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Re: OS for 4GB RAM

 
 
sandy58
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      04-02-2010
On Apr 2, 7:55*pm, "James D. Andrews" <(E-Mail Removed)> wrote:
> Do I need to use a 64-bit OS with 4GB RAM, or will 32-bit work? *I was
> reading today that the 32-bit will only support 3GB. *Don't know how true
> that is.
>
> I suppose it would be nice to know before I go and buy an OS.
>
> --- news://freenews.netfront.net/ - complaints: (E-Mail Removed) ---


32-bit won't use 4gb ram. 3gb is about it.
64-bit will use as much as you can get in.
 
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Jeff Strickland
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      04-03-2010

"sandy58" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
On Apr 2, 7:55 pm, "James D. Andrews" <(E-Mail Removed)> wrote:
> Do I need to use a 64-bit OS with 4GB RAM, or will 32-bit work? I was
> reading today that the 32-bit will only support 3GB. Don't know how true
> that is.
>
> I suppose it would be nice to know before I go and buy an OS.
>
> --- news://freenews.netfront.net/ - complaints: (E-Mail Removed) ---


32-bit won't use 4gb ram. 3gb is about it.
64-bit will use as much as you can get in.

<JS>
I'm using all 4G of RAM in my machine. I have 32-bit XP Pro.



</JS>





 
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gnu / linux
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Posts: n/a
 
      04-03-2010
On Apr 2, 7:12*pm, "Jeff Strickland" <(E-Mail Removed)> wrote:
> "sandy58" <(E-Mail Removed)> wrote in message
>
> news:(E-Mail Removed)...
> On Apr 2, 7:55 pm, "James D. Andrews" <(E-Mail Removed)> wrote:
>
> > Do I need to use a 64-bit OS with 4GB RAM, or will 32-bit work? I was
> > reading today that the 32-bit will only support 3GB. Don't know how true
> > that is.

>
> > I suppose it would be nice to know before I go and buy an OS.

>
> > --- news://freenews.netfront.net/ - complaints: (E-Mail Removed) ---

>
> 32-bit won't use 4gb ram. 3gb is about it.
> 64-bit will use as much as you can get in.
>
> <JS>
> I'm using all 4G of RAM in my machine. I have 32-bit XP Pro.
>
> </JS>


32 bit will use most all of the 4 GB
 
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Jeff Strickland
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      04-03-2010

"gnu / linux" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
On Apr 2, 7:12 pm, "Jeff Strickland" <(E-Mail Removed)> wrote:
> "sandy58" <(E-Mail Removed)> wrote in message
>
> news:(E-Mail Removed)...
> On Apr 2, 7:55 pm, "James D. Andrews" <(E-Mail Removed)> wrote:
>
> > Do I need to use a 64-bit OS with 4GB RAM, or will 32-bit work? I was
> > reading today that the 32-bit will only support 3GB. Don't know how true
> > that is.

>
> > I suppose it would be nice to know before I go and buy an OS.

>
> > --- news://freenews.netfront.net/ - complaints: (E-Mail Removed) ---

>
> 32-bit won't use 4gb ram. 3gb is about it.
> 64-bit will use as much as you can get in.
>
> <JS>
> I'm using all 4G of RAM in my machine. I have 32-bit XP Pro.
>
> </JS>


32 bit will use most all of the 4 GB



<JS>
That's my point. The person I was replying to said that only 3G is supported
by 32-bit systems.

</JS>





 
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Paul
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      04-03-2010
Jeff Strickland wrote:
> "gnu / linux" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
> On Apr 2, 7:12 pm, "Jeff Strickland" <(E-Mail Removed)> wrote:
>> "sandy58" <(E-Mail Removed)> wrote in message
>>
>> news:(E-Mail Removed)...
>> On Apr 2, 7:55 pm, "James D. Andrews" <(E-Mail Removed)> wrote:
>>
>>> Do I need to use a 64-bit OS with 4GB RAM, or will 32-bit work? I was
>>> reading today that the 32-bit will only support 3GB. Don't know how true
>>> that is.
>>> I suppose it would be nice to know before I go and buy an OS.

>> 32-bit won't use 4gb ram. 3gb is about it.
>> 64-bit will use as much as you can get in.
>>
>> <JS>
>> I'm using all 4G of RAM in my machine. I have 32-bit XP Pro.
>>
>> </JS>

>
> 32 bit will use most all of the 4 GB
>
>
>
> <JS>
> That's my point. The person I was replying to said that only 3G is supported
> by 32-bit systems.
>
> </JS>
>


This depends a lot, on the details.

As JS mentioned via a link at the end of his posting, there is a
hardware feature called PAE, that maps 32 bit addresses to a 36 bit
physical address space. Intel processors and chipsets have had PAE
capability for some time. And PAE allows a 32 bit OS to address up to
64GB of installed memory. (Modern PAE can support more than 36 bits,
so more is possible. For example, on modern AMD processors, it goes
to 40 bits.)

It is possible that some early version of WinXP, still properly supported
PAE. But in later Service Packs, a bit was borrowed for something like NX
(no execute) bit. That was a security feature. At the same time, they
decided it would be fun to prevent PAE from accessing more than 4GB.
I'm a little fuzzy on the details.

There is a discussion about this topic, here. This person hacked an MS
OS, to prove that more than 4GB can be addressed by a 32 bit OS. It works.

http://www.geoffchappell.com/viewer....nse/memory.htm

So, if the OS has PAE neutered, then indeed there might be only
4GB of address space available via the 32 bit OS. From that, the
hardware devices (like the memory on the video card), has to be
addressable. And after all the addresses for the various hardware
busses have been assigned by the BIOS, the remainder is used to
provide access to the memory DIMMs. If you install 4GB worth of DIMMs,
and happened to use an old PCI video card with small resident memory,
you might see reported that you have 3.5GB free. (Bus address space
is assigned in 256MB chunks, and with PCI/AGP or PCI/PCI Express,
you might lose two chunks to start with. Once the actual hardware
rolls over that assignment, another chunk would be mapped in. So
the assignment process has a relatively coarse granularity.)

If you install a couple Nvidia video cards in SLI, with 512MB of
memory on each card, and happen to have 4GB memory installed,
and have the neutered OS running, then the free memory reported
once the OS is running, could be as low as 2.75GB (someone reported
that, on an S939 board). Which negates the purpose of installing
that much memory to begin with. If you had a monster video setup,
you might be better off installing 2x1GB + 2x512MB sticks, for a
total of 3GB dual channel mode. And then, you'd still see the
2.75GB free reported, and would only be losing 0.25GB.

Or, you could use a 64 bit OS, and have it all.

In terms of the memory configuration, a lot of people would choose
to use 2x2GB, as it may support a higher max operating frequency
for the DIMMs. And then take the loss, on whatever amount of memory
is inaccessible by the OS. Using a four stick configuration, might
not clock quite as high.

The details are a bit fuzzy, as to whether there is a good reason
for PAE to not work on WinXP x32. But it would certainly push
sales of alternate OS solutions. (And no, WinXP x64 is not a good
choice. It was a little rough around the edges.)

If you use PAE, one of the limitations would be, that a single
program could not use all the memory on the computer. If you
had 8GB of RAM installed, used a 32 bit OS, you would need
two programs, accessing 4GB each, to use all the memory.
There might even be further restrictions, as to the maximum
memory that any program or process could use (user/kernel split?).
So even if PAE was working, it is a less ideal situation than using a
64 bit OS to solve the addressing limitations. But PAE
does have the advantage, that it has been available in hardware
for a long time. It is only now, that ordinary desktops
can easily reach those memory limits.

http://en.wikipedia.org/wiki/Physical_Address_Extension

"Windows XP Service Pack 2 and later, by default, on processors
with the no-execute (NX) or execute-disable (XD) feature, runs
in PAE mode in order to allow NX. The no execute (NX, or XD for
execution disable) bit resides in bit 63 of the page table entry
and, without PAE, page table entries on 32-bit systems have only
32 bits; therefore PAE mode is required if the NX feature is to
be exploited.

However, "client" versions of 32-bit Windows (Windows XP, Windows
Vista, Windows 7) limit physical address space to the first 4 GB
for driver compatibility and *licensing* reasons, even though these
versions do run in PAE mode if NX support is enabled."

So that tells you, the limitation is artificial.

There are some other things to consider, before making the OS choice.
For example, how much memory does the software you own, want to use ?
I have a copy of Photoshop, that won't go above 1.8GB on a 4GB system.
For the people that own large quantities of memory, I'd be interested
in what exactly they've been able to get out of it. I wasted a couple
hours on the topic and gave up (my machine is back to 2GB now). I
don't seem to have anything which is IMAGE_FILE_LARGE_ADDRESS_AWARE.
I could certainly run a couple different programs, to use the RAM,
such as some VPC2007 sessions. And that is the most likely thing
here, that would benefit from 4GB. For a lot of other stuff, 2GB
is enough for me.

http://en.wikipedia.org/wiki/RAM_Limit

A 64 bit OS, makes some of the issues more transparent. But does
not guarantee that a single program can use all available memory.
For example, if you have a 64 bit executable, running on a 64 bit
OS, that removes the limits. But other combinations could
still have limits, like running existing 32 bit programs on
a 64 bit OS.

"Memory Limits for Windows Releases"
http://msdn.microsoft.com/en-us/libr...78(VS.85).aspx

Paul
 
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