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

The address space is the set of addresses generated by programs as they reference instructions and data. The memory space holds the actual main memory locations that are directly addressable for processing. The OS is responsible for managing these memory and address spaces (Figure 6.6). To enhance performance, computers use virtual memory address space to create the illusion of a large and continuous block of memory for applications and the operating system to utilize. To do so, the computer’s physical memory is used in combination with a portion of a hard drive that contains the swap file or page file. Pages containing address space information for programs are moved in and out of physical memory as necessary to ensure that there is enough physical memory to hold the pages of programs that are running at a given time.

Computer memory consists of two main types: primary and secondary memory. The initial point of access for a processor that also serves as direct storage for the CPU is called primary memory. To be executed, programs must reside in primary memory. In multiprocessor systems, primary memory can be classified into three architectures. The first, uniform memory access (UMA), employs a single memory controller and, thus, access time to any memory location is the same across all processors. The second, non-uniform memory access (NUMA), is a computer memory design that uses different memory controllers, thus its memory access time varies depending on the memory’s location relative to a processor. The third, cache-only memory architecture (COMA), uses multiple interconnected processing nodes, each equipped with a processor (i.e., a cache). This allows for the dynamic allocation of data for optimized access and performance in multiprocessor environments.

Memory that is used for long-term storage, housing the operating system, applications, and data that need to persist even when the power is off, is called secondary memory. Unlike primary memory, which is volatile and loses data during power interruptions, secondary memory is nonvolatile—meaning it retains data even during power failures—and thus it provides durability and data retention. Common examples of secondary memory include hard disk drives (HDDs) and solid-state drives (SSDs).

An OS must satisfy the policies of how much physical memory to allocate to each process and when to remove a process from memory. It must implement these policies using the following mechanisms: memory allocation and memory deallocation. Memory allocation is the process of setting aside sections of memory in a program to be used to store variables and instances of structures and classes. The memory allocation can be static memory allocation or dynamic memory allocation. Memory deallocation is the process of freeing the space corresponding to finished processes when that space is needed by the rest of the system. In addition, the OS must maintain mappings from virtual addresses to physical (i.e., page tables) and switch CPU context among address spaces.

A windowing system is an OS software component that manages the display of graphical user interfaces (GUIs) on a computer screen. An investigation into the influence of windowing systems on various industries, particularly in sectors like retail marketing, has yielded insightful perspectives on how such systems impact business practices, productivity, customer engagement, and overall operational effectiveness. Namely, it’s been found that windowing systems significantly enhance user experience, which is critical to retail marketing. By making it easier to integrate marketing messages or interruptions with other media that customers are watching, a windowing system helps retailers conduct targeted marketing over the Internet. Windowing systems also improve the overall user experience for customers viewing the integrated content.

Computers have many input and output devices such as the keyboard, mouse, display, or USB port. Some examples of OS-specific devices include file system (disk), sockets (network), and frame buffer (video). A frame buffer is a portion of random access memory (RAM) containing a bitmap that drives a video display. A big chunk of the OS kernel deals with I/O (Input/Output). The OS provides a standard interface between programs/ users and devices to communicate with them (Figure 6.7). A device driver’s routines interact directly with specific device types and related hardware to initialize the device, request I/O, and respond to interrupts or errors. An interrupt is a signal to the processor from either software or hardware that indicate events that needs immediate attention. Examples of device drivers include Ethernet card drivers, video card drivers, sound card drivers, and PCIe (Peripheral Component Interconnect Express) device drivers, which are associated with graphics cards and other peripherals. Device drivers are implemented by device manufacturers or open-source contributors and support a standard, internal interface. They can execute in the OS address space and run at high privilege.