i heard you can't use more than 3GB of RAM without going to a 64 bit OS so why are some systems coming with 4GB or upgradeable to say 8 GB?

I'm confused

if u have a 32 bit OS the max RAM it can use is 3GB, but on a 64 bit OS you can use more than 3GB.

Basically, you can buy either Windows Vista (an example of an OS) as a 32 bit or a 64 bit.

Some computers can be upgraded to up to 8GB RAM, but to see any benefit of this, you will be needing a 64 bit.

put 2^32 and youll see why
(hint: its 4G )

Yeah, it may just say that the motherboard caters for 8GB and 16GB etc. but you will need a 64-bit OS in order to use it. XP and Vista 32-bit have a shared memory space of 4GB, allocated to the graphics and physical memory in that order, and will use 1:1 at the most. For example if you have 4GB of graphics like me, and 4GB of DDR3 like me, and a 32-bit OS then you would have 2GB of graphics and 2GB of DDR3. You'll find that some 32-bit systems say they have 3.75GB or 3.5GB of RAM and this is because of the shared memory space.