what is eating my memory? Windows 7 in VirtualBox

this is rather weird. I have a work laptop with Ubuntu and Windows 7 virtual machine in VirtualBox in it. In that VM I usually run just 2 RDP sessions, SciTE editor, Evernote, Total Commander, but once I start Excel or FireFox it starts to complain that the computer is low on memory and I should close somem programs! It has 2.3GB of RAM assigned, so how can this amount of memory not be enough for these apps? I remember using a Windows 7 machine with 512MB RAM just fine back in the old days. Task manager does not really help me with that. Any idea what could be holding all this?

Paging file is set to system managed for C drive and there is 10GB free out of 40GB total on C:

c:\pagefile.sys file was 960MB, but when I got into settings I get this error. Then I saw it was "no pagefile", so I set it again to system managed. But anyway, shouldn't it work without pagefile also? What is using 2GB of RAM? I can't see it in Process Explorer either.

EDIT2:
so pagefile seems to be working now, but I am still curious why is commit so high and what does this number actually consist of...

Answer

The official minimum memory requirement for Windows 7, 64-bit is 2GB. You have that. So you should be okay. But it's a bit tight. That means you need to be able to make use of RAM effectively. Without a working page file, you can't do that. Fix the page file and the problem will go away. The page file will likely not be used, it just needs to be available.

It's a bit complicated to explain accurately, so permit me a grossly oversimplified explanation. Imagine if a process asks Windows to reserve 1GB for it. You'd be pretty annoyed if it said no. You have lots of RAM free, more than 1GB, and the program only wants 1GB. So Windows says yes. But say that process doesn't use any of that memory. Still, Windows can't assume it won't, so it has 1GB of RAM that it can't let any other process reserve. Ouch.

With a working pagefile, Windows knows that it can make free RAM whenever it needs it by writing to the page file. So it can let other processes use and reserve memory without having to fear that it will promise more than it can deliver.

With no page file available, Windows can't commit more memory than it has RAM, and that makes for horrifically inefficient use of RAM.