What's the correct ratio of Exchange Server 2000 servers to Global Catalog (GC) servers?

Microsoft recommends a per-processor formula to calculate the ratio of Exchange 2000 servers to GC servers. For every four CPUs running Exchange 2000, you need one CPU for a GC server. This formula might seem odd because we're all conditioned to think of calculating Exchange servers, not processors. However, Microsoft's recommendations are based on performance data that Compaq gathered from customers. You'll probably want to have more than one GC server available because Exchange depends on having a GC available at all times for proper operation. For best performance, each Exchange server should have a GC server in close network proximity.