Sorry, but you're still incorrect.
On a machine with minimal addon cards, Windows (32-bit) can and will report a full 4GB of RAM, and it is fully usable by the OS.
On most modern machines, you have enough other devices sucking address space below the 4 GB barrier, so on a typical machine you will "lose" between 500-1000 MB of RAM. So, given CURRENT hardware and CURRENT Windows, it's true that you often lose 1GB of RAM. Our unlucky W500 loses a whopping 1.5GB of address space below the 4GB mark, so you can only use about 2.5GB of physical RAM on a 32-bit (client) OS with this laptop. If you're willing to run 32-bit Win2k3 or 2008 Server, you can use all 4GB without trouble.
This problem comes about due to an artificial limitation placed into client-grade Windows. With the correct hardware, and an older copy of XP (pre SP2, might even need pre SP1) you CAN use all 4GB of RAM. One badly written driver will repeatedly BSOD such a machine though, which is why MS put in the aforementioned artificial limitation. They assume that drivers used on a server OS will be properly tested, which is why they don't have this limitation on 32-bit Server.
The "3 GB with a hack" thing has absolutely nothing to do with physical RAM. The /3GB switch (which incedentally, isn't "supported" on anything other than a Windows Server OS) changes the division of virtual address space from 2GB per process to 3GB per process. Virtual address space is not the same as physical RAM. Please don't confuse the two. Every running process on the system "sees" a 4GB chunk of virtual address space. This would even happen on a PC with 256 MB of RAM - 32-bit windows gives each app 4GB of VAS. By default, that 4GB is split so the process gets 2GB, and the kernel and drivers get the other 2GB of VAS. Every single process on the box has its own 4GB of VAS. Through the magic of paging to disk (both data to the pagefile and images back to their original files) you can do this.
The /3GB switch just twiddles the slider on the VAS so an individual process can have more VAS for itself - photoshop with big data would like this, for instance. This has zero to do with your physical RAM though.
It's not an argument at all - it's technically-minded people who are misinformed about the internals of Windows trying to explain it to lay-people and screwing it up in the process. When someone who actually does this for a living slaps down a correct technical explanation, everyone's eyes glaze over and they completely ignore it. 
Here's another VERY common misconception. Did you know that when you minimize a program and it eventually gets "paged out," the whole program isn't just thrown into pagefile.sys?
I'm sorry to get all "preachy," and I'm not trying to single you out, but I hate seeing misinformation about this "issue" being spread around. It took me several days worth of reading and research (spread out over a year or so, not all at once) to finally wrap my head around how all of this works, and there are times I still have to go back and reference bookmarks or TechNet to get the finer points correct. 
I don't mess with the guts of Windows for a living, but I know people who do and have read their comments. I'm just an IT guy who REALLY likes to know what he's dealing with. If this were Linux I'd probably be reading source code...
So these are the specs of my W500 memory. SO if i understand correctly, my total is 2.99GB because vista cuts off somewhere around there, and the remainind available 1.82, is how much my software can use after my hardware eats it up first???, and what is the deal with this total virtual memory, what is the good of that?
erik wrote:
a 64-bit OS will read installed memory up to 2 terabytes. your T400 will show 4GB installed and addressable by the system. some of that will still be mapped out due to your hardware though.
Not on x64. The hardware does use address space, but since the T400 is a modern system with correctly functioning hardware remap, the RAM will get mapped above the 4GB mark and thus avoid any conflicts with the addresses from add-in equipment.
If somehow you managed to install 2 TB of RAM then you might run into issues because you'd be out of space to remap to...
