In the enterprise space DB2 and Oracle are the two big players. DB2 on IBM hardware. Oracle made its mark on enterprise *nix hardware, e.g. Sun, HP and even IBM

In the enterprise space DB2 and Oracle are the two big players. DB2 on IBM hardware. Oracle made its mark on enterprise *nix hardware, e.g. Sun, HP and even IBM - AIX systems. Recently MS SQL Server (which is derived from Sybase) on Windows servers. In big corporations you don't get fired for buying Oracle. BTW Oracle bought Sun Microsystems because it was the most widely used hardware platform for Oracle. On that basis Oracle could be considered the king of RDBMS. But it is nothing special technically and it is very expensive to purchase and the support contracts are eye watering. Larry Ellison can afford to lavishly play at Admirals Cup on the licence income. Several years ago a package was released that allows you to run apps that expect Oracle on Postgres. Of course startups do not use Oracle. In fact few even use Windows. Why spend huge amounts of money when you can get better solutions for free? And there are so many good choices, including noSQL solutions.