The mythical 4Gb Vista/XP limit

[Splash]

Hi

After seeing a large number of threads asking in various ways about the 4Gb memory limit I thought it worth my while to put a bit of an FYI up.

The maximum amount of memory that can be addressed by a 32 bit OS (this means ANY 32 bit OS, not just Windows) is 4Gb. Once you take into account your pagefile and a few other things this essentially means that the maximum amount of RAM you can feasibly use is 3Gb (3.5Gb in certain circumstances).

If you need to use 4Gb RAM or more you need a 64 bit OS, be that XP x64, Vista x64 or any other 64 bit OS.



Perhaps worth a sticky, or adding to a current one?

[badass]

Hi

After seeing a large number of threads asking in various ways about the 4Gb memory limit I thought it worth my while to put a bit of an FYI up.

The maximum amount of memory that can be addressed by a 32 bit OS (this means ANY 32 bit OS, not just Windows) is 4Gb. Once you take into account your pagefile and a few other things this essentially means that the maximum amount of RAM you can feasibly use is 3Gb (3.5Gb in certain circumstances).

If you need to use 4Gb RAM or more you need a 64 bit OS, be that XP x64, Vista x64 or any other 64 bit OS.


Perhaps worth a sticky, or adding to a current one?

A few things to add to that.
The pagefile has no effect whatsoever on you seeing less than 4GB memory.
32 bit OS's can address more than 4GB of RAM using PAE, but for a home system it is simply not worth it.
The "hole" seen between 3GB and 4GB on a 32 bit OS where you see less than 4GB RAM available still happens on a 64 bit system unless the motherboard supports logical address remapping or such like. It is unstable at best, allegedly.

A far more pressing problem is the 2GB maximum addressable space available to any process. If you are gaming, you will see this long before you have problems running out of RAM when you have more than 3GB.
using the /3GB switch only helps with applications that are large address aware. No games currently are, although there are mods to make this the case.
Most large address aware applications are server applications.

[PoDd]

As above but its not all strictly accurate. the memory lost from the adressable 4GB on a 32bit system is to system resources and reserved blocks of adressable space, harware adressing etc, long before an OS gets to look at whats left for its use.

using /PAE just allows the OS to adress more memory, beyond its specified limit, it cannot allocate it to any apps or anywhere else, so is therefore pretty useless.

A 64 bit system, by design can adress a huge amount of memory, there are no holes, it is perfectly stable doing so.

PoDd

[bobbyzero]

Good accessible write-up here:
http://www.dansdata.com/askdan00015.htm

[Agent]

Once you take into account your pagefile and a few other things this essentially means that the maximum amount of RAM you can feasibly use is 3Gb (3.5Gb in certain circumstances).

As already mentioned, its nothing to do with the page file.
Its all to do with how the motherboard addresses the components in your system, and how these are passed to the OS.

If you need to use 4Gb RAM or more you need a 64 bit OS, be that XP x64, Vista x64 or any other 64 bit OS.

Not strictly true.
There are ways to bypass this limit (like 36-bit addressing) on a 32-bit OS, and these were used in industry before the event of run-of-the-mill 64bit CPU's were available.
Although with the event of 64bit CPU's and 64Bit OS's, its certainly much easier to use >4GB of RAM and is the way that anyone should go for simplicity, and lack of head banging
Any home user really should just forget about 4GB and a 32bit OS.

using /PAE just allows the OS to adress more memory, beyond its specified limit, it cannot allocate it to any apps or anywhere else, so is therefore pretty useless.

Thats not true im afraid bud
On windows you can use AWE (Address Windowing Extensions) to use up to and above 4GB if needed. There are some rules that must be followed to allow this to happen at speed in a 32bit environment, but it certainly can be done.
http://en.wikipedia.org/wiki/Address...ing_Extensions
You need PAE for AWE to work though.

Having said that, after SP2 for XP32bit, they hard-coded a 4GB limit, IIRC (Remember that XP isn't the only windows OS though)

Linux has its versions too im sure, but im not 100% up on them, so I wont commont on them for the fear of inaccuracy's and being bulled by any passing penguins

A 64 bit system, by design can adress a huge amount of memory, there are no holes, it is perfectly stable doing so.

PoDd

Yup - Id argue this is probably the biggest benefit that 64bit will offer for a while

[Pup]

From the article posted :

By default, an all-64-bit PC will still have the standard big holes in its memory from three to four gigabytes. This is the lowest-hassle way to deal with the problem - just install more than 4Gb of memory, and live with the fact that your 8Gb PC with a 768Mb graphics card only actually has seven-point-not-much gigabytes of visible RAM.

Maybe someone can clear this up for me. Does this mean that if I have 4Gb of memory, then I will actually be able to use no more of it with a 64bit OS compared to a 32bit OS anyways? I see it mentions further down in the article that some motherboards can manage the memory hole to still give you your full 4Gb of memory using x64. (My new system will have a p5k deluxe)

Forgetting about driver issues with x64, and just considering the memory usage.. basically my question is, will a 64bit OS make any more use of 4Gb of memory than a 32bit one, given what is said in that article?

edit : Just found another thread here that mentioned someone saying that 4gb in x64 vista made a massive improvement to load times, so I guess it is worth it

[shaithis]

Pup, not in my experience. I have 4GB on Vista x64 and it sees and uses all 4GB.

[charleski]

And to think I found the difference between Extended and Expanded memory confusing!

[shaithis]

And to think I found the difference between Extended and Expanded memory confusing!

Damn that brings back memories hehe

Think expanded was just a bunch of 64k memory pages IIRC, although lots of apps were picky about whether they would talk to expanded or extended.....which meant rebooting a lot depending on what you were running.

So glad that times change!

[TheAnimus]

Its worth noting that with 32bit windows a lot of memeory is reserved for kernel mode operations.

Without the 3gb switch, you will 'lose' to usermode applications half the system memory.

Another major problem is memory fragmentation, lots of applications will demand memory is alocated in contigous blocks.

So 64bit is a better solution all round, as using 32bit gets rather hacky (you can goto memory segmentation too remeber!).

[Agent]

From the article posted :


Maybe someone can clear this up for me. Does this mean that if I have 4Gb of memory, then I will actually be able to use no more of it with a 64bit OS compared to a 32bit OS anyways? I see it mentions further down in the article that some motherboards can manage the memory hole to still give you your full 4Gb of memory using x64. (My new system will have a p5k deluxe)

Forgetting about driver issues with x64, and just considering the memory usage.. basically my question is, will a 64bit OS make any more use of 4Gb of memory than a 32bit one, given what is said in that article?

edit : Just found another thread here that mentioned someone saying that 4gb in x64 vista made a massive improvement to load times, so I guess it is worth it

If you want to use =>4GB just go with 64bit.
Its easier and will give you far better gains. A 32bit environment will use hacks one way or another to use it. Thats not always a bad thing, but a 64bit OS will do the job so much better

[Pup]

Aye thanks I've already ordered 4gb and Vista 64bit, so was planning to use that anyway. Just that after reading the article it seemed to suggest that I would still only get to see/use 3.x Gb of it even with a 64bit OS, and it was more out of curiosity than anything else