SQL Server – Single Instance vs. Multiple Instances
Single Instance Pros Only one instance needs to be administered on the single machine. There is no duplication of components or processing overhead, such as having to run multiple database engines on the same computer. This means that the overall performance of a server with a single instance may be higher than a server running multiple instances. A single instance of SQL Server is capable of handling the processing growth requirements of the largest Web sites and enterprise data-processing systems,
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