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Software that runs on a computing device and manages the hardware and software components that make up the system.

Task of an OS:

Provide a user interface, receiving and executing commands and requests from users.
Load, manage and execute software.
Manage computer’s hardware resources (CPU, disk drives).

Users today have a choice between three major OSes:

Only Microsoft Windows is based on proprietary code that is not Unix based.

Role: Accessed by one user directly (desktop) or many users remotely (server)?
Function: Does it need to run specific software? What is the skill set of users?
Life Cycle: What is the service lifetime? OS types have different release cycles and maintenance cycles for support and updates.
Stability: Are OS releases beta (not tested “in the wild”) or stable (tested)?
Compatibility: Is it backwards compatible as in is it compatible with software made for earlier versions?
Cost: Important factor for new systems.
- Microsoft has annual license fees.
- Apple does not charge annual fees but only works on Apple hardware.
- There are multiple Linux providers who offer enterprise support and although the software is free, support is not.

Offers desktop and server versions
Slow release cycle (3-5 years), long maintenance cycle
Emphasis on backward compatibility
Runs Graphical User Interface (GUI)
Improved scripting and management abilities are being developed to compete with Linux

Runs solely on Apple hardware
Server version adds packages to the desktop version to aid in management and sharing
UNIX certified
New major releases every 18-24 months

Unique in that after choosing Linux, you must choose a distribution
Different distributions focus on different use cases (e.g., desktop, server, scientific, network)
Some distributions offer commercial support, most is volunteer based

Linux decision points:

Role: Distributions available for variety of systems; commercial for servers and desktop, specialised to repurposing computers, embedded systems, etc.
Function: Distributions can be chosen based on purpose of usage or security needed.
Life Cycle: Most distributions have major and minor update cycles. Some Linux releases have long-term support (LTS) (5+ years, 13 years for SUSE LTS).
Stability: Some distributions offer stable, testing, and unstable releases.
Compatibility: Distributions are zero cost. Depending on need, paying for support may be worthwhile. Enterprise users can pay for support or attempt self-support.

Focuses on server applications like web and file serving.
Releases Red Hat Enterprise Linux (RHEL), a stable distribution with long release cycles.
Sponsors the Fedora Project, a personal desktop with latest software.
CentOS is a free version of RHEL software which does not offer support.
Scientific Linux is a specific use distribution based on Red Hat.

One of the first distributions
Originally derived from Slackware
Contains proprietary code and is sold as a server product. Some modules or add-ons may contain proprietary code.
Sold as a server product although a Workstation version exists.
OpenSUSE is a completely open, free version with multiple desktop packages.

Community effort that promotes the use of open-source software.
Invented its own package management system (apt) based on the .deb file format.
Ubuntu is its most popular derived distribution, which has variants for desktop, server, and applications. Ubuntu also offers an LTS version.
Linux Mint is a derivative of Ubuntu with various free versions, some have license restrictions.

Raspbian is a Linux distribution designed to run on Raspberry Pi hardware.
Linux From Scratch (LFS) consists of an online book, source code, and instructions for building a custom Linux distribution. LFS can be used as a learning tool.