When Microsoft OS/2 needed another SQL implementation besides IBM's, Microsoft licensed Sybase SQL Server. It was marketed under the Microsoft brand for OS/2 and later for MS Windows NT, under a market sharing agreement where Sybase would forfeit the OS/2 market, with Microsoft agreeing not to sell it to other plaforms.
The original Microsoft SQL Server was based on Sybase SQL Server version 4.2. There were rumors that Microsoft attempted to purchase Sybase but declined due the high price. It is interesting to note that the technical difficulties experienced by Sybase in improving their database engine through versions 4.9.x through 11 were also experienced by Microsoft with their 4.2 code base. That is why Microsoft SQL server did not appear to be enterprise ready until version 6.5 or 7. An example of this issue was the page locking versus row locking feature.
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