What is difference between 32bit os and 64bit os ?

Answer 1

Go and use Google search on that question :)

Answer 2

64bit has access to more ram. I think the limit for 32bit is 4GB. So if you need more than that, 64bit is definitely the way to go.

Answer 3

Here's an article comparing 32- and 64-bit architectures. 64-bit is so big that manufacturers actually still limited it.
You may wish to pay special attention to the unusable gaps in 64-bit Windows (and just how "tiny" user space is compared to addressable memory):
https://docs.microsoft.com/en-us/windows-hardware/drivers/gettingstarted/virtual-address-spaces

The separation of User Space (memory bottom) and System (virtual memory top) can also be a security measure -- just check whether high bits are set.
To get a feeling for just how big the unused gap is (in decimal) open a Python program and paste this:

print(0x000007FFFFFFFFFF) # top of user space
# gap
print(0xFFFF080000000000) # bottom of system space