Window scaling was introduced in RFC 1072 and refined in RFC 1323. Essentially, window scaling simply extends the 16-bit window field to 32 bits in length. Of course, the engineers could not simply insert an extra 16 bits into the TCP header, which would have rendered it completely incompatible with existing implementations. The solution was to define a TCP option to specify a count by which the TCP header field should be bitwise shifted to produce a larger value.