Operating Systems (OS)

What is an Operating System

The original meaning (and still used by hardware engineering): a basic set of functions to control the hardware and manage things like task scheduling and system calls.
The modern terminology used by software developers, the collection of these functions is usually referred to as a kernel, while an operating system is expected to have a more extensive set of programs.

You may have seen the term GNU/Linux, Linux is the kernel, GNU is the toolset on top of that.

OS = kernel + drivers + software

Unix-like
- Linux
  - Android
  - ChromeOS
  - HarmonyOS (鸿蒙): https://consumer.huawei.com/en/harmonyos/
- BSD
  - Darwin: macOS, iOS, ipadOS, watchOS, tvOS. Based on XNU ("X is Not Unix"). Hybrid kernel.
  - QNX: a commercial Unix-like real-time operating system aimed primarily at the embedded systems market (Used by Audi, BMW, Ford, etc). Microkernel. Acquired by BlackBerry in 2010.
Windows
Fuchsia:
- https://fuchsia.dev/
- already on Next Hub, to be on Next Hub Max

Microkernel provides the most basic functionalities: low-level address space management, thread management, IPC, etc.
Device drivers, file systems, protocol stacks are included in Monolithic kernels, but are NOT in Microkernels, instead they run in user mode.

Examples:

Linux is Monolithic.
Google's Fuchsia, is based on a microkernel named Zircon. Fuchsia is NOT Linux.

Tanenbaum, the creator of Minix, arguing that microkernels are superior to monolithic kernels: