popular operating systems are Windows, Linux, Mac OS X, Android, iOS, and Windows Phone. Some are designed to work on computers and laptops (Windows, Linux, or Mac OS X), while others are designed to work on mobile devices like smartphones and tablets (Android, iOS, Windows Phone).
Operating systems have many characteristics that allow them to be classified in multiple ways. The most important characteristics are these:
■ Modern operating systems are real-time.
They execute applications and commands in real time. The benefit of being real-time is that the operating system delivers a quick and predictable response to the commands issued by the user or by the applications they are using.
■ Modern operating systems are multitasking.
They allow multiple applications to run at the same time. Hardware resources are allocated and managed automatically by the operating system and shared among all the programs and services that are running.
■ Operating systems can be multiuser or single-user.
For example, Windows and other operating systems that are designed to run on computers are multiuser. This means that you can create multiple user accounts on the same computer and have them share that computer's hardware and software resources. Single-user operating systems allow only one user account. Generally, these operating systems are found on mobile devices like smartphones and tablets. However, even these types of devices will have multiuser operating systems in the future.
■ Some operating systems can be embedded.
This means that they are designed to be used in small devices like cash registers, ATMs, and so on. These devices are very compact and have limited resources. Embedded operating systems are optimized to run on limited hardware resources, and they generally provide a small and specialized set of services and interactions.
How Do They All Work Together?
When you start a computer or a device like your smartphone, the operating system loads first. Once that is loaded, you will interact with both the application software that is installed on it and the operating system. For example, when you use an application like Microsoft Word to write a document, the application sends your input and commands to the operating system. The operating system then communicates with the hardware, and it automatically manages the resources used by Microsoft Word in order to deliver the desired results.
Users can also work directly with the operating system. For example, in Windows, you can access the files and folders that are stored on your computer and open them. You can also browse the storage on your computer, using the operating system and its features, without needing to install other applications.
Figure 1.1, which shows how the operating system and system software are layered on a typical computer, should help you understand this more clearly. The arrows indicate how the information flows.
FIGURE 1.1 The flow of information among the user, software applications, the operating system, and the hardware
Which Computer Operating System Is Best?
There is a never-ending debate about which is the best operating system for your computer. Is it Windows? Is it Mac OS X? Is it Linux? The truth is that modern operating systems are not that different anymore, at least not when it comes to what you can do with them. You can use any of them to write a document, deliver a presentation, play games, watch movies, surf the Internet, and so on. Very few features are unique to one operating system. The differences between them are mostly in the way the user interface works.
Choosing one operating system versus another is mostly a matter of personal preference. If you like how a Mac looks and feels, you might purchase a Mac and use Mac OS X. If you are a great believer in free software, then you might prefer to use Linux on your computer. If you want to have access to the greatest number of applications, devices, and learning resources, then you will go for Windows.
Accessing and Locking the Operating System
When you press the power button on a computer or other device, the operating system is loaded, and you're asked to sign in if you've set up a password or personal identification number (PIN). Regardless of the device, the basic idea is the same: you need to power up your computer or device, wait for the operating system to load, and then authenticate yourself in order to use it.
Let's do an exercise together in which you'll learn how to power on your computer and sign into Windows 7 (Exercise 1.1).
EXERCISE 1.1
Signing into Windows 7
1. Press the power button on your computer.
2. Wait for the operating system to start.
When that process is finished, you are shown the sign-in screen (Figure 1.2), where you can see the user accounts that exist on your computer.
3. Select your user account and then type your password.
If you have only one user account on your Windows 7 computer, you are directly prompted for your password, without having to go through this step. Also, if you have no password set for your account, then you won't be asked to type one.
4. Click the sign-in button, which is an arrow pointing to the right (Figure 1.3).
FIGURE 1.2 The Windows log-in screen showing the user accounts that exist on your computer
FIGURE 1.3 The sign-in screen for your user account
Once you log into Windows 7, you can start using the software applications that are installed on it and do your work. When you have finished working on the computer, you can do the following:
Switch User You can switch to another user account that exists on your computer so that someone else can use it. When you do this, your account remains active in the background and so do all your running applications. They will be available to you in the state in which you left them when you switch back to your user account. Be aware that other users can turn off the computer, and your unsaved work will be lost if that happens.
Log Off All your applications and files are closed. The computer and the operating system remain turned on, and other users can log in with their accounts and continue using the computer.
Lock Your user account remains active in the background as well all your running applications. Windows 7 displays the sign-in screen and requests your user account password. You can unlock your account by typing your password, and you will be able to resume your work exactly where you left off. No one else can use your account and your running applications unless they type
