第6章インフラストラクチャーの抽象化層：オペレーティングシステム

By the end of this section, you will be able to:

• Describe an operating system and its role in computing

• Explain the architecture of operating systems

An operating system (OS) is the core piece of software that typically manages and controls the interconnection of hardware and software on a computer. The OS is loaded upon start-up and is the key piece of software needed to operate any computerized device.

There are many operating systems (OSs), and anyone using a modern computer is using one of them. The typical OSs for computers are Windows, macOS, and Linux and for mobile devices, iOS and Android (Figure 6.2). Microsoft Windows is a popular operating system, celebrated for its ease of use and broad software compatibility. Apple Inc.’s macOS, which is the driving force behind Apple computers, ensures tight hardware-software cohesion. Linux, a freely available open-source OS, is acclaimed for its reliability, safety, and adaptability. Linux source code has over 27 million lines of C, while Windows has over 50 million lines. Linux offers a variety of versions or distributions, such as Ubuntu for ease of use, Fedora for the latest features, Debian for stability, and Kali Linux for security tasks. Each version is designed to meet specific needs, from general computing to specialized applications. All the commercial operating systems today manage security for users.

The goal of this section is to explain what an OS is. Traditionally, we think of the OS as the means by which communication between applications that the user wants to run and the computer hardware that is responsible for running them is facilitated. Applications typically do not directly manipulate the hardware; instead, they must ask the OS to do this on their behalf. One of the primary goals of the OS from an application software point of view is isolation. Isolation ensures that the multiple programs that are running concurrently on the same CPU and memory operate independently without interfering with each other’s execution or data. This maintains system stability and security. From a hardware point of view, the hardware is designed to enable programmers to write OSs and applications. In general, the OS mediates a program’s access to hardware resources such as the CPU (for computation); memory (for volatile storage) and disk, flash memory, and so on (for persistent storage); TCP/IP stacks, Wi-Fi, and Ethernet network interface cards, and so forth (for network communications); and keyboard, display, touch screen, audio, game controllers, and so on (for input/output). Isolation is what allows device manufacturers to update their hardware without requiring software developers to rewrite their programs each time.

To learn more about operating systems, read this informative article on understanding operating systems (https://openstax.org/r/76opsys) from How-To Geek.

Operating systems play a crucial role in managing and controlling access to hardware devices within computer systems, including peripherals such as keyboards, mice, hard drives, and other critical components. They act as gatekeepers, ensuring that interactions with these devices occur smoothly and securely. One of the key responsibilities of an OS is monitoring hardware access, which involves tracking and regulating which applications or users can communicate with the hardware and how they do so. This capability is vital for maintaining a system’s overall integrity and performance.

In addition to hardware monitoring, the OS is instrumental in enforcing authentication mechanisms. This means the OS helps verify that only authorized users gain access to certain devices, especially those considered sensitive. By managing user permissions and access levels, the OS can prevent unauthorized access to critical hardware resources, safeguarding against potential security breaches or data theft. This aspect of the OS is particularly important in environments where access to information and resources needs to be tightly controlled, such as in corporate or government settings.

The role of an IT administrator is to define which hardware devices are available within a company’s network and determine their sensitivity levels. This task requires a deep understanding of both the technical specifications of the hardware and the security implications of its use.

You may be wondering: How is the OS organized? How are resources shared across users? How is one user or process protected from another? Such questions relate to the characteristics or properties that are considered when designing an OS. Table 6.1 depicts various OS design questions and the properties they are associated with, such as structure, sharing, naming, protection, security, performance, availability, and reliability, among others.