A process is a program in execution. It is a unit of work within the system.

🚩 CPU, memory, I/O, files
🚩 Initialization data
„ Process termination requires reclaim of any reusable resources
„ Single-threaded process has one program counter specifying location of
next instruction to execute
🚩 Process executes instructions sequentially, one at a time, until
completion
„ Multi-threaded process has one program counter per thread
„ Typically system has many processes, some user, some operating system
running concurrently on one or more CPUs
🚩 Concurrency by multiplexing the CPUs among the processes / threads.

All data in memory before and after processing
„ ❤ All instructions in memory in order to execute
„ ❤ Memory management determines what is in memory when
Optimizing CPU utilization and computer response to users
„ Memory ❤ management activities
Keeping track of which parts of memory are currently being
used and by whom
Deciding which processes (or parts thereof) and data to move
into and out of memory
Allocating ❤ and deallocating memory space as needed. :

Usually disks used to store data that does not fit in main memory or data
that must be kept for a “long” period of time.
„ 🔥 Proper management is of central importance
„ Entire speed of computer operation hinges on disk subsystem and its
algorithms
„ OS activities
Free-space management
Storage allocation
Disk scheduling
„ 🔥 Some storage need not be fast
Tertiary storage includes optical storage, magnetic tape
Still must be managed
🔥 Varies between WORM (write-once, read-many-times) and RW (readwrite)

Protection – any mechanism for controlling access of processes or
users to resources defined by the OS
„ ✏ Security – defense of the system against internal and external
attacks
✏ Huge range, including denial-of-service, worms, viruses,
identity theft, theft of service
„ ✏ Systems generally first distinguish among users, to determine who
can do what
✏ User identities (user IDs, security IDs) include name and
associated number, one per user
UserID ✏ then associated with all files, processes of that user to
determine access control
✏ Group identifier (group ID) allows set of users to be defined
and controls managed, then also associated with each
process, file
✏ Privilege escalation allows user to change to effective ID with
more rights :

A distributed operating system is a software over a collection of independent, networked, communicating, and physically separate computational nodes.

They handles jobs which are serviced by multiple CPUs. Each individual node holds a specific software subset of the global aggregate operating system.

Each subset is a composite of two distinct service provisioners. The first is a ubiquitous minimal kernel, or microkernel, that directly controls that node’s hardware.

Second is a higher-level collection of system management components that coordinate the node's individual and collaborative activities. .
The microkernel and the management components collection work together.

They support the system’s goal of integrating multiple resources and processing functionality into an efficient and stable system.

This seamless integration of individual nodes into a global system is referred to as transparency, or single system image; describing the illusion provided to users of the global system’s appearance as a single computational entity. ✅