Predicting whether a server with one fast processor would be faster than a server with two slower processors is impossible without first examining the server's workload. Last week, I noted that in many cases, the cost difference between a dual-processor server and a single-processor server, both with identical clock speeds, is insignificant compared to the cost of doing a full performance audit.

However, Andrew Zanevsky, a Chicago-based SQL Server consultant, raised another important factor to consider when selecting a server: SQL Server licensing costs. "If you use the per-CPU model, you pay $5000—with a corporate discount, if you're lucky—per additional processor," Zanevsky says. "That's more expensive than the CPU itself."

Zanevsky explains that the real hit comes when you cross the 4-CPU threshold. "SQL Server Standard Edition supports up to four processors," he notes. "If you want more, you have to pay for SQL Server Enterprise Edition. Suddenly, per-CPU cost jumps from $5000 to $20,000. A license for a 4-CPU server costs $20,000, and it's $100,000 for a 5-CPU server. That fifth processor is a whopping $80,000! After that, each additional CPU is $20,000."

Zanevsky says the same principle applies when making decisions about RAM. "If you're happy with 2GB of RAM and 4 CPUs, you pay $5000 per CPU," he points out. "But if you want more memory, you need Enterprise Edition, and your license cost quadruples."

In the final analysis, 2-CPU hardware is substantially cheaper than servers that support more than two CPUs, Zanevsky says. So when you're deciding between one or two CPUs, go with two. But the choice to go beyond two processors is more complicated, especially when your proposed configuration requires Enterprise Edition. And that equation will likely grow murkier with the Yukon release of SQL Server, which I expect will provide some of its most important new database features only as part of the Enterprise Edition.