CPU and memory scalability for Exchange Server 2003 and for Exchange 2000 Server

This article describes processor and memory scalability for Microsoft Exchange 2000 Server and for Microsoft Exchange Server 2003. The information in this article applies to Microsoft Windows Server 2003 and not to Microsoft Windows 2000 Server.

Processor scalability

Faster and more powerful CPUs and improvements in front-side bus speed are available in newer computers. Exchange Server can use high-performance CPUs and bus speed improvements to enhance the performance of your Exchange Server computer.

Computers that have four processors

Exchange Server can use computers that have four processors to increase performance when hyper-threading is turned on in the computer basic input/output system (BIOS). When you turn on hyper-threading on a Xeon MP-based computer that is running at 1.4 gigahertz (GHz) and faster, and that has a 400 MHz host bus, you can gain a 25 percent increase in Exchange Server performance. Computers that have four Xeon MP 1.4 GHz processors and faster, and that have a 400 MHz host bus, offer high levels of scalability relative to the cost of the computer. Microsoft recommends these computers for running Exchange 2000 or Exchange 2003.

Computers that have eight processors

Exchange Server can make full use of computers that have eight processors and that have a CPU speed of 900 MHz or less. These computers can offer as much as 75 percent more scalability compared to four-processor computers that have the same CPU speed. On computers that have eight Xeon MP 1.4 GHz processors and faster, and that have a 400 MHz host bus, other limitations are reached before high CPU utilization (such as 80 percent) is reached. Because the other limitations are reached first, Exchange Server cannot reach full CPU utilization. Microsoft recommends that you use computers that have eight processors when you run programs such as Context Indexing or antivirus scanning on the computer separate from the store process.

Computers that have more than eight processors

Exchange Server can effectively use only eight processors on a computer. For computers that have more than eight processors, use hardware partitioning to partition the computer into multiple eight-processor computers or into multiple four-processor computers. As an alternative, set the process affinity of the Store.exe process to only 8 processors.

Memory scalability

Because Exchange Server uses the /3GB switch as it scales up, the Exchange Server computer cannot efficiently use more than 4 gigabyte (GB) of RAM. Exchange Server does not support instancing, Physical Address Extension (PAE), or Address Windowing Extensions (AWE). Therefore, 4 GB of RAM is the maximum amount of memory that an Exchange Server computer can efficiently use.

AMD Dual-Core Processor Scalability

Dual-core processor technology is available in newer computers. This technology enables a system to take advantage of two processor cores and therefore more execution resources. Microsoft Exchange Server performance can increase, over 90 percent for some workloads, when you use dual-core processors. Servers that have two or more AMD Opteron 2.2 GHz dual-core processors and faster processors offer high levels of scalability relative to the cost of the computer. We recommend these processors for running Exchange 2000 or Exchange 2003.

For more information about how to optimize Windows memory for Exchange, click the following article number to view the article in the Microsoft Knowledge Base: Note After Windows Server 2003 Service Pack 1 is installed, the /nopae switch does not function correctly. For more information about the /nopae switch, click the following article number to view the article in the Microsoft Knowledge Base:

For more information about Exchange 2000 Enterprise Server Support, click the following article number to view the article in the Microsoft Knowledge Base: For more information about how to use the /3GB switch, click the following article numbers to view the articles in the Microsoft Knowledge Base: