Applications and Software
Layers and categories
An operating system manages hardware and provides services to applications: process and memory management, file systems, drivers, and user accounts. Applications sit on top. Know the categories: productivity (word processing, spreadsheets), collaboration (email, chat, video conferencing, shared documents), business (CRM, ERP, accounting), browsers, utilities (compression, antivirus), and vertical specialty apps. Distinguish locally installed apps from web apps, mobile apps, and virtualized or streamed apps.
Licensing
This is a reliable trap area. Perpetual licenses are bought once; subscription licenses recur; seat licenses count named users; concurrent licenses count simultaneous users; site licenses cover an organization. Open source provides source code under a license (GPL, MIT, Apache); freeware is free of charge but closed; public domain has no rights reserved; shareware is trial-then-pay. The EULA is a contract, not a technical control.
Lifecycle
Software must be installed or deployed, patched, and eventually retired. End-of-life and end-of-support dates matter: unsupported software is a security risk even if it still runs. Compatibility checks (OS version, architecture, dependencies) prevent failed deployments, and patch management balances security against change risk.
Worked example
A 40-person firm needs email and office apps with minimal administration. A SaaS subscription for both is the fit; 40 perpetual seats plus an on-premises mail server is heavier and costlier to run.
Traps
- 'Free' does not mean open source.
- Concurrent licensing counts simultaneous users, not headcount.
- Application updates and OS updates are separate processes.