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I am not quite understanding this at all.. If The processor controls how much total ram memory it can handle, how come motherboards limit them selves? For instant if your buying an intel quad core processor that is of course 64 bit native, in which can handle up to 16gigs of ram, why do some motherboards only state that it can handle up to 8 gigs and others where it seems to be expected at 16gigs? what am i missing here?

Hello Codex let me see if I can explain.

Ok I will explain Vista but it is same princible as XP.

The princible of limitations is due to many things.Which include hardware,chipset,CPU,even the manufacuture setting limitaions on there hardware even down to choice of installed OS.

Ths simplist idea of the limitations is also a persons budget.Manufacturers will make cheaper boards that take smaller CPUs,less RAM ,less hard drive connections,less CD/DVD rom drives than can be installed.

Back in the day most people got by with 256MB or less of RAM and if you were a bit of a power user, you might have gone for 512MB or even 1GB. However, PCs are starting to appear with much more RAM and it's cheaper than ever to upgrade a PC with some serious amounts of memory. How much is actually usable though is another matter and there are a few limitations you need to be aware of to avoid disappointment when you find that even though you installed 4GB in a PC, your PC either can't see it all or won't let you use it.


Version32bit Limit 64bit Limit
Windows Vista Ultimate 4 GB128 GB
Windows Vista Enterprise 4 GB128 GB
Windows Vista Business4 GB128 GB
Windows Vista Home Premium4 GB16 GB
Windows Vista Home Basic4 GB8 GB
Windows Vista Starter1 GB n/a

Windows Vista and Memory

Vista comes in two main flavours 32bit and 64bit. 32bit Vista can, in theory cope with up to 4GB of RAM with 64bit Vista going to 128GB. In that respect it broadly mirrors Windows XP. However, things aren't quite that straight forward as this table shows. The limits are fairly sensible though at this point in time and not many people with 64bit Vista Home Basic are going to feel hard done by with an 8GB limit. Any real power users are going to have Vista Home Premium or Vista Ultimate and these have quite enough capacity for any current or foreseeable uses.
So, you go out, buy 4GB of nice fast RAM for your PC, load it up and reboot. With trembling hands you check how much memory you have and Windows reports 3GB. Huh?
This is where is starts getting messy. Just how much memory you actually get depends on many things. Let's start at the most basic level.
BIOS

Your BIOS may limit how much memory your system can use. Even if you can physically put in 4GB, the BIOS may only recognise 2GB or some other value. If you're lucky, you can update the BIOS and get access to more but not always so check your motherboard and BIOS's specs first. Most decent manufacturers continue to produce updated BIOS's for boards long after they've stopped making them so if your PC is a year or two old, you are probably going to be in luck if this is your problem.
Hardware

The motherboard itself may have constraints from the chipset which could limit the maximum amount it can cope with - some boards can only cope with 8GB, some much less, again, check first. More of an issue is that a large chunk of a PC's address space (the range of memory locations it can use) are reserved for use by the different bits of hardware you can have plugged in. Your graphics card, sound card and other bits of kit all reserve ranges of addresses for communicating with the system via memory mapped I/O or MMIO. To help get around any clashes, Vista's 32bit versions actually limit how much memory you can use in practice to 3.25GB (See support.microsoft.com/kb/929605)
Most hardware is designed to map itself above the 2GB area as historically, the chances of any real memory being there, especially in a consumer environment was vanishingly small. On a typical system, according to Microsoft, you'll lose between 200MB and 1GB of address space and thus usable memory to your hardware. One of the worst culprits is graphics cards - they might not use 512MB of actual memory but they will use 512MB of address space stopping you using the memory that is physically there.
You can see here a typical PC's MMIO usage. You can check your own by going to the device manager and selecting the "View Resources by Type" menu option.
If you use a 64bit version of Windows Vista you'll be able to use more than 4GB of memory but you'll still get hit by the MMIO issues so if you install 8GB of RAM, expect to use perhaps 7GB.
Conclusion

We'd say that if you're running a 32bit version of Vista (or XP for that matter), not to bother putting in more than 3GB of memory - you just won't get the use of anything more. Certain companies such as Dell actively market PCs with 32bit Vista and 4GB of RAM - surely a waste although their small print does warn you'll only get to use 3GB of it.
On the other hand, if you are running a 64bit version, you are better placed but make sure your BIOS and motherboard are able to cope with the amount of memory you intend installing to avoid disappointment and don't forget, you'll still be losing some of it to MMIO.

I have marked your thread as "Open" so others can give there opinion on this for you.

JB.

Well explained Jelly Bean.

Are there limits on Ubuntu and the like?

Thanks!, to clarify on the hardware aspects of it, this is pretty much the difference on if the company decides they want to build one MB with 8gig max, vs a MB with 16gig max based on motherboard quality and cost? its not so much of a factor as its not possible? From where i have been getting confused at is, if the MB are handling these quad pumped processors that can understand a X amount of bits from the registers, then why are these companies limiting their motherboards via RAM < CPU.

Some motherboards state that its LGA 775 that is 1333/1066 FSB with ddr2 1066 native ram at 8gigs max

others state that they are LGA 775 1333/1066 FSB with ddr2 1066 ram native at 16gigs max..

What inside the chipset, causes this? MY assumption would be the Address bus and External Bus lines to the processors?

If this is the case then is it correct that these companies do this to make cheaper motherboards vs a more expensive mothrboard , for marketing strats?

Elpmek that would depend on the computer system specifications.Also there is a limit but the amount of RAM that can be installed differs in peoples opinions.

Minimum system specs are:

Intel 486 processor
32 MB of system memory (RAM)
300 MB of disk space
Intel Pentium 66 MHz processor
48 MB of system memory (RAM)
468 MB of disk space
VGA graphics card

But to be honest on the absolute minimum is realy not a good idea.

A Dell Mini 9 is apparently limited to 1 gig RAM.

Ok what I asume is right it depends again on your computer system specs I find I maybe wrong but Ubuntu may support upto 4-8 gig of RAM.

Again depends on lower spec machines or higher specs.If the computer is to be used for games then you would need a higher spec in hardware just the same as XP and Vista for the system to run higher ended applications.

I think it's because of technology "leap frogging". Let's say I'm a manufacturer and I've all these obsolete motherboards, which are perfectly adequate, but only perform to certain specifications. They've still got to be sold.

maybe I'm just looking for an explanation thats just so dumb I'm looking too deep into it? So why not make a mobo that can handle 128 gigs of ram? whats holding them up? what determines that on a motherboard it self?