System software vs. application software: Which of the following is not an applications (end-user) software category?

Introduction / Context:
Differentiating system software from application software is foundational in computer science. Applications solve user tasks; system software manages and abstracts hardware and provides services for applications.

Given Data / Assumptions:

• Word processors, spreadsheets, and DTP tools are classic end-user applications.
• UNIX is an operating system (system software), not an application.
• The question asks for the item that is not applications software.

Concept / Approach:
Applications are programs designed for users (document creation, calculations, publishing). Operating systems like UNIX (and Linux, Windows, macOS) are system software: they manage processes, memory, filesystems, and devices, enabling applications to run.

Step-by-Step Solution:

Verification / Alternative check:
Vendor and academic definitions consistently place operating systems under system software; application suites depend on the OS to execute.

Why Other Options Are Wrong:
Word processing, spreadsheets, and DTP are definitive examples of applications used for productivity.

Common Pitfalls:
Confusing terminal programs or shells with the OS; mistaking a distribution’s bundled apps for the OS itself.

Final Answer:
UNIX