Capacity Management (CM) from a telecommunications and IT perspective has a fairly broad meaning, sometimes overlapping some related terms. While understandable, it is unfortunate because of the confusion it causes. But no worries, as we can sort it out pretty well right here.
Capacity Management often refers to the larger context of more than the capacity of physical entities, such as CPU, memory, ports, or even routers and switches. This broad reference is both understandable and useful. It’s understandable because, once you identify as a critical resource an entity such as software, a service, a network resource, even when these entities are not physical, you create the need to manage its capacity. So related terms such as Network Performance Monitoring (NPM), Network Capacity Management (NCM), and even Application Performance Monitoring/Management (APM), all can be considered as subsets of CM. And reasonably so. In fact, the ITIL takes this approach: http://www.itlibrary.org/index.php?page=Capacity_Management.
As a result, it can be convenient to reference the entire set as all CM. But this becomes inconvenient when we need to relate to the management of just physical entities. The simplest way out of this is to just be clear, and rely on the context.
If that is not sufficient, then let’s just agree to use CM for the specific idea of the management of physical entities, which may include software if it is isolated to a physical location (not spread around as in applications and services, to be described below).
Now we can let NPM refer to the management of network performance, which can span across elements falling under CM. Likewise, NCM can refer to the management of the capacity of these network resources, which span across elements falling under CM.
Beyond that, APM can refer to the performance monitoring of applications and services spanning across the network(s) and utilizing many different CM elements.
A term I’ve not seen, which could be convenient to add, would be Application Capacity Management, which can refer to the act of managing the capacity of applications, as you should expect. I wouldn’t mind coining a couple more obvious terms: Network Reliability Management, and Application Reliability Management, for obvious reasons.
Now to achieve success with APM and NPM, often Analytics are leveraged, and this is an emerging area as well. While there are tools in existence today that do a great job at finding causes of network and application problems before a person even has a chance to investigate, many more are being created that take it to the next level. And outside the IT and Telecommunications arenas, we have the developing engineering space of Prognostics and Health Management (PHM). PHM is all about utilizing telemetry about a component or system to estimate the risk of failure. Because lack of capacity is a form of system failure, there really is no difference in the concepts of PHM and CM or NPM or APM. So while the various camps of engineering develop within their focused areas, we shall see eventual cross pollination which can lead to exceptional abilities in the IT and Telecommunications network and system analytics arena.