Sort the major operating systems into those used on PCs and servers and those used on smartphones.
Identify an OS from the combination of its developer and the devices it ships on.
Trace the family of operating systems descended from UNIX, and pick out the OSS operating systems whose source code is public and may be modified and redistributed.
Windows is an operating system for PCs, developed and sold by Microsoft.
It adopted a GUI early on, letting users work with several windows on screen using a mouse, and it is widely used both at home and at work. Because it runs on PCs built by many different companies rather than a single maker, a large range of applications and peripherals support it.
AnalogyIt is like a car navigation unit built to a common standard that fits cars from any maker, so compatible parts and map software are easy to find.
How to rememberThe name is simply the plural of "window," taken from the way you stack several windows on the screen.
Exam points
Mix-upWindows runs on PCs from many manufacturers, while Mac OS runs only on Apple's Mac. Both are for PCs; what separates them is the range of hardware they run on.
Mac OS is the operating system Apple develops for its own Mac computers.
Because the same company designs both the OS and the hardware, the two fit together closely, and it is popular in design and video production. Current versions are written macOS, and its core follows the UNIX design tradition.
AnalogyIt is like a house whose furniture and interior were all made by one workshop, so every room feels consistent to use.
How to rememberMac is short for Macintosh, named after the McIntosh apple, which ties it neatly to the company name Apple.
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Mix-upMac OS is a PC operating system with a UNIX-family core, and it is a separate product from iOS, the same company's OS for smartphones.
Chrome OS is a lightweight PC operating system from Google that is used mainly through a web browser.
It is designed on the assumption that work such as writing documents and email happens through online services, and data is stored mainly in the cloud. Laptops running it are called Chromebooks, and their fast startup and low prices have made them popular in schools. Its core is based on Linux.
AnalogyIt is like a members-only workspace you can visit empty-handed: the tools and papers stay in the building, and you carry only the key.
How to rememberIt shares the name Chrome with Google's browser, which tells you the browser is the star of this OS.
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Mix-upChrome OS keeps little software on the device and assumes you will use online services instead. Ordinary PC operating systems have you install applications on the machine itself, so the difference lies in where the work happens.
UNIX is an OS born at AT&T Bell Labs in the late 1960s that can serve many users and run many processes at the same time.
UNIX (the origin)
Linux (compatible OS modeled on UNIX)
Android (built on Linux)
Chrome OS (built on Linux)
Mac OS (UNIX-family core)
iOS (same core as Mac OS)
It offered multi-user operation, where many people share one computer at once, and multitasking, where several programs run in parallel, from an early stage, so it has long been used on servers and workstations that need stability. Its design ideas were carried into many later operating systems, and both Linux and Mac OS belong to this line.
AnalogyIt is like the original shop of an old restaurant whose recipes were passed on to many branches, so you can taste its methods without visiting the first shop.
How to rememberAn earlier, larger OS project was called Multics, from "multi"; UNIX swapped that for "uni" as a pun, and the name stuck.
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Mix-upThe name UNIX often refers less to a single product than to a family of operating systems that share the same design ideas. Calling an OS "UNIX-like" or part of the UNIX family means it belongs to this line.
Linux is an open-source OS written from scratch on the model of UNIX, with its source code made public.
In 1991 Linus Torvalds released its core, the kernel, and developers around the world have improved it ever since. A package that bundles the kernel with the software it needs is called a distribution, and many kinds exist for different purposes. Many distributions are available free of charge, and it is widely used on web servers and other servers as well as in embedded devices.
AnalogyIt is like a public cookbook that anyone can read and add to: it takes an old restaurant's flavors as a model, and each shop circulates its own adjusted version.
How to rememberThe name blends its creator's first name, Linus, with UNIX, so the name itself shows it belongs with UNIX.
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Mix-upLinux is a compatible OS that behaves like UNIX, but it was newly written rather than built from UNIX's own program code.
UNIX vs. Linux
Aspect
UNIX
Linux
Key differenceOrigin
The original, born at a research lab in the late 1960s
A compatible OS written from scratch on the UNIX model
Source code
Varies by product
Public, and may be modified and redistributed (open source)
Main uses
Servers and workstations
Servers, embedded devices, and the base of Android and others
iOS is the mobile OS that Apple develops for its own iPhone smartphones.
It was designed around touch operation, where you control the screen with your fingers, and apps are, as a rule, obtained from Apple's App Store. It ships only on Apple devices, and its source code is not public. Its core comes from the same design as Mac OS, and the version for the iPad is now called iPadOS.
AnalogyIt is like a shopping mall where one company manages both the building and the floor space, and only shops that pass its review can move in.
How to rememberIt started out as iPhone OS and was later renamed iOS, keeping the "i" from iPhone.
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Mix-upiOS is developed by Apple and installed only on its own devices, and its source code is not published. What separates it from Android, the other major mobile OS, is whether it is OSS that may be modified and redistributed.
Android is a mobile OS built on Linux, with development led by Google.
Because its source code is public and may be modified and redistributed, many manufacturers build it into the smartphones they sell. Devices running it span a wide range of models and prices, and it is the most widely used smartphone OS in the world.
AnalogyIt is like many carmakers sharing one common chassis and each putting their own body on top before selling the car.
How to rememberIn English, "android" means a humanoid robot, which is what the green robot logo depicts.
Exam points
ExamAndroid is an OSS mobile OS whose source code (ソースコード) is public, so manufacturers can modify it and install it on their own devices.