[clug] current Intel i3 and i5 processors with "VT-x" support for Virtualisation.

Hal Ashburner hal at ashburner.info
Sun Mar 10 06:50:15 MDT 2013

Not what you're asking, but you know that you can use a lot more than 4 gig
physical ram on a 32 bit system. PAE = physical address extensions needs to
be configured in your kernel to do it. You can't use more than 4G in a
single application with a 32 bit virtual address space. But unless you're
trying to hold a massive database in memory or something whacky like that,
you're unlikely to want to use 4G on a single application. (Does anyone
disagree with that claim? Please speak up!)

x86 going 64 bit is a less than ideal tradeoff for most of us. We get more
architectural registers which is good and allows compilers to optimise in
ways that the cpu register renaming can't because the cpu can't know what
the code is actually trying to get done. But on the down side every pointer
is double the size which effectively makes your caches smaller (more
capacity cache misses than 32 bit) which slows you down.

The linux x32 guys are trying to solve this, apparently by using all the
x86-64 registers, (rax, rbx, rcx, rdx, rdi, rsi, rbp, rsp as usual, plus r8
- r15 and the faster function calls, no system call args on the stack etc.
that this buys you) but keep the virtual address space to 32 bits so
pointers are 32 bits in size meaning less capacity cache misses. I haven't
looked to closely at it yet to see how they're going and if a debian
release of this new architecture is imminent, or even if there are numbers
being produced to show that this is a worthwhile optimisation.

Having said that my rule of thumb has always been the biggest cache I can
get for the budget and everything else is largely irrelevant in cpu
selection. People around here might know why I'm wrong and what works
better. (Linux support for chipset & graphics card tends to be important
and something I'd look at first, but also I've found flash disk makes a the
kind of performance difference I find noticeable as compared to selecting
model x vs model y of cpu, the results of which I usually don't notice so
much either way). Also consider required fan noise to keep it all cool and
so on.

For a laptop, I scour the laptop reviews with a view to getting optimal
battery life & least pain in running linux and having a working suspend,
which usually implies intel graphics. Usually there isn't much choice in
cpu once you've settled on a laptop make and model.

On 10 March 2013 14:04, steve jenkin <sjenkin at canb.auug.org.au> wrote:

> I just looked up the Intel site and it seems to say that all i3 and i5
> processors support their "VT-x" virtualisation instructions, while Atom
> and Centrino, which may be used in laptops, do not.
> <http://ark.intel.com/Products/VirtualizationTechnology>
> The VM systems I've used work better with virtualisation instructions
> like "VT-x" and the AMD equivalent.
> In considering processors for Desktop PC's, what features do CLUGers
> commonly select for? i.e. what do you find is worth paying for, or not?
> Running VM's on a PC is now common & extremely useful - and seems within
> reach of all budgets.
> Is this right?
> Have I missed something basic?
> [like '32-bit CPU's are limited to 4GB RAM']
> I'm asking so when *I'm* asked "what PC should I buy" I can answer
> without misleading the person.
> Thanks in Advance.
> steve
> --
> Steve Jenkin, Info Tech, Systems and Design Specialist.
> 0412 786 915 (+61 412 786 915)
> PO Box 48, Kippax ACT 2615, AUSTRALIA
> sjenkin at canb.auug.org.au http://members.tip.net.au/~sjenkin
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