Dude, where's my 4GB?

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Postposted on Thu Nov 15, 2007 10:48 am

3,072,000K ought to be enough for anybody. :wink:
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Postposted on Thu Nov 15, 2007 10:50 am

DrDillyBar wrote:3,072,000K ought to be enough for anybody. :wink:


It is actually 3,221,225,472 bytes ;)
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Postposted on Sat Dec 22, 2007 12:58 am

Here's one for you all. I'm running Windows XP Professional x64 on a Biostar 945P-A7A 8.0 Motherboard running Core2 E4400 Intel processor w/ 4GB of ram ... however, it only recognizes 3.25GB. Nothing I've been able to do enable the system to recognize that last .75GB :(

Any sujestions?

Thx for any/all responses.
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Postposted on Sat Dec 22, 2007 1:16 am

Does the BIOS have the option(s) to re-map the memory, and are they enabled?
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Postposted on Sat Dec 22, 2007 1:20 am

DigitalNoob wrote:Here's one for you all. I'm running Windows XP Professional x64 on a Biostar 945P-A7A 8.0 Motherboard running Core2 E4400 Intel processor w/ 4GB of ram ... however, it only recognizes 3.25GB. Nothing I've been able to do enable the system to recognize that last .75GB


Either:

A. You need to enable hardware memory remapping in BIOS
or
B. Your motherboard does not support 4GB+
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Postposted on Sat Dec 22, 2007 1:23 am

Voldenuit wrote:Either:

A. You need to enable hardware memory remapping in BIOS
or
B. Your motherboard does not support 4GB+


How to do "A"? The Motherboard supports 4GB max as per specs of the Mobo itself.
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Postposted on Sat Dec 22, 2007 1:57 am

DigitalN00b wrote:
Voldenuit wrote:Either:

A. You need to enable hardware memory remapping in BIOS
or
B. Your motherboard does not support 4GB+


How to do "A"? The Motherboard supports 4GB max as per specs of the Mobo itself.
What is your motherboard?

There should be a setting in the BIOS called "Memory hole remap" or something like that. It has to be enabled.
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Postposted on Sat Dec 22, 2007 2:47 am

Flying Fox wrote:
DigitalN00b wrote:
Voldenuit wrote:Either:

A. You need to enable hardware memory remapping in BIOS
or
B. Your motherboard does not support 4GB+
How to do "A"? The Motherboard supports 4GB max as per specs of the Mobo itself.
What is your motherboard?
DigitalN00b wrote:Here's one for you all. I'm running Windows XP Professional x64 on a Biostar 945P-A7A 8.0 Motherboard running Core2 E4400 Intel processor w/ 4GB of ram ...
There should be a setting in the BIOS called "Memory hole remap" or something like that. It has to be enabled.
I don't see an option for that in the manual. The updated BIOS might have it, but possibly not In which case, you may be SOL -- technically, the board does support 4GB, but not all of it is accessible. (The BIOS optoin to remap memory was ony available on server boards until fairly recently).
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Postposted on Sat Dec 22, 2007 4:38 am

And to be even more basic, to get into the BIOS, you have to press a button early at boot time (when it shows memory, etc). Most of the time, it's either the DEL or the F2 button, but it depends on the motherboard and what brand of BIOS they've chosen to implement.
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Postposted on Sat Dec 22, 2007 9:19 am

Wait, I thought memory hole remap didn't do any good for a desktop Win32 OS, because they refused to see anything over 4 GiB anyway. :-?

By far the easiest (only?) way to get more than ~3.3 GiB of RAM on a Win32 system is to run Windows Server 2003.
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Postposted on Sat Dec 22, 2007 9:49 am

bhtooefr wrote:Wait, I thought memory hole remap didn't do any good for a desktop Win32 OS, because they refused to see anything over 4 GiB anyway. :-?

By far the easiest (only?) way to get more than ~3.3 GiB of RAM on a Win32 system is to run Windows Server 2003.


DigitalN00b said he is running XP x64 so he shouldn't have to do anything odd with Windows, he just needs to convince his motherboard to do the 3-4GiB memory remap.
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Postposted on Sat Dec 22, 2007 12:28 pm

SuperSpy wrote: ... he just needs to convince his motherboard to do the 3-4GiB memory remap.
The Question now is: How?
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Postposted on Sat Dec 22, 2007 1:17 pm

There should be a setting within your bios that mentions something to that effect. For most motherboards I've seen it's in the memory configuration setting. It usually says something along the lines of:

Memory Remap: Disable/Enable

Though probably not exactly that. If you post some shots of your bios we could help you find it...
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Postposted on Sat Dec 22, 2007 1:22 pm

MaxTheLimit wrote:There should be a setting within your bios that mentions something to that effect. For most motherboards I've seen it's in the memory configuration setting. It usually says something along the lines of:

Memory Remap: Disable/Enable

Though probably not exactly that. If you post some shots of your bios we could help you find it...
I downloaded the manual last night (see link above). As I said in my earlier the post (the one where I repeated N00b's note that he's using x64) I don't see that option in the BIOS manual or in any of the screenshots it includes. Like I said, it <i>might</i> be available in a later BIOS update, but it's also possible the motherboard isn't capable of it (they had to include the additional address lines, and until recently mfrs only bothered with that on "server" boards).

But I encourage you to download the BIOS manaul yourself (PDF) and look; it's possible I missed something.
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Postposted on Sat Dec 22, 2007 1:41 pm

I'm going to do a little research and see if any of the bios updates mention anything about memory remap.

...

EDIT:
While looking through the newest bios update manual I found this:
Image

Would this be what we need? I think so.
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Postposted on Sat Dec 22, 2007 2:30 pm

MaxTheLimit wrote:EDIT:
While looking through the newest bios update manual I found this:
{pic}

Would this be what we need? I think so.
I think not. That actually reserves memory for ISA cards (as the manual mentions in a cryptic fashion), so that would make the problem worse -- in effect "stealing" another 1MB from available memory to make that address range available for a card that he doesn't have and (on a motherboard lacking ISA slots) couldn't install.
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Postposted on Sat Dec 22, 2007 2:39 pm

Hmm, well that's all I seem to be able to find that even remotely seems related. Might just not be an option on the board.
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Postposted on Sat Dec 22, 2007 2:45 pm

MaxTheLimit wrote:Hmm, well that's all I seem to be able to find that even remotely seems related. Might just not be an option on the board.
Yeah, that's what I concluded. Unfortunately. As bitvector said in the first few posts in this thread (and he and others re-iterated later): to see the full 4GB of memory, a 64bit OS is <i>necessary</i> but is not in itself <i>sufficient</i>, because hardware support has to be there on the board itself and the BIOS has to offer the option.
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Postposted on Sat Dec 22, 2007 3:15 pm

The good news is that a mother board that supports it isn't all the expensive...though that on top of the price of the ram, and for a lot of people upgrading their OS.....it starts to add up in costs. I am thankful my board has the option. Some are just not so lucky. A lesson to always plan ahead though I guess.
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Postposted on Wed Dec 26, 2007 2:05 am

Ah, your board is a 945P chipset. That's funny because the first time I became aware of this problem was because of the 945 chipset. It was about a year and a half ago when we bought an Intel-branded 945G board at work and maxed it out with 4GB of RAM. It was running 64-bit Linux and could only see 3.3GB of RAM. We had a bunch of Opterons with 4GB and greater and didn't have that problem, so it was annoying. After poking around (there was a lot less info on this at the time), I pieced together that the 945 chipset just didn't support a larger physical address space so there was no way we could use that memory. It was very frustrating because everyone kept telling me, "oh man, just use 64-bit -- that'll fix everything." From what I understand about the 945's memory controller, unfortunately no BIOS update will bring the remapping feature.*

I remember a coworker of mine was quite angry because the Intel box stated that up to 4GB of memory is supported (when they damn well knew it would be limited).

* If you look at the 945 chipset's memory controller hub datasheet, it says: "the (G)MCH supports 32-bit host addressing, decoding up to 4 GB (2 GB for the 82945PL/82945GC/82945GZ) of the processor's usable memory address space." Contrast that with the P35, which says "supports 36-bit host bus addressing, allowing the processor to access the entire 64 GB of the host address space" or the 975X, which says "the MCH supports 36-bit host addressing, decoding up to 8 GB of the processor's usable memory address space."
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Postposted on Wed Dec 26, 2007 2:31 am

In other words .... change my MoBo. *sighs*
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Postposted on Wed Dec 26, 2007 2:42 am

DigitalN00b wrote:In other words .... change my MoBo. *sighs*

Yeah, unfortunately that seems to be the case :(
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Postposted on Wed Dec 26, 2007 12:59 pm

975X only supports up to 8GB? Dang, does that mean I can only have 6.4GB on my mobo now?
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Postposted on Wed Dec 26, 2007 1:26 pm

Nitrodist wrote:975X only supports up to 8GB? Dang, does that mean I can only have 6.4GB on my mobo now?

That's roughly how I was reading it, too. Which dashes my dreams for an 8GB system. :lol:
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Postposted on Wed Dec 26, 2007 2:51 pm

derFunkenstein wrote:
Nitrodist wrote:975X only supports up to 8GB? Dang, does that mean I can only have 6.4GB on my mobo now?

That's roughly how I was reading it, too. Which dashes my dreams for an 8GB system. :lol:


Huh????? I don't get it. Is this some kind of joke that refers to old "no user needs more then 640KB of memory"?

975X can support 8GB without a problem, the catch is that 2GB DDR2 modules are still very pricey and are not friendly to overclocking.

The problem with 945G is purely a memory controller issue. You got to have a memory controller that can address higher bits in other to take advantage of x86-64 standard greater memory celling. IIRC, the memory controller on K8s are 36-bit = 64GB limit.

I am not sure many bits that memory controller on K10 can address.
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Postposted on Wed Dec 26, 2007 2:55 pm

Krogoth wrote:975X can support 8GB without a problem, the catch is that 2GB DDR2 modules are still very pricey and are not friendly to overclocking.

975X can support up to 8GB of addressable space, which means that (akin to the whole 4GB situation), you may as well have 8GB, but you'll have to reserve memory for the hardware, leaving you with 7-odd GB left. At least that's how I read it.
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Postposted on Wed Dec 26, 2007 3:33 pm

morphine wrote:
Krogoth wrote:975X can support 8GB without a problem, the catch is that 2GB DDR2 modules are still very pricey and are not friendly to overclocking.
975X can support up to 8GB of addressable space, which means that (akin to the whole 4GB situation), you may as well have 8GB, but you'll have to reserve memory for the hardware, leaving you with 7-odd GB left. At least that's how I read it.
No. Once you can remap physical memory around the addresses used by the PCI devices, there's no overlap or conflict between them. If your chipset supports the necessary address lines and remapping, then your 64bit OS will see all of the memory just like it does when you have 4GB. In other words, with 8GB your memory map will look like:
000 - 3GB -- memory (3GB)
3GB - 4GB -- PCI devices
4GB - 9GB -- more memory (the other 5GB)

(That's simplified, of course; the break won't necessarily be exactly at 3GB).

You would only run into a problem if the chipset didn't offer at least 34bits of physical address space (since once you go over 8GB you "spill over" from 33bits). With 36bits of physical address space, you'll only start "losing memory" again when you get to 64GB of memory. And you're going to run into other problems before you get there (like finding DIMMs and slots to put them in).
Krogoth wrote:The problem with 945G is purely a memory controller issue. You got to have a memory controller that can address higher bits in other to take advantage of x86-64 standard greater memory celling. IIRC, the memory controller on K8s are 36-bit = 64GB limit.
Actually, the memory controller in the K8 was documented as being capable of 52bits of physical address, but I don't believe more than 40bits was ever implemented in practice.
I am not sure many bits that memory controller on K10 can address.
It's documented as 48bits; but again, I don't know what is actually implemented -- it may still be 40bits (this is also something that may differ between Phenom and Barcelona).
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Postposted on Wed Dec 26, 2007 4:52 pm

Yeah, later in the Intel document it says the following: "The MCH supports a maximum of 8 GB of DRAM; DRAM memory will Not be accessible above 12 GB." I'd take that to mean that you can, in fact, use the remapping above 8GB (but not anywhere in the 36-bit space).

But, who knows... I see how you could interpret the wording the way morphine did since it's not entirely clear how they are defining terms (and what the key distinction between the P35 and the 975X is since they both support 8GB of memory -- what is the real significance of the extra qualification on the 975X). The exact wording in that section is "decoding up to 8 GB of the processor's usable memory address space." One could take that to mean that the MCH can only deal with an 33-bit wide physical address range coming out of the processor and even though it has a design limit of 36-bits, some of them are wired down/ignored in the current chipset revision. But it seems they really do mean that the 36-bits is real, although there are other limitations on your use of it. It'd be nice if they weren't so vague. And, as always, there may be additional caveats imposed when the chipset is actually integrated into a motherboard.
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Postposted on Wed Dec 26, 2007 6:31 pm

UberGerbil wrote:No. Once you can remap physical memory around the addresses used by the PCI devices, there's no overlap or conflict between them.

My bad. According to what bitvector posted, I had understood that 975X has an 8GB address limitation, not just physical RAM limitation.
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Postposted on Tue Jan 08, 2008 7:25 pm

So how does the math look like? You have a 32-bit virtual address pointing to something that is larger than can be expressed with 32 bits :roll:
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