Windows Vista Update

4GB Memory addressability for Vista 64 bit is still crippled by motherboard limitations

by Dru
(Dallas, TX)

I recently upgraded my Dell Dimension E510(P4-3GHz) to Vista 64 bit with 4GB RAM.

All hardware works perfectly except for my really ancient multi-function laser printer which is hooked up via a PCI parallel port card in the computer.

Though the printer driver installed, the printer does not print. While this is not a big deal for me since its about time I got rid of this old printer anyways, the fact that I don't get the benefit of the 4GB RAM is still quite annoying.

The motherboard has 4 RAM slots and can take a max of 4GB RAM with a max of 1GB per slot. After I installed Vista 64 bit happily to make use of thsi 4GB RAM, I only get 3.25 GB RAM usage by RAM.

Vista does say that 4GB RAM is installed in various places and rightly so because it is doing hardware detection of the RAM chips.

However if I look closer in Task Manager-Performance tab and the System Information tool, I found that Physical Memory actually available to the OS is only 3.25 GB!!

This was puzzling, because this made sense in Vista 32 bit because PCI cards(I have 4 PCI/PCI-E cards in my system) get memory mapped and cannot be placed the 4GB boundary for Vista 32 bit to access and as a result Vista 64 bit should have no issues pushing the memory mapped addresses to beyond the 4GB boundary and RAM can be used fully by the OS.

Unfortunately this is not the case as I found out after further investigation.

My motherboard memory controller simply cannot address more than 4GB RAM and that is forcing the (BIOS) to map the devices to within the 4GB boundary as a result robbing the OS of the precious RAM.

In my case, I have a 256MB video card on PCI-E x16 and that straightaway takes away 256MB RAM from RAM, then I have a firewire PCI card, a SATA controller card on PCI-E x1 and a parallel port card.

These get mapped to high order addresses within the 4GB boundary by the BIOS and even Vista 64 bit doesn't get the full 4GB RAM.

This is explained by a Microsoft kb article at http://support.microsoft.com/kb/929605. If you look under the workaround section of this article you'll realize what is happening.

To make full of the 4GB RAM I'll need a motherboard that supports 8GB RAM and then install my 4GB RAM, that way PCI addin cards can be memory mapped to the addresses closer to the 8GB boundary.

So I can install 6GB and have everything available to Vista 64 bit.

However if I install the max 8GB RAM, I'll still have only 7.25GB RAM avaiable to Vista 64bit due the PCI addin cards.

Now, why is this such a big deal to me. I run a laptop on Vista 32 bit and 2GB RAM and I know for a fact 2GB is not optimal for Vista.

You can see in the Task Manager-Performance tab that free RAM is 0 most of the time and it is thrashing disk for most everything.

This is because Vista likes to cache a lot of stuff in memory for better performance unlike older XP. Even with 3.25GB RAM available in Vista 64 bit I have 0 free RAM available in task manager.

I've seen another system with 4GB and running Vista 64 bit no add in cards and the 4GB is available Vista, it makes a huge difference. The free RAM in task manager hovers around 700MB and makes all the difference to the speed of the computer.

I feel 4GB RAM unleashes the full potential of Vista which I have to grown to like. Vista 64 bit is definitely the way to go for most users given how cheap RAM is nowadays.

Vista is a much more solid and responsive OS than XP and very superior in a lot of aspects if it has the RAM it needs.

Also Vista 64 supports most new hardware without issues and support 32 bit applications without much issuses most of the time unless you have a specific liking for a certain 32 bit application that has trouble working with Vista 64 bit.