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Is any RAM beyond 3GB is useless?

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ljCharlie Posted: Thu, Mar 13 2008 11:36 AM

This is a topic I'm not quite familiar with. I was told that Windows XP Pro (32bit) does not recognize any RAM that is beyond 3GB. So the question is, is that mean any RAM memory beyond 3GB is pretty much useless? Or that the OS or applications reside in the OS will not utilize/use any excess  of RAM beyond 3GB? I was told that the BIOS does recognize RAM beyond 3GB but just Windows that doesn't. So what is the verdict here? I'm like to know if adding more RAM is any good.

Thanks!

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In order to utilize more than 3gb you will need to run a 64 bit OS.

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replied on Thu, Mar 13 2008 12:05 PM

To really use more than 3 the best solution is to use a 64 bit operating system like Vista 64

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indeed if you want more that 3gb you need a 64bit OS 

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^Bad_Boy^ replied on Thu, Mar 13 2008 12:32 PM

Tell me about it... I have 4gigs on my Laptop, so I have an unusable Gig of ram..

 Anyways in another aspect, how will Dual-Channel work in this sense.. For example as far as I know you need to have the same amount of Ram on each channel.. So if for example someone has 2GB dimm in one slot and 1GBdimm in the other slot.. Will that computer really work in Dual Channel?? Compared to my Setup of 2GB Dimms per Channel, Even though Windows XP only recognizes 3GB's.. I think it's split equally between channels, like 1.5gb per channel.. giving me real Dual Channel setup..

 

So what ya think guys?

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ljCharlie replied on Thu, Mar 13 2008 1:16 PM

From what I've heard from Dell tech support, although the OS will not recognized any RAM beyond 3GB, it is still being accessible by any applications. But I'm not sure if this is true since maybe they may be trying to sell me additional RAMs that I don't need or can't use.

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You actually will still see the benefit of a dual channel setup.  The motherboard is what is controlling your dual channel, so it will address the RAM the same way it would with a 64 bit OS installed.  The OS will feed the instructions to the board and the board will set the addresses accordingly.  So what will happen is that when it goes to write to addresses over your 3GB limit, it will start clearing other addresses in RAM that are currently filled as those addresses become available to be re-written to.  But indeed, you do end up with some addresses that are unused (usually in your 2nd channel of synchronization).  As for benefits of using more than 3GB... Even in a server environment where I have a citrix server and 20+ users it's uncommon for the physical addressing to reach over 2GB, and our domain controller is about the same.  With the new blade server setups and being able to segment your networks so efficiently it's much easier to spread out workloads as well.

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RIZAX replied on Thu, Mar 13 2008 2:29 PM

 If you have (or are buying) a relatively recent computer and are running vista or some version of linux (2.6 kernel) then you should be okay with ram over 4gig.

Even still if your getting a new machine and can afford the extra memory I'd say go for it, it can't really hurt much - were all going to be on vista or some variant

sooner or later. If your using an XP machine then I'd say its a crap shoot, like the above poster says you will still get benefits from having 4gig of memory, but I've 

also read that in some case windows won't perform as well with 4gig as it will if you just had 3 (or just ran with 2 gig in dual as opposed to 4). 

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replied on Thu, Mar 13 2008 4:10 PM

Some programs can take advantage of memory in xp above 3gb using a "hack" in a sense. But like all things that use "work arounds" it's not as good as solving the problem for real. In this case moving to a 64 bit OS.

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ice91785 replied on Fri, Mar 14 2008 12:21 PM

RIZAX:
Even still if your getting a new machine and can afford the extra memory I'd say go for it, it can't really hurt much - were all going to be on vista or some variant

 

Just to clarify -- Vista still will only support 3-3.5 GB of RAM unless you get (as was said a few times now) 64-bit Vista. Actually I have read a few articles that in general MS is going to offer improved 64-bit support/performance. Morever retailers ar going to start offering MORE 64-bit native OS's at places like Best Buy and Circuit City etc....

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trueg50 replied on Thu, Mar 20 2008 6:15 PM

 It is called PAE or "physical address expansion"

 

Basically the issue is that a 32 bit processor (or OS) can only address 2 ^32 bits, while a 64 bit processor and OS can address 2 ^64 bits.Your RAM is the last thing being addressed, so you have to take your total RAM, and chop off the amount of System memory, GPU memory, sound card memory and you are left with ~3.25 gb if you have a 512 mb graphics card and onboard sound.

 

 Indeed PAE is not nearly as effective as an actual 64 bit OS, but it does sort of work.

 

I am using x64 Vista right now, and absolutely love it. Every program I use has an x64 variant, and I have yet to have an issue with instability or finding drivers. Though this may be more attributed to me using Vista than the x64 part, though it is a testiment to its popularity.

 

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ice91785 replied on Thu, Mar 20 2008 9:41 PM

trueg50:
Indeed PAE is not nearly as effective as an actual 64 bit OS, but it does sort of work.

 

Not to mention that PAE can cause issues with writing to memory often times with system files -- from what I have read PAE "extends" your available writable address but will not index them in the way that the reason of the RAM is indexed so often memory writes can be "moved" and cause BSODs

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AjayD replied on Fri, Mar 21 2008 3:57 AM

 This question is just out of curiousity, but what is the maximum amount of ram a 64 bit OS can handle? The reason I ask is because I remember reading on here recently about how the three channel DDR3 memory controller that Nehalem will bring will support up to 18GB of memory. I can't think of any reason why this much memory would be necessary at this point in time. Though if money wasn't a concern I would have it simply for the sake of having the best.

 

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trueg50 replied on Fri, Mar 21 2008 8:03 AM

 Vista home premium can handle 16 gigs, while ultimate can handle something along the lines of 128 gb.

 

Right now I Superfetch is re-learning everything so RAM usage is at 2 gb, normally it is at 1.5.

However Vista scales, so at 2 gb it will use 1 gb normally, and with 1 gb it will use 200-400 mb.

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 32 bit wont use over 4 Gbs i believe/Big Smile

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