The M1 Carbine is the standard by which all PDWs are measured.

[stanc]

After viewing the in-depth contributions to this Thread, this thought occurred to me, What would the M1 Carbine be, if designed today?

Well, the M1 carbine is shorter and lighter than the M1 rifle, and its cartridge is also smaller and lighter than the .30-06 round, but has the same bullet diameter.

There happens to be a weapon which follows that format, and was actually designed to be a modern day M1 carbine. The answer to your question is: The FN P90.