What is the main difference between ipv4 and ipv6?

Basically, the main difference is the address size. IPv4 uses a 32-bit address system. This gives us about 4.3 billion addresses, and we've almost run out of them. That’s why we have IPv6. It uses a much larger 128-bit address. This provides a practically unlimited number of addresses for all our future gadgets. So, it's the necessary upgrade to solve the address shortage problem and keep the internet growing.