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--- ops102:introduction_to_operating_systems [2024/01/10 03:42] – chris
+++ ops102:introduction_to_operating_systems [2025/01/02 15:22] (current) – [A Brief History of Operating Systems] chris
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 An operating system (OS) does exactly what the name states: It is software that operates a computer system!
-Not all computers have had or required an operating system. Particularly simple computers, including the earliest models of both business computers and microcomputers, as well as very simple embedded computers, do not require an operating system. The computer embedded into a simple mass-market microwave oven, for example, only ever runs one program, does not have communications capabilities, does not multitask, and is nevery updated, and therefore has no operating system.
+Not all computers have had or required an operating system. Particularly simple computers, including the earliest models of both business computers and microcomputers, as well as very simple embedded computers, do not require an operating system. The computer embedded into a simple mass-market microwave oven, for example, only ever runs one program, does not have communications capabilities, does not multitask, and is never updated, and therefore has no operating system.
 However, virtually all contemporary computer systems, including embedded devices, are sufficiently complex that they are equipped with an operating system.
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 All of these are system resources. The operating system manages these resources to ensure that they are used effectively, and to ensure that there are no conflicts over their use.
-As requested by the user(s), or as triggered by other factors such as the time of day or operational requirements, the OS will create processes -- running copies of computer programs. Each process is allocated compute resources by being permitted to run on one or more computer cores. To run a large number of processes, the OS will switch between them, stopping one process and starting another as needed to ensure that all of the processes get a fair share of system resources (which may not always be an equal share).
+As requested by the user(s), or as triggered by other factors such as the time of day or operational requirements, the OS will create processes -- running instances of computer programs. Each process is allocated compute resources by being permitted to run on one or more computer cores. To run a large number of processes, the OS will switch between them, stopping one process and starting another as needed to ensure that all of the processes get a fair share of system resources (which may not always be an equal share).
 The operating system will allocate the available memory to processes and to the operating system's internal operations. The OS will program the system hardware to ensure that no process can overwrite memory allocated to another process.
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 ====  The Kernel  ====
-This is the heart of the operating system, the main program (or group of programs) that controls the computer. The kernel operates in a special privileged mode, which allows it to manage the resources and security settings for all other software. The kernel is loaded by the computer’s firmware (built-in software) and sets up the computer’s hardware and resources before starting the services and user interface(s) in non-privileged mode, programming the computer’s hardware to enforce the privilege level.
+This is the heart of the operating system, the main program (or group of programs) that controls the computer. The kernel operates in a special privileged mode, which allows it to manage the resources and security settings for all other software. The kernel is loaded by the computer’s firmware (built-in software) and sets up the computer’s hardware and resources before starting the services and user interface(s) in non-privileged mode, controlling the computer’s hardware to enforce the privilege level.
 ====  System Libraries  ====
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 On the other hand, a CLI is well-suited to task automation, and many tasks may require fewer steps to perform than when using a GUI. CLIs generall require much less bandwidth when used over a network, making them well-suited to remote administration tasks.
-To compare the data demands of the two types of user interfaces:
+To compare the data demands of the two types of user interfaces, consider the amount of information that needs to be sent to the display to update it:
   *  A GUI on a 1920x1080 ("full high definition") monitor displays about 6 megabytes of data (2 million pixels x 3 bytes per pixel)
-  *  A TUI on an 80x25 character terminal displays about 2 kilobytes of data (0.002 megabytes) at one time
+  *  A CLI (or TUI) on an 80x25 character terminal displays about 2 kilobytes of data (0.002 megabytes) at one time
 As an example of the strengths of each type of user interface, consider the task of croping, resizing, and changing the format of photographs:
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   *  Before the mid-1960s: A number of different manufacturers produced various computers for business. Since these machines were expensive, and because there were many different manufacturers, a relatively small number of machines of each model were produced. Very little was standardized, and data was rarely interchanged between computers. Consequently, there were many different operating systems, each with a fairly small market.
-  *  1964/1965 - MIT and partners begin the Multics Project. This project introduced many concepts that became common in later operating systems, including a heirarcical filesystem, multitasking, and interactive operation. This project continued through 2000. However, Multics was a fairly resource-intensive operating system and ran only on very specific hardare.
+  *  1964/1965 - MIT and partners begin the Multics Project. This project introduced many concepts that became common in later operating systems, including a heirarchical filesystem, multitasking, and interactive operation. This project continued through 2000. However, Multics was a fairly resource-intensive operating system and ran only on very specific hardare.
   *  1969 - Bell Labs decided to end their participation in the Multics project. Dennis Ritchie and Ken Thompson, Bell Labs employees who were familiar with the Multics project, decided to implement some of its features in a much lighter-weight operating system, which they called Unix. Unix was soon rewritten in the C language, and could be fairly easily ported to other types of computers.
   *  1970s - Unix continued to grow in popularity. Many computer vendors licensed it and adapted it to work with their computers; some of these variants included Xenix (Microsoft), AIX (IBM), Ultrix (Digital Equipment Corporation), HP/UX (HP), and many others.