What do you mean by operating system software?

Operating system software is a program like Windows, i.e. a program you must have to run a computer. Other software you choose to run is called applications software. Programs like Excel, Word or Internet Explorer are application software. Over history there have been lots of different operating systems. The first one for PCs was called DOS, later came Windows. IBM mainframe computers had three operating systems called VSE, MVS, and VM. Apple has their own operating system. Usually computers are sold with operating system software since you need it to do anything. Most application software is sold separately since you may not want to do the application. There is a disturbing trend in the computer industry to load up computers with trial application software which many people do not want. They do this because the computer manufacturer is paid by the application software vendor to do this.