The CME listed the E-mini S&P in 1997 at one-fifth the size of the big S&P pit contract, specifically for screen trading. It worked so well that the E-mini became the main contract and the full-size one was eventually delisted.
The same pattern repeated with micro-futures in 2019, which are one-tenth of the E-minis. Each step down widened access without changing the underlying market.
Example: the old big S&P was $250 x the index. ES is $50 x, MES is $5 x. At 5,000 index points that is $1.25 million, $250,000 and $25,000 of notional-value per contract.
Related: micro-futures, es, nq, contract-multiplier, globex