diff --git a/.zk/notebook.db b/.zk/notebook.db
index ddddef7..38a612e 100644
Binary files a/.zk/notebook.db and b/.zk/notebook.db differ
diff --git a/zk/Processes.md b/zk/Processes.md
index 3a93e92..d859913 100644
--- a/zk/Processes.md
+++ b/zk/Processes.md
@@ -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)
diff --git a/zk/Threads.md b/zk/Threads.md
index 39407f4..0b0dc5c 100644
--- a/zk/Threads.md
+++ b/zk/Threads.md
@@ -1,18 +1,27 @@
 ---
 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