Have your 32-bit Windows Vista support more than 4GB of RAM.

[Watcher]

You’re probably wondering why I picked a number as horrible as 3.5GB? Why not 4GB? Well, there’s a really technical explanation for this but to make a long explanation short, 32-bit operating systems can only handle up to 4GB of memory. Along with the RAM, you also have other memory-mapped devices such as your video cards. The memory used counts towards the 4GB virtual memory address capacity of a 32-bit operating system. But actually, the world does not end at 4,096 megabytes for 32-bit Windows Vista users anymore because the Arsgeek is here to save the day.

If you’ve accidentally bought 4GB of RAM, this may be a good idea. And I say may because many 32-bit operating systems begin to lose efficiency as they surpass the 4GB mark. For that reason, if you have less than 3GB RAM, it’s not necessarily the best idea to go out and buy some more RAM. If you want to utilize more RAM (between 8GB and 128GB), you can always switch to 64-bit Windows Vista. Alright, enough babbling. Let’s get started.

Steps:

1) Access cmd: Click on the Start Pearl > type cmd in the Search Bar > and press Ctrl + Shift + Enter (this allows you to run cmd in administrative mode)

2) Type BCDEdit /set PAE forceenable

“BCDEdit is a boot configuration editor for the command line. Using the above command you’ve just enabled Physical Address Extension (PAE) which can address memory larger than 4 GB. ” - Arsgeek

http://vistarewired.com/2007/03/29/h...windows-vista/

Watcher

[darknight909]

Im pretty sure its physically impossible for a 32-bit system to handle that much ram

[Darkoz]

Originally Posted by darknight909

Im pretty sure its physically impossible for a 32-bit system to handle that much ram

Yep, that is definitely the case.

[waway625]

well, somebody should try it any volunteers?

[darknight909]

Originally Posted by Darkoz

Yep, that is definitely the case.

OK good, I was hoping I was being an idiot.

Yeah changing a simple registry entry isn't going to make you magically obtain that extra ram

I don't think microsoft and linux and mac os would ALL be hiding the secret registry entry that magically enables 4gb of ram and was never found until Vista was released

[Animatrix]

PAE is nothing new. Not sure why ForceEnable is used without explaining it.

The "pae ForceEnable" switch is used to keep PAE on when disabling hardware-enforced DEP.

http://msdn2.microsoft.com/en-us/library/aa906211.aspx

On a computer that supports hardware-enabled Data Execution Prevention (DEP) and is running a 32-bit version of the Windows operating system that supports DEP, PAE is automatically enabled when DEP is enabled and, on all 32-bit versions of the Windows operating system, except Windows Server 2003 with SP1, PAE is disabled when you disable DEP. To enable PAE when DEP is disabled, you must enable PAE explicitly, by using /set nx AlwaysOff and /set pae ForceEnable.

All CPU's that support and run hardware-enforced DEP have PAE enabled by default, this is implied by the /NOEXECUTE switch.

Physical Address Extension - PAE Memory and Windows
http://www.microsoft.com/whdc/system...AE/PAEdrv.mspx

The PAE kernel can be enabled automatically without the /PAE switch present in the boot entry if the system has DEP enabled (/NOEXECUTE switch is present) or the system processor supports hardware-enforced DEP. Presence of the /NOEXECUTE switch on a system with a processor that supports hardware-enforced DEP implies the /PAE switch. If the system processor is capable of hardware-enforced DEP and the /NOEXECUTE switch is not present in the boot entry, Windows assumes /NOEXECUTE=optin by default and enables PAE mode. For more information, see the topic "Boot Options in a Boot.ini File" in the Windows DDK.

So if your disabling DEP then you can use "/set pae ForceEnable" to keep PAE on, but if your not running a CPU that supports hardware-enforced DEP, and you want to enable PAE you would still need to set the "/PAE" switch to use it. Not sure if the ForceEnable part of the command "/set pae ForceEnable" is just ignored and it ends up as "/set pae".


PAE is part of a larger story which i won't go into but surfeit to say it's not just about adding a switch.

PAE X86 Technical Reference
http://technet2.microsoft.com/Window....mspx?mfr=true
http://technet2.microsoft.com/Window....mspx?mfr=true
http://en.wikipedia.org/wiki/Physical_Address_Extension

Address Windowing Extensions
http://msdn2.microsoft.com/en-us/library/aa366527.aspx

Boot Parameters to Configure DEP and PAE
http://msdn2.microsoft.com/en-us/library/aa468629.aspx


Here are some copy past information:

1. Normal 32-bit virtual 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. Using the /3GB boot switch (also called "4-gigabyte tuning (4GT)") give a 3-GB flat virtual address space, with the kernel and executive components using only 1 GB, giving applications more of the virtual address space.

2. Application Memory Tuning. This capability allows memory-intensive applications to utilize up to 50 percent more virtual memory on Intel-based computers. Application memory tuning provides more of the computer's virtual memory to applications by providing less virtual memory to the operating system.

3. Application Changes. No APIs are required to support application memory tuning. However, it would be ineffective to automatically provide every application with a 3-GB address space.

Executables that can use the 3-GB address space are required to have the bit IMAGE_FILE_LARGE_ADDRESS_AWARE set in their image header. If you are the developer of the executable, you can specify a linker flag (/LARGEADDRESSAWARE).

To set this bit, you must use Microsoft Visual Studio Version 6.0 or later and the Editbin.exe utility, which has the ability to modify the image header (/LARGEADDRESSAWARE) flag. For more information on setting this flag, see the Microsoft Visual Studio documentation.

Some manufacturers preconfigure their applications to use application memory tuning, making it unnecessary for you to make this change. For more information, see your application documentation and contact your application vendor to determine whether they support Large Address Awareness or whether you can enable it in their application.

4. Application Windowing Extensions (AWE). AWE is an application programming interface (API) set that complements PAE X86. AWE is a set of APIs that allows software developers to create applications that use up to 64 GB of physical non-paged memory in a 32-bit virtual address space on 32-bit platforms. This technology allows for windowed views to this physical memory from within the application’s virtual address space.

5. 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.

PAE allows the most recent IA-32 processors to expand the number of bits that can be used to address physical memory from 32 bits to 36 bits through support in the host operating system for applications using the Address Windowing Extensions (AWE) application programming interface (API). For information about the AWE API, see the Base Services section of the Platform SDK.

[Watcher]

I would like to see someone that has 4 GB of memory and running a couple of 512 MB cards in SLI mode to see what memory is available to the system and what influence it has on the OS performance?


Watcher

[Animatrix]

Just so it's clear. Care should be taking when enabling PAE on 32-bit systems as it can cause issues with drivers in particular. In fact as far as i can tell, don't have the system to test any of this, all non enterprise versions of 32-bit windows after SP2 do not support the full use of 4GB RAM, this includes Vista 32-bit (see post and links below). This was done for driver stability.

Who ate my memory?


The consumer versions of 32-bit Windows XP and Vista have a stated limit of 4 GB RAM, but a practical limit of about 3.1 GB. A lot of partial explanations have been floating around, so I thought I would try my hand at clearing up the issue. (Wish me luck!)

The design of the Intel 386 architecture supported access to up to 4 GB of physical memory (32-bit physical addresses) and unlimited virtual memory (4 GB at a time via 32-bit virtual addresses). 4 GB of physical memory seemed quite unthinkable at the time the chip was released, so the actual CPU did not have enough address pins to actually do this. Back then a 32-bit address space seemed extravagant for anything less than a supercomputer or mainframe. Nowadays, you can get 4 GB for under $400, and what was unthinkable in 1986 is within reach of anybody thinking about a new computer.

So at least I can access 4 GB, right? Nope.

The original IBM PC’s processor could access 1024 KB of physical address space, but you could only use 640 KB for RAM. The remaining 384 KB of address space was reserved for memory-mapped hardware and ROM. A similar situation exists with current systems: hardware reserves large chunks of the upper 1 GB of physical address space. Because of these reserved areas, a system with a 32-bit physical address space will be limited to somewhere around 3.1-3.5 GB of RAM.

To overcome the 32-bit limitation, recent x86 CPUs (Pentium Pro and later) have 36 address pins and can address 64 GB of RAM. The original design of the x86 32-bit protected mode only provided access to 32-bit addresses, so PAE (Physical Address Extensions) mode was created to allow access to 36-bit addresses.

PAE mode changes the layout of the page tables. Page tables map virtual addresses to physical addresses. Without PAE, the 32-bit virtual addresses map through 2 levels of page tables (1 level for huge pages) and are translated to 32-bit physical addresses. With PAE, the 32-bit virtual addresses map through 3 levels of page tables (2 levels for huge pages) and are translated to 64-bit physical addresses.

PAE doesn’t do anything to the virtual memory limit. Pointers are still 32 bits, so a process can only access 4 GB of address space at a time. However, using PAE, two or more processes could each access a different 4 GB of physical memory. With proper operating system support (i.e. AWE on Windows operating systems) PAE also allows a process to allocate additional memory outside its normal address space, then swap portions of that additional memory into its address space as needed.

So PAE is the answer, right? Well, maybe…

One thing that can prevent access to more than 4 GB of RAM is motherboard design. PAE can only access 64 GB of memory if all 36 address pins are properly wired up on the motherboard. This is not always the case, since those extra 4 wires make the motherboard just a little bit more expensive to design and manufacture (and use just a little bit more power). Many motherboards (especially on laptops) only have 32 address pins connected. If that is the case, no OS will be able to access more than 4 GB of address space.

Another hardware limitation is the ability of the chipset to remap RAM. If you have 4 GB of RAM, and 600 MB of address space is used up by PCI/AGP reserved areas, the only way to access the top 600 MB of RAM is to remap it into the addresses above the 4 GB boundary. Not all chipsets are able to do this, so some systems will just waste any RAM that happens to be shadowed by a PCI/AGP reserved region.

My BIOS reports 4 (or more) GB of RAM, I’ve enabled PAE, and I still only see 3.1 GB. What gives?

Unless you’re running one of the advanced server varieties of Windows, you won’t see more than 4 GB of physical memory. This is a limitation of Windows designed (I assume) to encourage people building expensive servers to pay more for Windows than those who are using it for normal day-to-day activities.

As for that last 0.9 GB, it all comes down to drivers and system stability. Not all drivers behave well in the presence of 64 bit physical addresses. Many driver authors assume that only the bottom 32 bits of the physical address are valid. Others don't properly handle the creation of bounce buffers when necessary (they’re needed when transferring data from a hardware device to/from a buffer that is above the 4 GB mark in physical memory).

Windows XP originally supported a full 4 GB of RAM. You would be limited to 3.1-3.5 GB without PAE, but if you enabled PAE on a 4 GB system with proper chipset and motherboard support, you would have access to the full 4 GB. As more people began to take advantage of this feature using commodity (read: cheapest product with the features I want) hardware, Microsoft noticed a new source of crashes and blue screens. These were traced to drivers failing to correctly handle 64-bit physical addresses. A decision was made to improve system stability at a cost of possibly wasting memory. XP SP2 introduced a change such that only the bottom 32 bits of physical memory will ever be used, even if that means some memory will not be used. (This is also the case with 32-bit editions of Vista.) While this is annoying to those who want that little bit of extra oomph, and while I would have liked a way to re-enable the memory “at my own risk”, this is probably the right decision for 99.9% of the general population of Windows users (and probably saves Dell millions in support costs). See the relevant KB article and a TechNet article for details.

Some of the server Operating Systems still allow the use of larger amounts of memory. I’m guessing that this is done with the assumption that higher quality parts will be used and drivers will be more likely to have been tested in PAE mode with large addresses.

Side-note: PAE is also related to page execution protection, called "hardware DEP" (Microsoft term), "NX" (AMD term), and "XD" (Intel term). In 32-bit x86 processors, this can only be used in PAE mode. This is why you might see PAE mode used even on systems with less than 4 GB of memory.

Performance note: 3-level page table lookups are inherently slower than 2-level page table lookups. However, the processor has substantial dedicated circuitry that usually eliminates most of the performance impact.

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

[Watcher]

Hello Animatrix:

Well, that answers my question. Thank You.

Too bad that it really has no use in the real world.

Watcher

[Animatrix]

Yes, if you want to run 4GB or more get a 64-bit OS