(Click here to view larger diagram.)
Introduction
and Operating-System Structures
The major functions of an
operating system are to control the hardware of a computer and coordinate the
use of the hardware among several applications for the use of various users.
Operating systems provide a means for the proper use of hardware, software, and
data in the operation of the computer.
There are six major components
of an operating system; process control, file management, device management,
information management, communications, and protections. Javatpoint.com
identifies eight major components, splitting file management into main memory
management and secondary storage management and adding network management,
which wouldn't necessarily pertain to standalone computers.
Process control is the
component of an operating system that starts and ends programs. If there is an
error in the process, the operating system determines what to do with the error
in order to keep the computer processing.
File management allows the
operating system to create and delete files. It allows us to open, read, write,
and close files.
Device management involves
several components of the computer. It involves the main memory, drives, and
access to files. It also includes the inputs and outputs of devices such as
keyboards, mouses, keyboards, monitors, and printers.
Information maintenance can
track the amount of time the computer accessed certain information in the
memory. It can also track when the memory was last used.
Communication involves
interprocess communication. This would involve the message passing between two
processes that are taking place. It also involves shared memory between
different processes.
Protecting gives the operating
system a means for controlling access to the computer’s resources.
Processes,
Threads, and Process Synchronization
Processes
A process is a program that is being executed. This is more
than just the code of the program. The process includes the current activity in
the program, contents in the processor’s registers, and other temporary data.
The process state could be one of five different states of
the process:
- New - When
the process is being created
- Running - When instructions
are being executed
- Waiting – When the process is
waiting for an event to occur, such as an input or output
- Ready – When the process is
waiting to be assigned to a processor
- Terminated – When the process
is finished being executed
The process block control is also referred to as the task
control block. This is where each process is represented in the operating
system. The process control block (PCB) would include the following
information:
- Process
state – One of the states mentioned above
- Program
counter – The address of the next instruction to be executed
- CPU
registers – Registers vary depending on the computer’s architecture
- CPU-scheduling
information – Process priority, pointers to scheduling queues, or other
scheduling information
- Memory-management information
– Could include values of the base and limit registers and page tables or
segment tables
- Account information – Includes
the amount of CPU and real-time used, time limits, account numbers, job or
process numbers, etc.
- I/O status information –
Includes a list of input/output devices allocated to the process, a list of
open files, etc.
Threads
A thread is a basic part of CPU usage. Threads have an ID,
a program counter, a register set, and a stack. In a real-life scenario, I can
think of a thread as a task that I would perform, such as doing laundry, making
dinner, and watching a football game. Some tasks can be performed while
performing other tasks, like the three that I listed. Modern computers are
great at multitasking. They can take on several tasks and perform them at the
same time. One single program could have multiple threads to perform. With a
single-threaded process, each of these threads would be performed one at a
time. If I were to do each of my three tasks individually. That would take six
hours or more. Modern computers perform multithreaded processes to save a lot
of time. Many threads can be performed concurrently. When one thread is waiting
on an input from the user, the other threads can continue to keep working. In a
single-threaded process, waiting on an input would really slow things down.
Critical-section problem
A critical section is a part of the code that does not
allow any other process to occur while the program is in the critical section.
The critical-section problem is designing a way that allows for processes to
work around the critical sections. A solution to this problem must have the
following requirements:
- Mutual
exclusion – If one process is executing its critical section, no other process
can execute its critical section.
- Progress –
If no processes are executing their critical section, but some processes are
ready to enter their critical section, it must be decided which process will
enter its critical section. This cannot be postponed indefinitely.
- Bounded
waiting – A bound is established to limit the number of times that other
processes are allowed to begin their critical sections after a request has been
made and before the request is granted.
CPU
Scheduling, Main Memory, and Virtual Memory
Physical memory is the memory that is stored in the hard
drive or other memory of a computer. Physical memory is your RAM. It is fast
but volatile storage. RAM usage is measured in nanoseconds, while hard drive
disk is measured in milliseconds. When the computer runs programs off the
physical memory, it takes that data into the RAM where it will use that data to
run a program.
Virtual memory is when the computer makes references to
where the data is that it will use to run a program. Virtual memory has the
illusion of being larger than the actual physical memory. Instead of copying a
lot of information into the RAM, the computer will make a reference of where
the needed data is and then use it when it is needed.
Physical memory is limited to RAM size, while virtual
memory is limited to your hard drive space. Physical memory can access the CPU,
while virtual memory cannot access the CPU.
(Click here for additional file storage diagrams that are mentioned below.)
Mass-Storage
Structure, File-System Interface & Implementation, and I/O Systems
The process files that a
computer runs and the data files that it stores are stored on different methods
of secondary storage. These include hard disks, magnetic tapes, optical disks,
and solid-state drives (SSDs). The operating system of a computer provides
logical ways of making this data convenient to use. Different operating systems
require files to have specific attributes to help identify files. These include
the name, identifier, type, location, size, protection, times, date, and user
identification. A file directory will view this information in a table, which
allows the operating system to view and organize the files in several different
ways. These attributes will be used to help a directory search for files,
create files, delete files, rename files, list directories, and traverse the
file system. Examples of different types of directories are listed below.
Single-level directories are
the simplest. All files are files of are located in one directory. This makes
the information easy to understand. Searching in a single-level directory is
faster when the file sizes are smaller. Creating, deleting, renaming, and
updating files are also easier. One limitation of a single-level directory is
that it limits the user or users to use unique names for each file. Searching
for files takes longer when the directory is larger.
Two-level directories are
similar to single-level directories, however, each user has their own user
files directory (UFD). This allows multiple users to have files with the same
name. Each UFD lists only that user’s files. The master file directory (MFD) is
above all of the UFDs. It can be searched to find each user and then their
files. Searching files is easier with this type of directory. Users in a
two-level directory are unable to share files with other users. A single user
cannot have two files with the same name.
Tree structure directories
provide many advantages and are widely used. Every file has a unique pathname.
There is a much smaller chance of having name collisions. Searching for files
in a tree structure directory is easier. Paths to each file are well laid out. In
tree directories, the same file may be saved into multiple directories, which
would make this type of directory less efficient and potentially lead to the
user having several different versions of the same file. File sharing is not
allowed in tree structure directories.
Protection
and Security
Outline the goals and principles of domain- and
language-based protection in a modern computer system and describe how an
access matrix is used to protect specific resources a process can access.
(Consider using a matrix representation to illustrate concepts.)
Goals and Principles of domain and language-based
protection:
One of the goals and principles of domain and
language-based protection is to dictate that the programs, users, and systems
are given just enough privileges to perform their tasks with need-to-know
access. If given too many privileges, accidental or malicious corruption or
loss of files can occur. A matrix, like the one below, gives programs or
domains (left column) permission to perform allowed functions on the objects (and
printer) shown in the top row.
How security is used to protect from threats:
Computers, programs, systems, and networks are vulnerable
to numerous security threats. These possible security violations include
breaches of confidentiality, integrity, and availability, as well as theft of
service and denial of service. Security measures are carried out on four levels
to protect systems: physical, human, operating system, and network. Physical
security is allowing or denying access to the actual physical equipment. Human
security involves allowing login access to systems. This involves keeping
passwords secure and private. Users must learn to identify and avoid phishing
schemes and other attempts to gain password information. Operating systems protect
themselves from accidental or purposeful security breaches. Network security
protects break-ins from outside sources. It protects our systems from trojan
horses, viruses, worms, and other security breaches aimed at stealing,
corrupting, or deleting passwords, sensitive information, and other files.
Operating systems and network security are constantly facing newer challenges
and must be updated frequently as a result.
Summary
I learned many responsibilities of operating systems in this class. I can't quite imagine which of these I would use in the future. I would imagine that if I got more into programming and took several more programming classes, I would learn much more about processes and how they would affect my programs. I think the same would hold true for dealing with the usage of physical and virtual memory while a program is running. I believe that file storage would be very important in any aspect of Information Technology that I find myself in in the future. File storage, access, and sharing are very important in any office setting that I can imagine. Everyone involved in computers has at least a small amount of responsibility when it comes to protection and security. I believe that I will learn a lot more about protection and security while I am working on my degree, and when I find a career in IT, my responsibilities could be critical to a project or organization. As I get closer to my graduation date, I would like to look back at this course and see how much more I learned about these parts of operating systems.
(Click here for my full operating system concept map.) (Click here for the drawio file.)
References
Components
of Operating System - javatpoint. (n.d.). Www.javatpoint.com.
https://www.javatpoint.com/components-of-operating-system
Protection
in OS: Domain of Protection, Association, Authentication. (2021, March 1). GeeksforGeeks.
https://www.geeksforgeeks.org/protection-in-os-domain-of-protection-association-authentication/
Silberschatz,
A., Peter Baer Galvin, & Gagne, G. (2014). Operating system concepts.
Wiley.
