How SQL Server 2005 Express Edition determines the CPU count and uses the CPUs during processing

Microsoft SQL Server 2005 Express Edition can only use one CPU, even if the computer has more than one CPU. This article discusses the following aspects of how SQL Server 2005 Express Edition uses CPUs:

• How SQL Server 2005 Express Edition determines the CPU count for licensing
• How SQL Server 2005 Express Edition uses multiple-core CPUs and Intel Hyper-Threading (HT) Technology-enabled CPUs during processing
  
  Note HT Technology is also known as simultaneous multithreading (SMT).

How SQL Server 2005 Express Edition determines the CPU count for licensing

To determine the CPU count for licensing, SQL Server 2005 Express Edition only counts the physical processor chips in the computer. For example, SQL Server 2005 Express Edition counts a single-core CPU, a dual-core CPU, or an HT Technology-enabled CPU as one CPU.

You can install SQL Server 2005 Express Edition on a computer that has more than one CPU. However, SQL Server 2005 Express Edition will only use one CPU.

How SQL Server 2005 Express Edition uses the CPUs during processing

SQL Server 2005 Express Edition recognizes the additional processors that are available on a computer that has a multiple-core CPU or an HT Technology-enabled CPU.

• On a computer that has a multiple-core CPU, SQL Server 2005 Express Edition starts a separate scheduler for each core.
• On a computer that has an HT Technology-enabled CPU, SQL Server 2005 Express Edition starts a separate scheduler for each logical processor.

For example, if you have a dual-core CPU, SQL Server 2005 Express Edition starts two separate schedulers. Both schedulers are available for SQL Server 2005 Express Edition to use. This behavior lets SQL Server 2005 Express Edition do some parallel processing within the limits of the one CPU that the product is using.

For more information about Microsoft SQL Server 2005 licensing, visit the following Microsoft Web site: The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, regarding the performance or reliability of these products.