7 VM only if i enable it. From then on, I thought I must
enable the VT options when i want to install a 64-bit OS on a EMT64
cpu(not only as VM).

So, I don't need Intel VT enabled to run an *64-bit* VM under 64-bit
ubuntu (not like case of run 64-bit Windows7 under 32-bit Windows XP),
is that right?

Two more question, If I enable VT option, can VirtualBox automatically
benefit from it when i run a 64-bit VM under 64-bit ubuntu?
Is 64-bit virtualbox in ubuntu's source good enough?
I am now using VMWare Workstation under ubuntu, but performance is poorly.

2010/9/25 Liam Proven <lproven at gmail.com>:
> 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
> Email: lproven at cix.co.uk • GMail/GoogleTalk/Orkut: lproven at gmail.com
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