Author Topic: Max memory for Win XP? (Read 574 times)

jigsaw · « **on:** January 03, 2007, 08:00:09 AM »

Anyone have a definitive answer to whether the max memory for XP is 2 or 4 gigs? All the searches I've done are split on the answer.

Thanks

mipoikel · « **Reply #1 on:** January 03, 2007, 08:55:55 AM »

4gb max.

Rolex · « **Reply #2 on:** January 03, 2007, 09:24:08 AM »

Only 2 GB of that would be directly accessible by applications. The other 2 GB would be only accessible by Windows. That may be the causing the confusion.

Schutt · « **Reply #3 on:** January 03, 2007, 12:02:50 PM »

Unfortunately it is eaven more complicated, i would like to see a comprehensive and complete explanation but i couldnt find one. If anyone has a ressource that helps i would like to know.

How far i got:

Windows XP 32bit supports max of 4GB RAM. There is no way around that, but from now on it gets pretty confusing.

The Intel x86 architecture in its current implementation has various I/O, BIOS and other hardware mapped to the memory range from 3GB to 4GB physical adress. So on a normal pc only the RAM range of 0 - 3GB (something around that, might be 2.8-3.2) can be used since the remaining range is occupied already.

On newer hardware (with PAE) this could be moved to a diffrent range, but as i understand it xp (32bit, lets only talk about that for now) can only access 4GB so i think it can not work if the ressources (or the RAM) is remapped.... however i dont have any verrification for that. Apart from that it depends on the motherboard if that is possible at all (guess it is with M2 and 775 hardware but i dont know?)

Windows XP per default gives one process a maximum adress space of 2GB and a system adress space of 2 GB. But while one process cant have more Memory than 2GB, there could still run other processes which use another 2GB each AND the System uses RAM as well.
There are 2 exeptions:

Win32 programs may use "3G" addressing in which case they may use 3GB while windows system memory gets limited to 1GB, which has the shortcoming that it must be switched on at windows boot time AND the windows system has trouble running in 1GB and runs out of memory.

Apart from that Win32 apps can use AWE, which gives them aditional memory (i.e. address space).

So the conclusion is if you have 3GB of RAM it is used, since windows kernel uses some and the apps use the rest, up to 2GB per app normally. If you put in 4GB with windows XP32 1GB will not be used at all.

With Win64 or other 64 bit operating systems the ram can be remapped and full 4GB can be used.

So what i am now burning to know and probably cant sleep:

Does anyone have sources to see if any current hardware (if the CPU supports PAE) could use 4GB of RAM with a 32bit OS?

Does AH2 somehow use AWE / 3G / PAE ?

ciao schutt

Skuzzy · « **Reply #4 on:** January 03, 2007, 09:01:30 PM »

On PAE, Windows XP does not have support for it. Therefore XP is relegated to a maximum address range to 4GB. Now, how that memory is all used is really anybody's guess. The OS is going to allocate X amount for itself, no matter what.

Microsoft is not going to say, from what I can gather. Even with PAE support, a 32 bit OS can only address a contigous memory block of 4GB. It can support many of those 4GB pages, but 4GB is the maximum contigous amount of memory it can physically support.

MS would have to go through some effort to not support more than 2GB of RAM. It would have been silly. Of course, they do have thier silly moments. Vista anyone?

Or how about Windows ME (Mostly Errors)

jigsaw · « **Reply #5 on:** January 05, 2007, 03:19:27 PM »

Thanks for all the info guys. Made my head hurt a bit, but cleared a lot of things up.

Rolex · « **Reply #6 on:** January 05, 2007, 07:08:09 PM »

Here is a link I should have posted before:
http://www.microsoft.com/whdc/system/platform/server/PAE/PAEmem.mspx

Skuzzy · « **Reply #7 on:** January 05, 2007, 07:24:46 PM »

Hehe, that link is full of contridictions Rolex. They claim XP and 2000 support PAE, but then also claim they only support 4GB of RAM. DOH!

Those silly people.

Rolex · « **Reply #8 on:** January 05, 2007, 08:23:13 PM »

It's all those contradictions that keep IT people in demand.

I wonder if Microsoft people are all snickering when they write up these things...

"Hey guys, look at this I'm going to post." (snicker snicker)

"Hahaha! That's great. It'll confuse them for awhile!"

Skuzzy · « **Reply #9 on:** January 05, 2007, 09:08:37 PM »

Well, it really isn't a contridiction as much as it is a lie. By defination, if you implement PAE, you support more than 4GB of RAM. Without PAE, a 32 bit OS can only address 4GB of RAM.

You have to be careful when reading MS generated documentation. It almost always is a good mix of marketing and technical. The marketing is there to make sure nothing negative gets said by the technical side. While the technical side cannot override marketing's lies.

Schutt · « **Reply #10 on:** January 06, 2007, 08:13:59 AM »

Well i tried to dig a bit deeper into that... so far i got to:

WindowsXP supports 4GB of ram.

Since SP2, when No Execution bit is enabled in windows, windows automatically uses PAE as well. There are other possibilities to switch PAE on, but i dont know which exactly.

Adress space:

Windows usually gives 2GB of adress space for the process and 2GB for the system. I am not a wizzard in directx programing but i would venture a guess that at least part of the memory used by directx is in system space which would give programs using directx give the ability to use some of the system ram for the graphics stuff.

When the /3G switch is given in boot.ini for the entry that currently runs programs may use up to 3G of Adress space, but that prevents them from using more than 16GB with AWE. System adress space is then only 1G which might be a bit short in some cases (i couldnt find in which cases that is short).

When PAE is enabled programs may use more than 2GB RAM by using AWE (Address Window Extention) which is something similar like the old EMM. I have no clue which programs use that except for Microsoft SQL Database and Oracle, for which i found indications that they use it. So WindowsXP uses PAE in to give more more memory to the applications via AWE.

Useable RAM:

When 4GB RAM is installed windows normally uses 2.8-3.4 GB of RAM, the rest is not adressable since PCI,PCIe and other hardware addresses are there. How much is useable depends on the motherboard bios and how it does the mapping.

However i found no real indication if WindowsXP might be able to use PAE and that way has access to all RAM when PAE is enabled. I beleave it doesnt, but i talked to a lot of people about it and some beleave it can, and the "4G makes no sense" derives from times before SP2, where it couldnt.

Anyone got 4GB of RAM in his computer and a processor that supports PAE and has the no execute bit enabled?

ciao schutt

MrRiplEy[H] · « **Reply #11 on:** January 06, 2007, 09:21:22 AM »

The fanbois at hardocp forums say that Vista does not hog memory but only reserves it smartly like linux. They also claim Vista is even faster than XP on games.

Then again when you look at their system specs they have 4Gb low latency ram that probably costs alone as much as a typical gaming box.

Krusty · « **Reply #12 on:** January 06, 2007, 11:39:41 AM »

So, in other words, they're spending a small FORTUNE on a kick-arse SUPER high-end system.... just to get exactly the same performance we have today on our current boxes....

llama · « **Reply #13 on:** January 06, 2007, 12:49:20 PM »

Quote

Originally posted by MrRiplEy[H]
The fanbois at hardocp forums say that Vista does not hog memory but only reserves it smartly like linux. They also claim Vista is even faster than XP on games.

Then again when you look at their system specs they have 4Gb low latency ram that probably costs alone as much as a typical gaming box.

I have posted some Vista versus XP benchmarks here on this forum at:

http://forums.hitechcreations.com/forums/showthread.php?s=&postid=2289060#post2289060

Thus far, in terms of 3dMark, XP is faster than Vista, but not by as much as I thought it would be.

These results are on what I would most definately call a "typical" gaming box, if not one that's now a little weak by today's standards...

-Llama

MrRiplEy[H] · « **Reply #14 on:** January 06, 2007, 01:07:09 PM »

Unfortunately synthetic benchmarks tell nothing about real world playability.