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Running XP on a 64bit processor computer



 
 
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  #1  
Old November 20th 17, 10:59 PM posted to microsoft.public.windowsxp.general
No_Name
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Posts: 177
Default Running XP on a 64bit processor computer

I have a computer which originally came witt Vista. It's a 64bit
machine. I got it with XP Pro SP3 installed. I know that XP is 32bit.
I'm a little puzzled about this. Can XP (or any 32bit OS) run on a
computer that has a 64bit processor?

(I know you cant do it the other way. You cant run a 64 bit OS on a 32
bit machine).

Does running a 32 bit OS on a 64bit machine work any better or worse
than it does using an actual 32 bit computer?

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  #3  
Old November 21st 17, 03:27 AM posted to microsoft.public.windowsxp.general
J. P. Gilliver (John)[_4_]
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Posts: 2,679
Default Running XP on a 64bit processor computer

In message , MikeS writes:
On 20/11/2017 21:59, wrote:
I have a computer which originally came witt Vista. It's a 64bit
machine. I got it with XP Pro SP3 installed. I know that XP is 32bit.
I'm a little puzzled about this. Can XP (or any 32bit OS) run on a
computer that has a 64bit processor?
(I know you cant do it the other way. You cant run a 64 bit OS on a
32
bit machine).
Does running a 32 bit OS on a 64bit machine work any better or worse
than it does using an actual 32 bit computer?

Yes provided you mean an x64 bit processor which is an extension of the
32 bit architecture.
The advantage of using a 64 bit OS version (such as the final version
of Win XP - Pro 64 bit) was mainly a larger address space allowing 4
GB RAM.

You didn't answer the last part of James's question - "Does running a 32
bit OS on a 64bit machine work any better or worse than it does using an
actual 32 bit computer?"

(FWIW, I suspect it'll run about the same, other than that the 64bit
machine is probably faster and may have more cores - but those are not
specific to it's 64bitness. There _may_ be a few cases where the
firmware in the processor makes a few operations work better, but if
any, I suspect this is an insignificant proportion of the time.)
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

All's well that ends.
  #4  
Old November 21st 17, 04:00 AM posted to microsoft.public.windowsxp.general
Paul[_32_]
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Posts: 11,873
Default Running XP on a 64bit processor computer

wrote:
I have a computer which originally came witt Vista. It's a 64bit
machine. I got it with XP Pro SP3 installed. I know that XP is 32bit.
I'm a little puzzled about this. Can XP (or any 32bit OS) run on a
computer that has a 64bit processor?

(I know you cant do it the other way. You cant run a 64 bit OS on a 32
bit machine).

Does running a 32 bit OS on a 64bit machine work any better or worse
than it does using an actual 32 bit computer?


The CPU has two modes.

Mixed mode supports 32-bit and 64-bit instructions at the same time.
The processor knows which are which, via the OPcode decoder. It
knows how much of each to "suck in", based on that.

32-bit and 64-bit OSes both work in mixed mode.

So yes, WinXP x32 runs on a 64-bit CPU, as long as the
CPU is in mixed mode. And it is.

*******

I have one table somewhere, which claims these CPUs also
have a "pure" 64-bit mode. Why anyone or any hardware
company would think of invoking that, is anyones guess.
As the Mixed Mode is so much nicer. There is at least
one Linux distro, that runs in pure 64-bit mode. Maybe
they did it as a bar bet or something.

*******

On Core2 processors, the x32 instructions execute faster
than the x64 instructions. This is due to a packing
mechanism the CPU uses. It has some 64 bit plumbing, which
can suck in two 32 bit things at a time. That packing
mode adds maybe 5% more performance (for certain programs)
to the CPU. When you switch to the 64-bit OS, you have
to balance any (slight) efficiency gain from 64-bit wide
data handling, versus the loss caused by the lack of packing.

More modern processors no longer have that distinction,
and then 64-bit wins as long as the data you need to
handle is really wide.

For counting loops, many counting loops use small numbers.
The 32-bit storage handles them just fine. Using a 64-bit
OS, doesn't make such counting work any better.

However, if you do arbitrary precision arithmetic with
GMP library, the 64-bit processing makes a big difference.
Code run in 64-bit mode is 70% more efficient than code
run in 32-bit mode. I ran some C code for Mersenne Primes
on top of GMP and benchmarked it. That's the most speedup
I know of, because of using a 64-bit OS. For many other
things, the 64-bit OS buys you... sweet nothing.

The main benefit of 64-bit, is allowing a program
to use more than 2GB of memory. Like the Firefox
people who want to eat all the RAM in the computer.
That's why they're pushing the 64-bit version. I sometimes
use 32-bit versions of programs, for the express
purpose of "containing" them. It's a kind of memory
quota, and prevents runaway behavior.

*******

The only thing that doesn't work, is installing a
64-bit OS on a 32-bit-only CPU. And you know that
already. The installer disc would tell you early on,
it cannot be done. For example, my AthlonXP CPU
is 32-bit only, which means half the DVDs in the
house cannot be used on it (for OS installs). A
couple of my early Pentium 4 processors are in
that predicament (32-bit only).

*******

The single biggest issue with putting WinXP on a
new machine ? The AHCI driver for the HDD interface.

If you get a blue screen and an "Inaccessible Boot Volume"
error, that's what is blocking it.

You need to press F6 early in the install and offer
a floppy diskette with the AHCI driver. WinXP
has *some* in-box drivers, so if you configure the
BIOS correctly, there won't be an issue. If you leave
it in AHCI... there will be an issue. If you have
the small Intel TXTSETUP.OEM file set, you can fix
it via F6. The prompt appears at the bottom of the
screen, early in the WinXP install process.

I think my laptop is stuck in AHCI mode, so
that's the first issue I'd have to deal with.

You can also slipstream an AHCI driver into a
WinXP installer disc, and then when installing,
you don't need to press F6 and you don't need
a floppy drive. So that's how heroic WinXP users
running newer hardware can do it.

Paul
  #6  
Old November 28th 17, 07:16 AM posted to microsoft.public.windowsxp.general
Paul[_32_]
external usenet poster
 
Posts: 11,873
Default Running XP on a 64bit processor computer

Steve Hayes wrote:
On Mon, 20 Nov 2017 15:59:04 -0600, wrote:

I have a computer which originally came witt Vista. It's a 64bit
machine. I got it with XP Pro SP3 installed. I know that XP is 32bit.
I'm a little puzzled about this. Can XP (or any 32bit OS) run on a
computer that has a 64bit processor?


XP comes in 32 and 64-bit versions.


Yes, but the 64-bit XP version isn't all that good. Back in the
era, it lacked drivers.

https://en.wikipedia.org/wiki/Windows_xp

"Service Pack 3 is not available for the 64 bit version
of Windows XP, which is based on the Windows Server 2003 kernel."

That OS has slightly different roots, than the 32-bit version.

And support for environments like that, depends on the number
of people adopting the product. If there aren't many
users for an OS variant, you can have problems getting
programs to support installation on it, and so on.

I think the same was true for Windows Server 2003 users. Hardware
back in that time, might lack an entry in the INF file, to get
the driver to install.

Those users end up "whining a lot" while using it :-)

Paul
 




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