While networks move the data, the systems manipulate them, thus from the data we can extract some information.
Todays understanding distinguishes among OS, Middleware (ie. databases), and Applications. Those either provide network services, or require within the client/server architecture access to the network.
Large parts of todays society and economy depends on information, which has to be derived and transmitted reliably, uncompromised effectively, and efficiently. Often, management recognizes IT to be a cost factor rather to be productive.
The ITIL framework considers that the effective production of information requires particular rules to sustain within the IT process. Only recently, the efficient operation of IT systems has been taken into account ("Green IT"). Apart from a careful System Design, this goal can only achieved with an adequate Data Design, which is still outside the scope of current Software Engineering.
My fork of the Qmail MTA
is extremely efficient and resource-safeing programmed in C.
These aspects are tought in my Software Engineering lectures at the Frankfurt University of Applied Sciences.