Basic Operating System Concepts

Operating System

An operating system acts as an intermediary between the user of a computer and computer hardware.
The purpose of an operating system is to provide an environment in which a user can execute programs conveniently and efficiently.

Functions of Operating System

Convenience ⇒ An OS makes a computer more convenient to use.
Efficiency ⇒ An OS allows the computer system resources to be used efficiently.
Ability to Envolve ⇒ An OS should be constructed in such a way as to permit effective development, testing, and introduction of new system functions at the same time without interfering with service.
Throughput ⇒ An OS should be constructed so that it can give maximum throughput (Number of tasks per unit time).

Major Functionalities of Operating System:

Process Management
- A process is a program in execution
  - During execution a process needs certain resources such as CPU time, memory space, files and input-output devices.
- Process management module take care of creation and division of process and scheduling of system resources.
- It includes various tasks like scheduling, termination of the process.
- OS manages various tasks at a time.
- Here CPU Scheduling happens means all the tasks would be done by the many alogirthms that use for scheduling.
Memory Management
- To execute a program it must be loaded in main memory (atleast partially) together with data.
- Memory management module takes care of allocation and deallocation of the memory space.
- Refers to the management of primary memory.
- The operating system has to keep track, how much memory has been used and by whom.
- It has to decide which process needs memory space and how much.
File Management
- All computer store, retrieve and share information.
- Normally a computer store such in form in units called files.
- File management module takes care of file relative activities such as organization, storage, retrival, naming, sharing and production of files.
Device Management
- The device management controls all input-output devices it keeps track of input-output request from processes, issues command to input-output devices and issues correct data transmission to/from input-ouput device.
Security/Privacy Management
- security module protects the resources and information of a computer system against destruction and un-authorized access.
- Privacy is also provided by the Operating System by means of passwords so that unauthorized applications can't access programs or data.
- For example, Windows uses Kerberos authentication to prevent unauthorized access to data.
Command Interpretation
- This module interprets user commands and directs system resource to process the command.

The Operating system must support the following tasks. The tasks are:

Provides the facilities to create, modification of programs and data files using an editor.
Access to the compiler for translating the user program from high-level language to machine language.
Provide a loader program to move the compiled program code to the computer's memory for execution.
Provide routines that handles the details I/O programming.

I/O System Management

The module that keeps track of the status of devices is called I/O traffic controller.
Each I/O device has a device handler that resides in a separate process associated with that device.
The I/O subsystem consists of
- A memory Management component that includes buffering caching and spooling.
- A general device driver interface.

Drivers for specific hardware devices.

Assembler -
- The input to an assembler is an assembly language program. The output is an object program plus information that enables the loader to prepare the object program for execution.
Compiler -
- The High-level languages- examples are FORTRAN, COBOL, ALGOL, and PL/I are processed by compilers and interpreters.
- A compiler is a program that accepts a source program in a “high-level language “and produces a corresponding object program.
- An interpreter is a program that appears to execute a source program as if it was machine language.
- The same name (FORTRAN, COBOL, etc.) is often used to designate both a compiler and its associated language.
Loader -
- A Loader is a routine that loads an object program and prepares it for execution.
- There are various loading schemes: absolute, relocating, and direct-linking.
- In general, the loader must load, relocate and link the object program.
- The loader is a program that places it in the core.
- The loader places into memory the machine language version of the user's program and tranfers control to it.
- Since the loader program is much smaller than the assembler, those make more core available to the user's program.

Types of Operating System

Batch Operating System
Multi programming OS
Time-sharing OS
Multiprocessing OS
Distributed OS
Network OS
Real time OS
Embedded OS

Batch OS

The user of this type of OS does not interact with the computer directly.
Each user prepares his job on an offline device like punch cards and submits it to the computer operator.
There is an operator which takes similar jobs having the same requirement and group them into batch.

Advantages of BOS

Processors of the batch systems know how long the job would run when it is in queue.
Multiple users can share the batch systems.
It is easy to manage large work repeatedly in batch systems.
The idle time for the batch system is very less.

Disadvantages

The computer operators should be well known wih batch systems
Batch systems are hard to debug.
It is sometime costly.
The other jobs will have to wait for an unknown time if any job fails.
Example → IBM's, MVS

Multi programming OS

This type of Os is used to execute more than one jobs simultaneously by a single processor.
It increases CPU utilization by organizing jobs so that the CPU always has one job to execute.
Multi programming OS use the mechanism of job scheduling and CPU scheduling.

Time Sharing OS

A time sharing operating system allow many users to share the computer resources simultaneously
Timesharing refers to the allocation of computer resources and time slots to several programs simultaneously.
For example → a main frame computer that has many users logged onto it. Each user uses the resources of the main frame that is memory CPU

Multiprocess OS

Also known as parallel operating system or tightly coupled operating system.
Such operating system have more than one processor in close communication that sharing the computer bus, the clock and sometimes memory and peripheral devices.
It execute multiple jobs at the same time makes the processes faster.
It supports large physical address this piece in larger virtual address space.
If one processor fails then other processor should retrieve the interrupted process state so execution of process can continue.

Distributed OS

Distributed means data can be stored and processed on multiple locations.
distributed operating system use multiple central processors to serve multiple real-time applications.
Independent system possess their own memory unit and CPU
These are referring to is loosely the coupled system

Network OS

These systems run on a server and provide the capability to manage data, users, group, security, application and other networking function
These types of operating system allow us to access our files, security , applications and other networking function over a small private network
Popularly known as tightly Coupled system
The other computers are called client and each computer that connects to a network server must be running client software designed to request a specific service.
Example → Cyber cafe

Advantages

Highly stable centralized server.
New technologies and hardware up-gradation are easily integrated into the system.
Security concerns are handled through servers.

Disadvantages

Servers are costly.
Users has to depend on a central location for most operations.
Maintenance and updates are required regularly.

Real-time operating system

These types of operating systems serves real time systems.
The time interval required to process and respond to inputs which is very small. This time interval is known as response time.
Real time systems are used a when there are time requirements dad are very strict light missile system, air traffic control systems, robots, etc.

Processors

The processor is defined as a logic circuit or simple chip which reacts to fundamental instructions and input processes to operate the computer.
The important purposes of a processor are getting, decoding, processing, executing and writing back as feedback to the instructions of the chip.
The processor is termed as the brain of any electronic systems that incorporate into a laptop, computers, smartphones, and embedded systems.
The control unit and arithmetic logic unit are the two significant components of the processors.

Different Types of Processor

Microprocessor

The fundamental process of the system is denoted by a microprocessor incorporated in the embedded systems.
The microprocessor is a standard processor which comprises of ALU, control unit and club of registers known as control registers, status registers, and scratchpad registers.
A one or two microprocessor can be merged together to form a multiprocessor.
The input and output operations and memory are shared by the processors.

Microcontroller

The microcontroller is standard which is available in different size and packages.
The input reading and reacting to its corresponding output is the fundamental function of the basic microcontroller and so it is called as general-purpose input and output processors (GPIO).

Embedded Processor

The embedded processor is structured to control the electrical and mechanical functions.
It comprises of numerous blocks like timer, program memory, data memory, reset, power supply, data memory, interrupt controller, clock oscillator systems, interfacing circuits, specific circuits and system application ports and circuits.

Digital Signal Processor

The digital signal processor is used for filtering, measuring, compressing analogue and digital signals.
The processing of signal means that manipulation and analysis of digital signals.
This process can be made using application specified integration circuits, digital signal processor, field-programmable gate array or it can be a computer to achieve a distinct signal.

ROM Software

ROM stands for Read-Only Memory.
ROM is storage device that is used with computers and other electronic devices.
Data stored in ROM may only be read.
ROM is used for firmware updates, which means it contains the basic instructions for what needs to happen when a computer is powered on.
Firmware is also known to as BIOS, or basic input/output system.
ROM is non-volatile storage, which means the information is maintained even if the component loses power.
ROM is located on a BIOS chip which is plugged into the motherboard.
ROM is a type of memory circuitry that holds the computer's startup routine.
The ROM BIOS tells the computer how to access the hard disk, find the operating system, and load it into RAM.

Booting

Booting basically the process of starting the computer.
When the CPU is first switched on it has nothing inside the memory.
In order to start the computer, load the Operating System into the Main memory and then computer is ready to take commands from the user.

Types of booting

Cold Booting → A.K.A hard boot. When the computer is started from its initial state by pressing the power button is called cold boot. The instructions are read from the ROM and the operating system is loaded in the main memory.
Warm Booting → A.K.A warm boot. It refers to when we restart the computer. Here, the computer does not start from the initial state, when the system gets stuck sometimes it is required to restart it while it is ON. Therefore, in this condition the warm boot takes place. Restart button or CTRL + ALT + DELETE keys are used for warm boot.

Steps of Booting

The Startup → It is the first step that involves switching the power ON. It supplies electricity to the main components like BIOS and processor.
BIOS: Power on Self Test → It is an initial test performed by the BIOS. Further, the test performs an initial check on the input/output devices, computer's main memory, disk drives, etc. Moreover, if any error occurs, the system produces a beep sound.
Loading of OS → In this step, the operating system is loaded into the main memory. The operating system starts working and executes all the initial files and instructions.
System Configuration → In this step, the drivers are loaded into the main memory. Drivers are programs that help in the functioning of the peripheral devices.
User Authentication → If any password has been set up in the computer system, the system checks for user authentication. Once the user enters the login Id and password correctly the system finally starts.

Directory Structure in Operating System

A directory is a container that is used to contain folders and files. It organizes files and folders in a hierarchical manner.
There are several logical structures of a directory :

Single level directory

The single level directory is the simplest directory structure. In it, all files are contained in the same directory which makes it easy to support and understand.
A single level directory has a significal limitaion, however, when the number of files increases or when the system has more than one user, since all the files are in the same directory, they must have a unique name. If two users call their dataset test, then the unique name rule gets violated.

Advantages

Since it is a single directory, so its implementation is very easy.
If the files are smaller in size, searching will become faster.
The operations like file creation, searching, deletion, updating are very easy in such a directory structure.

Disadvantages

Searching will become time taking if the directory is large.
This can not group same type of files together.

Two-level directory

As we know that single level directory often leads to confusion of file names among different users, the solution of this problem is to create a separate directory for each user.
In the two-level directory structure, each user has their own user file directory (UFD). The UFDs have similar structures, but each lists only the files of a single user.

Adavantages

We can give full path like /User-name/directory-name/.
Different users can have the same directory as well as the file name.
Searching of files becomes easier due to pathname and user-grouping.

Disadvantages

A user is not allowed to share files with other users.
Still, it is not very scalable, two files of the same type cannot be grouped together in the same user.

Hierarchical structure directory

A hierarchical structure directory is one in which file and folder are organized in a tree like structure with multiple level of sub-directories.

Advantages

Organization → a heirarchy directory structure allows for grouping files into smaller, more managerial groups within large groups.
Security → It allows for have control over folder and files by giving permissions.
Easy to maintain → easy to keep track of what file and folder are present and to ensure that files are stored in appropriate directories.

Disadvantages

Complexity → Hierarchical directory structure can be more complex than other type of directory structure.
Limited search ability → it can be harder to search through all the files and folders.

MS-DOS Operating System

A disk operating system (DOS) is an operating system for x86 based personal computers mostly developed by Microsoft.
MS-DOS, its rebranding as IBM PC DOS, and some operating systems attempting to be compatible with MS-DOS.
Sometimes it is referred to as "DOS", which is also the generic acronym for disk operating system.
MS-DOS was the main operating system for IBM PC compatible personal computers during the 1980s.
- It was gradually superseded by operating systems offering a graphical user interface (GUI) in various graphical Microsoft Windows operating system generations.
DOS is also used to describe several similar command-line disk operating systems.
Early computers, such as the Commodore 64, Atari 800, and Apple II, all featured a disk operating system, including Commodore Business Machines DOS, Atari DOS, and Apple DOS, respectively. DOS/360 was an OS for IBM mainframes, which first appeared in 1966, but it is unrelated to the 8086-based DOS of the 1980s.

How DOS works?

When a computer is powered on, it goes through various steps called boot process. For a computer running a disk operating system in the following six steps, such as:

The read-only memory (ROM) bootstrap loader reads the Master Boot Record and passes control over to it.
The boot record loads the disk operating system into memory, and it takes control of the machine.
The computer transfers data stored on a magnetic disk to its main memory, the random access memory
It also transfers data to external devices attached to the computer, such as a computer screen or printer.
The computer provides various applications that organizes, read, and writes files on storage. The files are organized in a hierarchical structure of directories, subdirectories, and files.

A disk operating system doesn't have a graphical user interface (GUI). Its interface is character-based, so users must type commands in the command line to indicate what actions they want.

Features of DOS

MS-DOS does not offer GUI (Graphical User Interface) and doesn't accept mouse inputs.
- It is a character-based interface system where all commands are entered in the text at the command-line prompt.
A disk operating system manages files, folders and allows program loading and execution. It can control hardware devices such as disk, memory and allocate resources.
MS-DOS offers a file system to organize, read and write files to disk storage.
It is a single-user operating system and performs various taks to ensure the proper operation of systems.
It uses a 16-bit file allocation table (FAT16), and a 16-bit interface is used to define the location of the memory of each file uniquely. These identifiers are stored in a tabular format with the name File Allocation table.
MS-DOS does not support a multiuser operating system, and it is less secure and does not have concept of user roles.
- It is very lightweight due to its basic interface and limited features.

Limitations of MS-DOS

Built-in security → DOS does not have built-in security, such as file ownership and permissions.
No multiuser or multitasking → It also does not support multiuser or multitasking.
- It can only run one program at a time, but it provides direct access to the basic I/O system and underlying hardware.

Types of DOS Commands

The entire set of commands available in DOS is divided into two types

Internal Commands

Internal commands are the simplest memory resident commands, most commonly used commands and execute immediately because they are a part of file named COMMAND.COM
When we list the files of our directory the internal commands are not seen.
Once DOS is loaded, there is not need for the DOS Diskette in a drive to use these commands. E.g. DIR, COPY, MOVE, etc.
If we execute internal command, the command processor executes the command itself.

External Commands

They are separate utility programs or files stored in DOS directory.
File name with an extension of .COM, .EXE or .BAT is considered as an external command.
They are faster than internal commands because they do not look for the COMMAND.COM file and are executed directly.
It does not execute the command itself but transfers the control to the appropriate program.