WINDOWS XP IS CALLED XP BECAUSE XP IS 2001 IN ROMAN NUMERALS
WHAT
“The more standard MMI was avoided, because the MRNSDK (Microsoft Roman Numeral Development Kit) doesn’t fully support the M symbol for 1000. Of course, P is not generally included in the Roman numeral system; it was quietly added between the 1.01 and subsequent 8.0 releases of the MRNSDK. Though undocumented, and possessing obscure semantics, the P extension is widely used. In any case, it is easy to verify through experimentation that XP = 2001”