P5B & 4GB Memory - Question

[PeterT]

I had 2 x 1GB in the board and as expected, it showed 2048MB in the BIOS and in memtest. I put another 2 x 1GB in and instead of showing 4096MB the BIOS and memtest, it shows 3008MB and 3007MB, respectively. What gives?

I know I won't be able to utilize the whole 4GB in a 32 bit OS, but shouldn't it be visible/usable in the BIOS and memtest.

edit: I tried re-seating all 4 sticks. Also confirmed that it shows 2048 if I use 2 x 1GB in either the black or yellow slots independently.

help.

[CrowdAds]

[PeterT]

I found an option on the Northbridge page in the BIOS called "Memory Remap Feature". Default is disabled. I changed it to enabled and now it shows 4096MB. Is that it?

[SRTDodge05]

All the info you need right here.
The system memory that is reported in the System Information dialog box in Windows Vista is less than you expect if 4 GB of RAM is installed

[PeterT]

Thanks SRT. Yep, that was it: "The BIOS must support the memory remapping feature. The memory remapping feature allows for the segment of system memory that was previously overwritten by the Peripheral Component Interconnect (PCI) configuration space to be remapped above the 4 GB address line. This feature must be enabled in the BIOS configuration utility on the computer."

[PeterT]

I am planning on running XP Pro 32 bit. Do I have to disable the "Memory Remap Feature" to run a 32 bit OS?
TIA

[SRTDodge05]

I dont see why you would have to, i would leave it enabled and installed xp.

[PeterT]

cool. will give it a shot. thx.

[PeterT]

OK... I need some more help with XP and 4GB.

With the memory remap feature enabled in BIOS, the XP system properties box shows 2GB.
With the memory remap feature DISabled in BIOS, the XP system properties box shows 2.93GB.

I tried the "3GB switch" detailed here, but see no difference:
Memory Support and Windows Operating Systems

Is it possible to get XP 32-bit to see and use all 4GB? How?

I put Vista 64-bit on it to see if it would see and use all 4GB and it did, but I can't use that OS b/c it is an RC1 evaluation copy.
And, I don't want to spend $190 on Vista Ultimate 64-bit any time soon.

Tried google, lots of hits, but no joy.
TIA for any insight.

[PeterT]

Found this:
The amount of RAM reported by the System Properties dialog box and the System Information tool is less than you expect after you install Windows XP Service Pack 2
It sheds some light on the subject, but doesn't answer my question, which is twofold:
1. How should I configure the BIOS and OS to be sure that the OS and apps can use all 4GBs? (I do not have the /PAE switch in the boot.ini, but it does show PAE in the system properties box.)
2. Is it impossible to get XP SP2 to display all 4GB? (I think the answer to this no.)
TIA.

[shaihulud]

A BIOS option that is not necessary, or does not fit the context, should never be enabled. Disabled the remapping bit when using an operating system that is only 32bits. As for you being able to use “all” of the 4GB when in 32bit mode, you are not paying close enough attention, and unfortunately the semantics of it all exacerbates it.

ALL of the memory is in use by Windows. However, since everything resides in memory, what is mapped to a device cannot be in use by an application at the same time (it will crash). This is why the PCI hole cannot be used as system memory. So Windows, Linux, UNIX, all of the operating systems capable of 32bits use all of the 4GB. You are not losing any memory and will not be able to make any changes unless you chose to use a 64bit operating system and enable 64bit processing and memory management.

Do not make any other changes, leave the system as be. What you mainly read on the Internet concerning this matter is very much so incorrect. This is concerning PAE and the switches. Matter of fact you are most likely in PAE already, if you have a recent modern processer and SP2 for Windows XP.

[PeterT]

Thanks for the reply shaihulud. I am trying to determine the correct settings to use in the BIOS and Windows and appreciate the help.

So, I should:

1. DISable the "Memory Remap Feature" in the BIOS (when I do this, the total memory reported is: 3008MB in BIOS and 2.93GB in Windows)
2. Remove the "/3GB" switch from the boot.ini

Correct?

[k0NG0]

Originally Posted by shaihulud

A BIOS option that is not necessary, or does not fit the context, should never be enabled. Disabled the remapping bit when using an operating system that is only 32bits. As for you being able to use “all” of the 4GB when in 32bit mode, you are not paying close enough attention, and unfortunately the semantics of it all exacerbates it.

ALL of the memory is in use by Windows. However, since everything resides in memory, what is mapped to a device cannot be in use by an application at the same time (it will crash). This is why the PCI hole cannot be used as system memory. So Windows, Linux, UNIX, all of the operating systems capable of 32bits use all of the 4GB. You are not losing any memory and will not be able to make any changes unless you chose to use a 64bit operating system and enable 64bit processing and memory management.

Do not make any other changes, leave the system as be. What you mainly read on the Internet concerning this matter is very much so incorrect. This is concerning PAE and the switches. Matter of fact you are most likely in PAE already, if you have a recent modern processer and SP2 for Windows XP.

Nit: it's using all of the address space, not all of the memory.

[TQ]

It's threads like this that make me love this place...

[SRTDodge05]

Ive seen 32bit os show the full 4gb in windows, doesnt mean it will use the full 4gb but atleast you know its there.

[shaihulud]

Incorrect, memory is all address space (its logical partitioning). 4GB starts from 0x0000000 and the boundary is 0xFFFFFFFF. Mapped devices are within their boundary of this 4GB range, accordingly, when in 32bit mode. To say Windows is not using all the RAM is very much so incorrect. The mapped PCI I/O space has been addressed by the manager and the driver has reserved the area(s) for the activities within memory. Because of this, mapped I/O cannot be allocated as free physical or system usable memory.

Most think that since it cannot be allocated, or is not “seen”, et al, that Windows cannot use it. When the very space is and always has been in use.

1. DISable the "Memory Remap Feature" in the BIOS (when I do this, the total memory reported is: 3008MB in BIOS and 2.93GB in Windows)
2. Remove the "/3GB" switch from the boot.ini

Correct?

I would advise, to do as so.