Earlier quoted context omitted.
IPv4 as designed didn't support anything like a few billion addresses. We had to invent CIDR to get there, years later.
Are you sure about that? If we're talking as IPv4 as specified in RFC 791[0] (dated September 1981) it seems to support billions of addresses already: > Addresses are fixed length of four octets (32 bits). An address begins with a network number, followed by local address (called the "rest" field). There are three formats or classes of internet addresses: in class a, the high order bit is zero, the next 7 bits are th…
IPv4 was running out of class B's, those 64k address chunks, when CIDR was introduced.