What is SP1 (Service Pack 1)? What is it for?
This is the first version of Windows xp (first service pack).
There is also Service pack 2, 3, respectively.
The first pack usually does not exist separately at all. It's just that there is a version of Windows XP service pack 1, or Windows XP Service pack 2. The second version contains updates (updates) of various programs, possibly antivirus databases.
The very first and cheapest software project serves to get money and sell more efficient projects in the future.