Maximum Memory Clarification

[harrillj]

Greetings,
I have read various explanations regarding the maximum installed memory on Windows XP, but some appear to be conflicting each other. There are many motherboards that accept 4GB of ram now, but at the same time I have read that applications will only use 2GB of the 4GB. So... does installing 4GB smply a waste of money?

Intel has just announced their 64-bit Xeon 3.60 800 MHz FSB processors, for which Dell is now selling a workstation utilizing these processors with options for up to 8GB of ram. Does the 64-bit architecture allow the utilization of 8GB, but the 32-bit does not?

Let me stop rambling... I guess what I am asking if for a clear understanding of how much memory I can install for Windows XP Pro using 32-bit and 64-bit architectures. Any feedback is appreciated.

Thanks in advance.
Jim

 

[MrChad]

Windows XP (32-bit) supports up to 4 GB of RAM and is limited to 2 GB per individual process (I believe).

Windows XP (64-bit) supports up to 16 GB of RAM. I'm not sure about the per-process limit. Of course, you'll need native 64-bit software in order to utilize the extra addressible space.

 

[Nothinman]

Each process on a 32-bit system is limited to 2G of VM (parts of which are taken up by the executable, shared library mappings, etc). If you boot Windows with the /3G switch it'll increase that limit to 3G but the OS has to be told that each executable is allowed to have that 3G, by default it's still a 2G/2G split even with the /3G switch. The OS can use up to 64G with hacks like PAE if you pay for the really expensive versions of Windows, but apps will be limited.

The per-process limits on a 64-bit system is in the terrabytes I believe, maybe higher. But for it to matter at all you need a working 64-bit OS (and for Windows, 64-bit drivers are still pretty rare) and a 64-bit executable for the app otherwise it'll be run in compatibility mode. But, atleast on AMD64, the compatibility mode allows each process to access all 4G of the 32-bit VM since the kernel space is in another section of the VM.

 

[imported_Phil]

Originally posted by: Nothinman
Each process on a 32-bit system is limited to 2G of VM (parts of which are taken up by the executable, shared library mappings, etc). If you boot Windows with the /3G switch it'll increase that limit to 3G but the OS has to be told that each executable is allowed to have that 3G, by default it's still a 2G/2G split even with the /3G switch. The OS can use up to 64G with hacks like PAE if you pay for the really expensive versions of Windows, but apps will be limited.

The per-process limits on a 64-bit system is in the terrabytes I believe, maybe higher. But for it to matter at all you need a working 64-bit OS (and for Windows, 64-bit drivers are still pretty rare) and a 64-bit executable for the app otherwise it'll be run in compatibility mode. But, atleast on AMD64, the compatibility mode allows each process to access all 4G of the 32-bit VM since the kernel space is in another section of the VM.

That info should really go in the FAQs, excellent explanation

 

[harrillj]

So, if I didn't want to "play" with switches and the OS for the 3 GB split, is it fair, or logical, to simply sit tight until Windows 64 bit OS is common place (whenever that will be), and..... that my specific application (in this case Adobe Photoshop CS) is updated to utilize the 64-bit OS (whenever that will be)??

 

[Nothinman]

64-bit OSes are common, just not Windows. Just about every unix has been 64-bit clean for atleast a decade, but since you need an Adobe product that really doesn't help you much. Depending on what your needs are you could try 64-bit Linux on an Opteron and run the GIMP and/or ImageMagick which would be 64-bit.

 

[NewBlackDak]

I can't imagine the image manipulation in Photoshop that needs 4GB of Ram.

 

[dawks]

Originally posted by: NewBlackDak
I can't imagine the image manipulation in Photoshop that needs 4GB of Ram.

You havent spent much time working with Photoshop in the professional graphics industry have you?

I remember Steve Jobs showed a 'benchmark' where they opened a relativly simple Finding Nemo poster that weighed in at 350meg compressed psd. Opened up, that file could easily take over a gig. After working on it for a few hours..... with a 100 levels of un-do's and such...

 

[harrillj]

Although not my profession, I live in Photoshop almost daily, and it is not unusual to have 400 to 500MB files. Each layer adds mucho MBs, as layers is the power of Photoshop. Scanning is even more MB hungry, as I typically scan in 1200 DPI which creates a file that takes 20 seconds to save. I also have a large format printer which can print very large prints and when you get to a high resolution 19 x 13 file, the printing process loves memory. I have 2 GB DDR400 now and have pretty good performance, but with 2 open dimm slots, it would have been an easy decsion for me to add another 2 GB.

 

[Cuular]

Currently the 32Bit windows is limited to a 4GB address space.

So even with 4GB of ram installed, when you check windows for the amount of memory you have, it shows around 3.3GB. Windows needs part of that address space for working in.

So you can't use the full 4GB anyway.

And if you specify a pagefile bigger than 1024MB it will start to eat away at the amount of ram windows thinks it has as well, when you have 4GB installed.

 

[Nothinman]

So even with 4GB of ram installed, when you check windows for the amount of memory you have, it shows around 3.3GB. Windows needs part of that address space for working in.

Actually that's reserved for the PCI address space IIRC, Windows should always show the total amount of physical memory no matter how much is being used by the kernel currrently. And the available physical memory is irrelevant, 4G of VM is available no matter what and 2G of that address space is reserved for the kernel.

And if you specify a pagefile bigger than 1024MB it will start to eat away at the amount of ram windows thinks it has as well, when you have 4GB installed.

I would love to see where you got that idea from.

 

[NewBlackDak]

No, I just work for a Newspaper with the largest commercial printshop in the region.