Thinkpads Forum

Folks - I know that the 4GB topic has been frequently discussed. So I have no questions about PAE, matched DIMMs, 32-bit addressing, and such. What I am looking for is insight into what happens to the 1GB of space above the 3GB mark. Is it simply lost? Or does the system make some use of that space?

A post I read on another board says (not directly discussing the T61P): the chipset reserves approximately 1GB at the top of the 4GB address space for system functions - things like BIOS firmware, digital media interface, PCI Express ports, and memory-mapped I/O - of these, the PCI Express element is by far the biggest; and might vary according to how much RAM is on your graphics card. The result is that when you boot, the board declares: "memory consumed by system resources: 1024MB." To put this another way - this memory is not really being "consumed" - it is just that the board can't really address it as the address locations are already used to point to other things.

If this is true for most Intel processor system boards, then it would seem that using 4GB on a T61P could provide more usable space, for Windows and applications, below the 3GB mark; as system functions have a place to play outside the space usable by Windows. Again, if true, I would assume that a system with 3/2/1GB also loses some address space to system functions - thus leaving less than 3/2/1GB for Windows and applications. Or does the T61P just allow addressing (for system functions, Windows, and applications) below 3GB - thus a system with 4GB has NO benefit over a system with 3GB?

If anyone has a true understanding of this, and can provide a clear, concise, explanation, it will be GREATLY appreciated!!

The main difference between 3GB and 4Gb would be symmetric dual channel mode but the difference typically is not perceivable.

Usage of the entire 4GB depends on what OS you are running. Erik wrote up an aweome summary here:
http://forum.thinkpads.com/viewtopic.php?t=49703

I believe I have found the best discussion on this topic: http://support.microsoft.com/kb/929605/en-us .

There are also links available from this page that provide more insight.

I guess support.microsoft.com can somtimes be useful!

Alabama wrote:I believe I have found the best discussion on this topic: http://support.microsoft.com/kb/929605/en-us .

the article says exactly what my tests show above...

microsoft wrote:However, to avoid potential driver compatibility issues, the 32-bit versions of Windows Vista limit the total available memory to 3.12 GB.

on top of that, the OS can only use addressable memory.   in the case of 32-bit windows this is limited to the lower 3GB in a system.   as i mentioned in my write-up (which microsoft also explains in theirs), both the OS and the chipset must support memory hoisting to be able to address memory above the 4GB mark, therefore allowing over 3GB to be addressed when 4GB is installed.   the only "32-bit" windows OS capable of this is windows server 2003 -- and it's technically a 36-bit OS.

so, i don't see any new information here.   4GB in a T61/T61p is limited to 3GB addressable space when a 32-bit OS is used.   anything more than 3GB is absolutely wasted.

if there was a way around the limitation then i probably would have found it.   i worked on the OS tests for about three weeks straight trying to find fixes, switches, or other loopholes which would allow more than 3GB to be addressed.   everything i tried showed the 32-bit OSes to be limited to 3GB and nothing above this space (well, nothing above 3070MB in vista, that is) could be addressed by the system.   it was wasted.

Alabama wrote: thus a system with 4GB has NO benefit over a system with 3GB?

that's correct.   now were back where we started.

if you need more than 3GB then you need to use a better OS.   it's just that simple.

I can push 3gb of RAM usage with some of the applications I run (Vista inside a VM, plus Mac OSX inside another VM given generous amounts of RAM)