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zk/Processes.md
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@ -9,7 +9,8 @@ created: Friday, June 21, 2024
Programs are sequences of machine instructions stored in a file. However they do
not work by themselves. Something needs to load the file's intructions into
memory and direct the CPU to run the program. The OS does this via processes.
memory, direct the CPU to run the program and manage it during runtime. The OS
does this via processes.
A process **is a running instance of a given program**. It can be thought of as
a container in which a program runs. This container includes:
@ -18,9 +19,9 @@ a container in which a program runs. This container includes:
- a memory address
- other information about the state of the process
Other than the `init` process started by the kernel (PID1), every process has a
parent process that started it. This parent-child relationship creates a tree of
processes.
Other than the `init` process started by the kernel (PID1) (see
![systemd](systemd.md)), every process has a parent process that started it.
This parent-child relationship creates a tree of processes.
It is possible that a parent process will terminate before one of its child
processes. In this instance the child becomes an orphan. When this occurs in
@ -44,8 +45,13 @@ For instance here, `terminator` is a child of `init`, as are `zsh` and `tmux`
but they are also children of `terminator`.`pstree` is a child of `zsh` and
therefore also a child (grandchild) of `terminator`.
Each process has a unique identifier called a _process identifier_, a
_processID_ or just _PID_.
## Related notes
![systemd](./systemd.md)
![ps](./ps.md)
![Monitoring processes and resources](Monitoring_processes_and_resources.md)

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zk/Threads.md
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---
id: zadl
title: Threads
tags: []
tags: [operating-systems]
created: Wednesday, June 26, 2024
---
# Threads
A process is a running instance of a given program. A program runs sequentially
handling one task at a time, however we may need to run certain tasks in
parallel.
A ![process](Processes.md) is a running instance of a given program. A program
runs sequentially handling one task at a time, however we may need to run
certain tasks in parallel.
For example think of a program that is downloading a resource from the internet
and wants to update the UI at the same time to show the download process.
Think of a program that is downloading a resource from the internet and wants to
update the UI at the same time to show the download process.
If the program is strictly sequential, once the program starts the download, the
UI is neglected since the CPU time dedicated to the process must be focused
elsewhere.
We need the updating of the UI and the download to execute in parallel. This is
achieved via operating system **threads of execution**.
> A thread is a schedulable unit of execution within a process.
## Related notes