Windows Vista Windows Vista 4GB Ram Limit

[guest_9323wk]

Hi,

Am I right in thinking that Vista 32bit reads that there is 4gb in the system but it will not show up in Vista? but it will still use it right?

Thanks,

Wiz

 

[floppybootstomp]

Vista 32 bit with SP1 installed will show 4Gb of memory in device manager.

It's my understanding though, from reading lots of articles and debate on this subject, that it won't fully utilise it, the 32 bit software is not capable.

Again, I understand that Vista 32 bit will only use around 3.3Gb of installed memory.

But to be honest I still don't really know for sure. The arguments do seem to point toward not fully using 4Gb though.

And if anybody here claims it either does or it doesn't, please don't just blindly state that as so, kindly provide proof with a technical explanation or supply links.

 

[guest_9323wk]

Thanks for the reply Flopps.

 

[muckshifter]

Do I really wan't to answer this again ??


OK, just once more ...


If you are running 32-bit Windows, you must live with it. You will not ever see all 4GB of RAM you've paid for.

If you are running 64-bit Windows, you may have to live with it. Depending on your motherboard's chipset, your system may support memory remapping. If so, you will be able to use all 4GB of RAM.


The boring Details:

In any 32-bit operating system, the virtual address space is limited, by definition, to the size of a 32-bit value:

232 = 4,294,967,296

4,294,967,296 / (1,024 x 1,024) = 4,096

As far as 32-bit Vista is concerned, the world ends at 4,096 megabytes. That's it. That's all there is. No más.

Due to an architectural decision made long ago, if you have 4GB of physical RAM installed, Windows is only able to report a portion of the physical 4GB of RAM (ranges from 2.75GB to 3.5GB depending on the devices installed, motherboard's chipset & BIOS).

This behavior is due to "memory mapped IO reservations". Those reservations overlay the physical address space and mask out those physical addresses so that they cannot be used for working memory. This is independent of the OS running on the machine.

Significant chunks of address space below 4GB (the highest address accessible via 32-bit) get reserved for use by system hardware:

• BIOS – including ACPI and legacy video support

• PCI bus including bridges etc. • PCI Express support will reserve at least 256MB, up to 768MB depending on graphics card installed memory

​

What this means is a typical system may see between 256MB and 1GB of address space below 4GB reserved for hardware use that the OS cannot access. Intel chipset specs are pretty good at explaining what address ranges gets reserved by default and in some cases call out that 1.5GB is always reserved and thus inaccessible to Windows.



When looking at memory in systems there are three questions to ask that will tell you the maximum amount of memory your O/S will be able to use:

1. What O/S Edition have you installed?

a. 32-bit Windows is limited to a maximum of 4GB and cannot see any pages above 4GB. b. 64-bit Windows can use between 8GB and 128GB depending on SKU.

​

2. What address range can your processor actually access?

a. Typically that’ll be 40-bit addressing today for x64 (Intel EM64T/AMD64), but older processors may be limited to 36-bit or even 32-bit

​

3. Can your system’s chipset map memory above 4GB?

a. Mobile chipsets on sale today cannot (but that may change with time) b. Newer workstations (which use chipsets developed for single or multi-proc servers) usually can.

​

Windows can remap memory from below 4GB to above 4GB and use it there, however, that relies on the three points above:

1. Can Windows access memory above 4GB?

a. 32-bit – NOb. 64-bit – Maybe (due to chipset limitations)

​

2. Can your processor access memory above 4GB?

a. If it’s recent then it might, and if it’s either AMD64 or EM64T it’s almost certain

​

3. Does your chipset allow pages to be remapped above 4GB?

a. Probably not – and that’s what’s catching people who install 64-bit Vista to work around point 1 – they find they still cannot see above 4GB

​

In some cases, OEMs may be able to tweak their BIOS to reserve less memory for platform use, but we’re not talking a huge difference (ie, 100’s of MBs).



In the end a 32-bit OS and/or application can only, ever, handle 4GB of memory at a time, the AWE stuff just swaps chunks of memory in and out of that 4GB space, thus fooling the application and OS into using more space than it can “see”.



Physical Address Extension (PAE), extends the physical address space to 36-bits if your HW supports this. For most operations, the processor execution units will only see 32-bit addresses, the MMU will take care of the translation to 36bit addresses. No swapping here, only page translations (which are used regardless of PAE being on or not), this is a fundamental feature of any virtual memory operating system.



The OS and apps only see 32-bit addresses because the registers are limited to 32-bits (hence the “32-bit” architecture nomenclature). These are linear addresses which are extended to 36-bits in the translation to physical addresses, but they never show up in registers since there’s no room. It’s all internal until the address lines coming out of the chip are toggled. Thus my comment above about “if your H/W supports this (PAE)". I’m not going into how that works …



So, the OS can happily handle up to 64 GB of memory for 32-bit PAE-able systems.



Hope this helps explain the whole, ‘Why can’t I see 4 Gig of RAM in my system?” thing …

http://support.microsoft.com/kb/929605/en-us

http://en.wikipedia.org/wiki/Physical_Address_Extension

http://en.wikipedia.org/wiki/Address_Windowing_Extensions

as early as 2004 ...
http://www.brianmadden.com/content/article/The-4GB-Windows-Memory-Limit-What-does-it-really-mean-

http://blogs.msdn.com/oldnewthing/archive/2006/08/14/699521.aspx


... I now retire from this discussion.

 

[guest_9323wk]

edit: I've snipped the quote Wiz, as it's rather long! - Ian

Cheers for the reply, and the links Mucks,

Thanks,

Wiz

 

[floppybootstomp]

So is that a yes or a no then?

 

[Adywebb]

Looks like a maybe

Mucks....I know you've answered this many many times before, so how about making a sticky of one of them so you don't have to go through it all again?

 

[floppybootstomp]

Mucks....I know you've answered this many many times before, so how about making a sticky of one of them so you don't have to go through it all again?

Aye, that crossed my mind as well.

My own confusion, funnily enough, stemmed from one remark Mucks made shortly after Vista SP1 was released when somebody asked if Vista 32 Bit would use all 4Gb of memory as it was now shown in Device Manager.

Mucks replied something to the effect of 'It will certainly make use, one way or another, of all 4Gb' which I guess may be a little vague.

Then I read elsewhere people taking a pop at Microsoft for showing 4Gb when Vista 32 Bit (or XP for that matter) couldn't possibly use it all. So I was understandably confused.

And I guess I'm too damn lazy to do my own research because I can understand this stuff if I've a mind to, I do have a qualification in Digital Techniques after all, albeit gained 21 years ago

Bottom non-techy line is: Even if a Microsoft 32 bit operating system uses 4Gb of memory or not, having that much memory sure does improve performance, it does for me anyway.

And at this moment in time good quality memory is reasonably priced so it's a viable option.

 

[muckshifter]

It is quite simple ... use 4gb ram for 32bit OS and live with what is being reported, or, stick with 2gb and be happy-ish.

Any 32bit OS can only use up to 4gb ram ... it's how it uses that 4gb & how it reports it to the user that is confusing everyone. It is also an inconsistent report depending on your hardware.

The biggest bunch of people that did the initial shouting at MS ware the ones that bought a 64 bit OS but never bothered to check out the criteria that was ALSO needed to run a 64bit OS ... the hardware.

 

[Waynos_Face]

Why not just play it safe and buy 3 gig?

 

[Abarbarian]

Will this help clarify at all . It is a screenshot of my present pc running a linux distro . I have 4 GB of ram and a dual core cpu .

 

[Adywebb]

Will this help clarify at all.....

Nope.......

 

[Abarbarian]

Nope.......

Mebees this will help then as this seems to have developed into a general " 4gb ram thing" .They are talking about linux in the first part and windows later on .

When using [font=Verdana,Arial,Helvetica,sans-serif][font=Verdana,Arial,Helvetica,sans-serif]applications[/font][/font] compiled for 32 bit, there are some subtle advantages and disadvantages to a 64bit OS, but nothing that actually matters very much.

A 32bit application can use 4GB [font=Verdana,Arial,Helvetica,sans-serif][font=Verdana,Arial,Helvetica,sans-serif]virtual [/font][/font][font=Verdana,Arial,Helvetica,sans-serif]memory[/font] under a 64 bit OS, but can only use 3GB under a 32bit OS. But if you were running applications for which the 3GB restriction mattered, I expect you would know that and already take that into account.

A 64bit OS can do a better job of managing very large amounts of file caching. For the way I use my Windows system, I know that the file caching in XP64 is a great advantage over XP32. But I don't know whether the difference is as big between 32 and 64bit [font=Verdana,Arial,Helvetica,sans-serif][font=Verdana,Arial,Helvetica,sans-serif]Linux[/font][/font], and I have no idea whether your use of your computer depends heavily on file caching.

 

[Waynos_Face]

I think that with the SP1 released for vista 32 bit this now solves the issue?

 

[guest_9323wk]

Hi Guys,

Thanks for all your replies they have been helpful, therefor if anyone feels that it might be a good idea to close this theard then do.


Thanks,

Wiz

 

[Adywebb]

If your happy Wiz, then closed it is