A typical IPv4 address looks like or . Where it can not grow after 255.255.255.255 (subnet mask). IPv4 uses 32-bit (four-byte) addresses, which limits the address space to 4,294,967,296 (232) possible unique addresses. However, some are reserved for special purposes such as private networks (~18 million addresses) or multicast addresses (~270 million addresses). This reduces the number of addresses that can potentially be allocated for routing on the public Internet. Read more about IPv4 and IPv4 space exhaustion on WiKiPedia.
Now IPv6 (Internet Protocol version-6) is the one who's going to save us from this space outage and will be the successor of IPv4. Windows, *nix and other software have support for IPv6 since quite long time now. Typical IPv6 address looks like 2002:7c7d:f78d::7c7d:f78d.
Here I am sharing this wonderful info-graphic prepared and published by FOCUS Research.