3.1 Development and Evolution of the Linux Kernel
The Linux operating system is a clone system of the UNIX operating system. It is a kind of UNIX-like operating system. It was born on October 5, 1991 (the time when it was officially announced to the public for the first time). The original author was Linus Torvalds. The birth, development and growth of the Linux operating system depend on five important pillars: UNIX operating system, Minix operating system, GNU project, POSIX standard and Internet.
1. UNIX operating system
The UNIX operating system is a time-sharing operating system developed on the DEC PDP-7 minicomputer in the summer of 1969 by Ken. Thompson and Dennis Ritchie of Bell Labs in the United States. The Linux operating system can be seen as a clone of the UNIX operating system.
2. Minix operating system
The Minix operating system is also a clone system of UNIX, which was developed in 1987 by the famous computer professor Andrew S. Tanenbaum. Linux was first developed in 1991 with reference to the Minix system.
3. GNU Project
The GNU Project and the Free Software Foundation (FSF) were founded by Richard M. Stallman in 1984. GNU is an acronym for "GNU's Not UNIX". By the early 1990s, the GNU project had developed many high-quality free software, including the emacs editing system, the bash shell program, the gcc series of compilers, the GDB debugger, and more. These softwares create a suitable environment for the development of the Linux operating system and are one of the foundations of the birth of Linux. Without the GNU software environment, Linux would be impossible. So, strictly speaking, "Linux" should be called "GNU/Linux" system.
4. POSIX standard
POSIX (Portable Operating System Interface) is a set of standards developed by IEEE and ISO/IEC. The standard is completed based on existing UNIX practices and experiences, and describes the operating system's calling service interface, which is used to ensure that the written application program can be ported in a variety of operating systems at the source code level. This standard is promoting the development of the Linux operating system towards formalization and is a beacon for Linux to move forward.
5. Internet
Without the Internet, and without the selfless dedication of countless computer hackers all over the world, Linux would have only grown up to the level of the Linux 0.13 (0.95) release. Since Linux version 0.95, many improvements and extensions to the kernel have been dominated by others, and the main task of Linus and other maintainers has become the maintenance of the kernel and deciding whether to adopt a patch.
Table 3.1 describes the transition history of important versions of the Linux operating system and the main features of each version.
Table 3.1 History and characteristics of Linux operating system versions
As can be seen from Table 3.1, the development of Linux has been developing towards supporting more CPUs, hardware architectures and external devices, supporting applications in a wider range of fields, and providing better performance. Simply put, the Linux kernel is an evolution rather than a design.
In addition to the free download of the Linux kernel itself, some manufacturers package the Linux kernel and a large number of useful software packages, middleware, desktop environments and applications, and develop Linux distributions (Distro) for desktop PCs and servers, such as Ubuntu, Red Hat, Fedora, Debian, SuSe, Gentoo, etc.
Android uses the Linux kernel, but adds a series of patches to the kernel, such as Binder, ashmem, wakelock, low memory killer, RAM_CONSOLE, etc. At present, most of these patches have entered the Linux product line.