Before you jump to a conclusion I want to stress the question is about cash index. I just stumbled upon this page: http://www.cmegroup.com/trading/equity-index/settlement.html Which says: "On typical days, CME Group begins disseminating index values immediately at 8:30 a.m. Central Time (CT). " Does this mean CME have their own SP500 calculation? Does this mean they stream it to the users? If I am not being crazy and the answers are yes/yes... then what data feed re-sells it? (I was always under impressing that someone 'authorized' by S&P desseminates an 'official' version of it with frequency like 1 tick per 15 sec)...
CME has had S&P 500 cash index with symbol INX since 1982. CBOE's SPX started with S&P 500 options in 1983. It is also calculated by different vendors.