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Index > Heap > windows limited (xp,7,8)32 bit hack PAE, break 4GB ram limit

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sleepsleep



Joined: 05 Oct 2006
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sleepsleep
i actually believe 32 bit machine are limited to only 4GB memory,

then i read about absurd microsoft licensing to hard limit 32bit OS to only 4GB memory even with PAE switch.

the truth is, using PAE in linux, a 32bit OS could actually gone up to 64GB memory

so, maybe all should just stay in 32 bit, there are still lots of room here!

i gonna try XP PRO with 8GB today.
wonder anyone could point me a bios mod to disable acer 471G nvidia optimus, damn it acer.

http://www.geoffchappell.com/notes/windows/license/memory.htm
Quote:
Geoff Chappell, Software Analyst

You are at the home page of a website that has grown out of an academic interest in studying what software actually does, which is much too often not exactly what the manufacturer says the software does. Pretty much everything here has been obtained by reverse engineering other people’s computer software, not so that their ideas can be stolen and reworked, but so the actual working of what they sell can be understood and reported.

The software examined here is almost always either Microsoft Windows or one of Microsoft’s programming tools for Windows. Very little of what I write about this software is intended for a general readership. If anything, most is at the other extreme: I take as granted that you have a sound understanding of advanced Windows programming in general and a good knowledge of what Microsoft has already documented of the particular topic. Where something I write conflicts with Microsoft’s documentation, my aim is that you should be able to rely on me to be correct and Microsoft to be mistaken, because Microsoft at best documents what its programmers thought they coded into the software but I document what actually is there.

There are nearly 2,000 pages here. Some are merely placeholders for work that never properly got under way or for introductions that I probably never will get round to writing. Some just track what’s new or was new. Others are statistics about what gets viewed. But the overwhelming bulk of pages here exist to say something original—not necessarily important but original nonetheless. This is not one of those many websites that collate suppositions from who knows where on the Internet. Though I may slip up now and then, my intention is that all the substantive work at this site is original research into primary sources, unless another source is noted, or is the application of that research to comment on a primary or secondary source. Let it be stressed: the only primary source in a study of computer software is the software—not the product documentation, not even the source code, just the software as actually executed by the computer.

For more about the nature of this work and my reasons for doing it, please read Software Analysis by Reverse Engineering.

great site with lots of info!!
Post 18 Jun 2014, 07:17
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sleepsleep



Joined: 05 Oct 2006
Posts: 8904
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sleepsleep
below are information to perform hack on pae limit.

http://iknowu.dnsalias.com/files/public/Windows_XP_SP3_Remove_PAE_Limit/Windows_XP_Remove_PAE_Limit.htm

http://alturl.com/7dpyt

Quote:
Windows XP SP3 - Remove the 4GB physical address / RAM limit and use up to 64GB RAM using PAE

The limits of 32-bit memory addressing were addressed back in 1995, and a technology called PAE was developed, in order to extend the addressable memory to 36-bit (64GB).
PAE capable OS can address up to 64GB of RAM (note: each process can still only address 4GB)


chinese language information
http://bbs.pediy.com/showthread.php?t=142776

glad to find these great information!!
Post 18 Jun 2014, 08:38
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Feryno



Joined: 23 Mar 2005
Posts: 454
Location: Czech republic, Slovak republic
Feryno
32 bit OS running with PAE=1 is capable to use more than 4GB of RAM but virtual address space is still limited to 4 GB.
Post 18 Jun 2014, 09:37
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sid123



Joined: 30 Jul 2013
Posts: 340
Location: Asia, Singapore
sid123
Actually I've researched previously and it's possible to use > 4GB RAM even without PAE under an AMD processor! The processor has an interesting MSR (Model Specific Register) called WRAP32DIS which as it says disables the 32-bit address wrap. So you could technically use 8GB of RAM by using different segment registers (FS/GS). Not many people know about this but it is revealed in the AMD BIOS and Kernel developers guide.

PAE (Physical Address Extension) as the name says is another form of paging, Sadly PAE also wastes a lot of memory than conventional page tables. Each address is stretched from 32-bits to 64-bit in the page table. However the memory gained using PAE is much more than without PAE. Smile

All 64-bit OSes also use PAE, but with PML4 (Page Map Level 4) and can access upto 2^52 memory units. Smile Sadly we're running out of physical capabilities of the motherboard. So not sure if we can have that much RAM one day. Wink

edit: btw this is going to be like "No one needs more than 640K" but I don't think we are ever going to need more than 2^52 memory units (bytes).
Post 18 Jun 2014, 10:11
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17287
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revolution
sid123 wrote:
edit: btw this is going to be like "No one needs more than 640K" ...
Well the first statement is true: No one needs more than 640K. But what we want and what we need are two different things.
sid123 wrote:
... but I don't think we are ever going to need more than 2^52 memory units (bytes).
Famous last words. Some tasks that run today already need more than that. The Internet archive uses more than that.
Post 18 Jun 2014, 10:40
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Coty



Joined: 17 May 2010
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Coty
Yeah... I need more ram, my cpus cache has more than 640k. Why? Think about hospitals, like cat scans, large amounts of memory allow doctors to process large image files accurately quickly and allow them to view in large scale (zoom in) at the point that you'd need to print a billboard to see all of the details. You could go on with medicine and whether tracking. 640k just isn't enough.

Saying we don'ts need more than 640k is like saying we don't need to help people with cancer.
Post 19 Jun 2014, 21:22
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
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Location: In your JS exploiting you and your system
revolution
Coty wrote:
Saying we don'ts need more than 640k is like saying we don't need to help people with cancer.
We don't need to help people with cancer. This is also true. We don't even need to have computers. Anyhow I think you are conflating want and need.
Post 19 Jun 2014, 22:58
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sleepsleep



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sleepsleep
Feryno wrote:
32 bit OS running with PAE=1 is capable to use more than 4GB of RAM but virtual address space is still limited to 4 GB.


imo, it is reasonable to run consumer pc program in under 4 GB limit.
Post 20 Jun 2014, 06:09
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sleepsleep



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sleepsleep
sid123 wrote:

All 64-bit OSes also use PAE, but with PML4 (Page Map Level 4) and can access upto 2^52 memory units.

so, could OS use PML4 in 32bit mode?
Post 20 Jun 2014, 06:11
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HaHaAnonymous



Joined: 02 Dec 2012
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HaHaAnonymous
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Last edited by HaHaAnonymous on 28 Feb 2015, 18:10; edited 1 time in total
Post 20 Jun 2014, 14:34
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sleepsleep



Joined: 05 Oct 2006
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sleepsleep
someone coded a patch for PAE 4GB memory limit,
with source code =) and this is really cool, if i could translate it to fasm version,

http://wj32.org/wp/2011/02/23/pae-patch-updated-for-windows-7-sp1/

gonna try his patch =)
Post 01 Jul 2014, 04:34
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