The addressing scheme used for the TCP/IP protocols
is IP version 4 (IPv4). This scheme uses a 32-
bit binary number to identify networks and end
stations. The 32-bit scheme yields about 4 billion
addresses, but because of the dotted-decimal system
(which breaks the number into four sections of
8 bits each) and other considerations, there are
really only about 250 million usable addresses.
When the scheme was originally developed in the
1980s, no one ever thought that running out of
addresses would be a possibility. However, the
explosion of the Internet, along with the increased
number of Internet-capable devices, such as cell
phones and PDAs (which need an IP address), has
made running out of IPv4 addresses a serious concern.
The chart shows the trend of address space,
starting in 1980. It shows the address space running
out sometime before 2010.