I thought I had this fixed. My solution below helped. But I just discovered that now when I refresh msinfo32 again and again, Available Physical Memory is gradually declining with time.
When I first checked it it was 6.05, now it's 4.89, or over a gigabyte lost in an hour.
And it should be more like 7.xx. After a reboot it start out higher and after many minutes is much lower. Dare I say a system memory leak, or what?
[My previous answer:] I had to update my chipset driver. Finally after many years of hunting for this solution!
I'm running Window 7 x64 on a hp pavilion dv7t-2200. Have 8gb installed, but was only seeing about 1/3 of that used at most ever (via the ms cpu/memory usage 'gadget' indicator).
First I updated bios but that didn't do it.
But in the process I learned of a very good tool. Check this out: Run msinfo32 at the start/search box.
It reported that I had:
"Total Physical Memory (RAM) 8.00 GB", and
"Total Physical Memory 7.97 GB", but that
"Available Physical Memory was only 3.9x GB". (aprox., because I didn't record the actual number)
Once I updated the chipset driver I got "Available Physical Memory 6.49 GB". I don't know why it's not closer to 8 gb, but I'm happy to have gotten it to up it to this. Perhaps part of it is used up in managing the other part of it.