32bit OS Ram limitation

ctasker

Hi
Am putting a spec together for a graphics/modelling PC
Some of the work i do pushes my current machine with 1Gb SDDDR to the wall so i'm keen to put as much ram in my new system as the OS will make available.

While the motherboards i've been looking at support a maximum of 4GB i gather that Windows XP will not allow your applications to utilise a significant amount of this, can anyone who has an understanding of RAM usage tell me how much i can make available.
The new machine will have a Athlon64 x2 4400 processor
Mainboard will be PCI express SLI ready
I normally need to run about 3 apps concurrently including Max, photoshop and ACAD so this is part of my problem and why ram is as critical.
Any info would be appreciated

SouperComputer

im speaking off teh cuff here, but the limitation of the boards is possibly to do with current RAM density.

ATM we only have 1Gb modules. So four slots naturally is 4GB. Depending on what board you get, it should support higher densitys whereby we have 2GB and 3GB a stick and so on, but the modules aind around yet.

Another angle: It's not cost effectve for manufacturers to pack 2Gb of BGA RAM at current densities on a single module. This is probably what would be needed to make 2GB RAM sticks to work with a wide range of boards, without BIOS upgrades etc.

I think if you go for any board worth its salt, it will support 8GB RAM with ease when the modules come on the market. All you can do is get a board with as many slots as possible and cross your fingers!!

sceptre

ctasker wrote:

While the motherboards i've been looking at support a maximum of 4GB i gather that Windows XP will not allow your applications to utilise a significant amount of this, can anyone who has an understanding of RAM usage tell me how much i can make available.

Well, it's 32 bits so it supports 4GB of memory (2^32). The enterprise edition and datacentre edition of win server 2003 support up to 32GB and 64Gb respectively (I assume using PAE, though I don't care enough to know).

However your understanding is correct. 2GB is for applications and 2GB is only available to the windows kernel and exec software as a flat address space. Having said that, the amount available to applications can be expanded to 3GB if there's a /3GB switch used in the boot.ini file. That extra memory is only available to applications that have a specific header in their executable file so it knows how to use it.

On a simple basis, of your 4GB, the apps get only up to 2 and windows reserves the other 2 for itself.

Capt'n Midnight

http://www.microsoft.com/whdc/system/platform/server/PAE/PAEmem.mspx

Operating systems based on Microsoft® Windows NT® technologies have always provided applications with a flat 32-bit virtual address space that describes 4 gigabytes (GB) of virtual memory. The address space is usually split so that 2 GB of address space is directly accessible to the application and the other 2 GB is only accessible to the Windows executive software.
..
Windows XP Professional and Windows Server 2003 Memory Support. The maximum amount of memory that can be supported on Windows XP Professional and Windows Server 2003 is also 4 GB. However, Windows Server 2003, Enterprise Edition supports 32 GB of physical RAM and Windows Server 2003, Datacenter Edition supports 64 GB of physical RAM using the PAE feature.

The /3GB switch allocates 3 GB of virtual address space to an application that uses IMAGE_FILE_LARGE_ADDRESS_AWARE in the process header. This switch allows applications to address 1 GB of additional virtual address space above 2 GB.

So in order to see more ram all you need to do is buy a much more expensive license
The /3GB switch allocates 3 GB of virtual address space to an application that uses


Windows XP SP1 May Not Start with the /3GB or /USERVA Switch
http://support.microsoft.com/default.aspx?scid=kb;en-us;328269

you may also want to look up the i-ram put a 4GB swap file on it

ctasker

Thanks for the info guys,
Do you know if the IMAGE_FILE_LARGE_ADDRESS_AWARE in the process header is something that you have to (or can) change yourself or if it is a feature that needs to already be in the application before you have the option of using more than 2GB?
Also the i-ram you mentioned, are you referring to allocating 4GB of space for the hard disk swap file or is this something else?

I will be getting XP professional on the new machine can't imagine that any of the other OSs mentioned would be a viable option for me or even what kind of hardware you would fit that much ram into 64GB! phew

Laguna

AFAIK, 32-bit Windows XP can only address 4gb of RAM, hence the motherboards limitation.

pdogs

Physical Address Extension. PAE is an Intel-provided memory address extension that enables support of up to 64 GB of physical memory for applications running on most 32-bit (IA-32) Intel Pentium Pro and later platforms. Support for PAE is provided under Windows 2000 and 32-bit versions of Windows XP and Windows Server 2003. 64-bit versions of Windows do not support PAE.

Also taken from Memory Support and Windows Operating Systems

theexis

Would it be an option to consider going 64bit if this is a new system - even if 64 bit application software isn't available, 32 bit /3 GB aware apps get the full 4GB of RAM for themselves (assuming you have the hardware of course!).

Capt'n Midnight

theexis wrote:

Would it be an option to consider going 64bit if this is a new system - even if 64 bit application software isn't available, 32 bit /3 GB aware apps get the full 4GB of RAM for themselves (assuming you have the hardware of course!).

Well the limit is artificial since the windows enterprise / dataserver can see more, so have a look at the microsoft site to see what they allow you to use with the 64 bit version.

Mutor_CS

You're all confusing physical and virtual memory here.
XP as a 32-bit OS can address up to 4GB of physical memory. Putting 4GB of RAM in your system will give you a performance benefit, although the leap from 1GB->2GB is probably more noticeable than 3GB->4GB.

The 2GB/3GB user address space banter above occurs for any amount of physical memory. Each process in XP gets to 'see' 4GB of virtual space when it runs. The /3GB switch alters the system that only 1GB of that virtual 4GB is reserved for kernel use.

ctasker: You have 1GB now, so any increase will help you.
4GB is a good idea if the motherboard is stable with that amount of RAM and you are running more than one memory hungry process (and you are).