At one time, accounting for IT was pretty straightforward. Large companies had mainframe computers, really big servers, running all their systems. The mainframe managed the network needed to move data to storage and handle all the communication between systems. Programs or jobs running on the mainframe where given account codes which where assigned to departments. Utilization was tracked by these account codes and the cost of the mainframe usage was allocated accordingly.
Jump ahead to today and the environment is much more complex. Today we have many servers, multiple ways to deliver data storage, and networks that span the globe. A system is no longer a single stream of data processing handling payroll or claims processing. Systems today are a web of servers, data, Service Oriented Architectures (SOA), and Cloud computing. Accounting for IT has become just as complex as IT itself. We no longer have one large cost base the can be allocated based on utilization. Properly accounting for IT requires putting IT in the context of the business. This is most effectively done by properly defining both Business Applications and IT Services.