I think each company has their own Information System or IT department which determine what kind of technology infrastructure they need. For internal usually they use Local Area Network (LAN) and to communicate with the 'outside' they need Wide Area Network (WAN).
From that point, it will divide to hardware (computer, modem, printers..etc) and software (OS:Windows, Linux...Application, games..) .
Many kind of bussines and industries has integrated computer and Information and technology to their bussines activities, so..your have so many choices to computer industry.
They need someone that can solve many various problems related to computer technology

it's my two cent