The numbers don't add up?
They do to me.
4096 is clearly right as 1024 x 4 = 4096 proving that your full 4Gb is properly recognized.
256 + 64 + 1215 = 1535
1535 ~ 1519 (where ~ means approximately).
Sadly, there is nomenclature inconsistencies in the computer industry when it comes to how many bytes are in a kilobyte. In mathematics, 1 kilo = 1000. But in digital (binary math) electronics, 1 kilo = 1024. And to make matters worse, marketing weenies have stepped in to make it more confusing. For example, hard drive makers use 1000 because then they can claim (advertise) more Gb per drive.
RAM makers, however, use 1024. System Monitors/Information tools use whatever the programmer wants to use. The developers may use 1000 or they may use 1024 - there is no established standard - hence confusion and differences in published specs - which may explain some of the tiny
differences between dxdiag and your Display Advanced Settings readings.
Also, I should note that today's integrated solutions often come with a little bit of dedicated graphics RAM on the motherboard too. That is, in addition to large chunks of system RAM stolen... err, I mean "shared" by the integrated graphics solution, it may have a small chunk of dedicated graphics RAM too. That may be some or all of the 64 and 256 values.
Anyway, IMO, all your RAM is being recognized and used. I will also add that when it comes to Memory Management and the efficient use of RAM, the PhDs and super computers at Microsoft have it figured out. That is, unless you too are a PhD in Computer Systems Engineering, let Windows manage your memory - "ALL" your memory to include your "virtual" memory which is made up of System RAM plus your Page File. Don't mess with the default settings. Let Windows manage it all - even if you have gobs of RAM installed.
Windows 7 is NOT XP
. We (all of us) must NOT assume what was good for XP is good for W7 (or W8). It probably isn't.
And finally, this is a "netbook" computer. Not a notebook or PC, or a PC replacement. Therefore, as a netbook, it has "dedicated features" (which vary by each maker) and which consume "dedicated resources". And they have very limited customization capabilities - by design.