After you plan the general structure of your organization, you can plan your servers. The number of servers you need depends on the number of users in a site and the services that you plan to provide to those users.
Depending on your needs and resources, you are likely to have decided whether to concentrate your services on just a few powerful servers or instead to distribute the services among a larger number of less powerful servers. What is important is that you make a plan. After you make that plan, you can begin to estimate the hardware requirements for your servers.
When estimating the performance of an Exchange server, consider four distinct categories of hardware: disk, processor, memory, and network. The sections that follow ...