Question regarding RAM and 32-bit systems

[Djohn]

From what I've seen, every single computer distributor's website will tell you that you need a 64-bit system to utilize more than 3 GB of RAM. However, a good friend of mine told me that the limit is actually 4 GB, and Wikipedia agrees:

The range of integer values that can be stored in 32 bits is 0 through 4,294,967,295 or −2,147,483,648 through 2,147,483,647 using two's complement encoding. Hence, a processor with 32-bit memory addresses can directly access 4 GB of byte-addressable memory.

Now, I just recently ordered a new laptop, and my understanding is that an Intel C2D T9300 CPU is no guarantee that I will be running 64-bit Vista (Lenovo's website doesn't specify 32 or 64-bit). The system will come with a single 2GB stick of RAM, but I've also ordered a second 2GB stick off of newegg.

The problem is that I don't trust Wikipedia to be entirely realistic, and I'm afraid there might be some artificial restraints on recognizable memory (as exist in 64-bit Vista). Of course, I'm also willing to accept the alternate conclusion that computer distributors either a) don't know what they're talking about or b) are lying. So, my question is this: Can the average 32-bit system actually recognize 4GB of RAM in practice or am I out of luck if I'm running 32-bit Vista?

Edit: Also, please correct me if I'm wrong about the OS not necessarily being 64-bit (all C2D CPUs are 64-bit), as that would make the whole issue moot. If it matters, the laptop in question is a Lenovo Thinkpad T61.

[Cephius]

It's true that 32-bit Windows Operating systems can technically have 4GB of addressable virtual memory, however only 3GB will be available to you. 512MB - 1GB (depending on OS) is automatically allocated to the system kernel and other system-level processes. There's no situation where you'd be able to address all 4 GB unless you use a 64-bit operating system, where there is no limitations (except physical).

An operating system and a processor being 64-bit are not the same thing. You need a 64-bit operating system to be able to address more than 3-3.5GB of ram.

[Djohn]

An operating system and a processor being 64-bit are not the same thing. You need a 64-bit operating system to be able to address more than 3-3.5GB of ram.

Yeah, that's what I meant, I know I've got a 64-bit processor but I don't know if it comes with 32-bit or 64-bit Vista. Thanks for the prompt reply, I guess I'd better hope it's 64-bit then... Either way though, it's a vast upgrade from my current system, so it's not the end of the world if I can't have 4GB of RAM.

[Shuemue]

You'll barely notice a difference.

[levish]

I wouldn't bother for a laptop and 4gb max ram, if you were talking about more than 4gb i'd bother to go with 64bit.

p.s. might want to disable superfetch when you get your laptop

[Zosi]

The replies so far are about 98% right. All 32-bit OSs do indeed reserve some of the "high" memory space, generally about 700mb, leaving you with around 3.3gb of the first 4gb available. However, non-Windows OSs and a few select versions of Windows support something called PAE that lets the OS address up to 64gb of memory, with each single application being limited to a 32-bit pointer unless they support PAE themselves.

Under PAE, the ~700mb of address space is still reserved just below 4gb, but it results in no actual loss of usable memory space because the OS has enough address space AFTER 4gb to map in the "missing" physical RAM.

Server versions of 32-bit Windows support PAE, and desktop versions of XP SP2 or higher and Vista "support" it, but limit themselves to 32-bit addresses (4/3.3gb) anyways because of driver compatibility issues.