Windows 32 bit will only be able to use 3.5 gb of ram no matter how much is installed , you could have 8 gb installed and it will still only see 3.5 gb of it.
Windows 64 bit will see and be able to use all the ram that the motherboard will support. Most motherboards today will support 32 gb of ram with some going up to 64 gb but you need Windows 64 bit to use all of the ram.