OS midterms

Operating System

• Is a collection of software that manages computer hardware resources and provides common services for computer programs

• It is a program that acts as an interface between the user and the computer hardware and controls the execution of all kinds of programs.

Resource manager view and Extended-machine view

Two viewpoints of the operating system

Resource Manager view

• The operating system’s job is to manage the different parts of the system efficiently

Extended-machine View

• The job of the system is to provide users with abstractions that are more convenient to use the actual machine.

Primary goal

• To provide a user-friendly and convenient environment to the users

Secondary goal

• Efficiency

• the operating system should perform all the management of resources in such a way that all the resources are fully utilized, and no resource should be held idle if some request to that resource is there at that instant of time

Memory management

• Refers to the management of primary or main memory

Main Memory

• A large array of words or bytes where each word or byte has its own address.

• It provides a fast storage that can be accessed directly by the CPU

Processor Management

• The OS keeps track of the processor and status of process

• Allocates the processor to a process

• De-allocates processor when a process is no longer needed

Process scheduling

• It is when the OS decides which process gets the processor , when and for how much time.

Device management

• The OS manages device communication via their respective drivers

File management

• The OS keeps track of the information, location, uses, status of the file.

File system

• Is normally organized into directories for easy navigation and usage

• These directories may contain files and other directions

Security

• This is by means of password and similar other techniques

• It prevents unauthorized access to programs and data 

Control over system performance

• Recording delays between request for a service and response from the system

Job accounting

• Keeping track of time and resources used by various jobs and users

Error detecting aids

• Production of dumps, traces, error messages, and other debugging and error detecting aids

Coordination between other software and users

• Refers to the coordination and assignment of compilers, interpreters, assemblers, and other software to the various users of the computer systems

Batch Operating System

• This type of operating system does not interact with computer directly.

• There is an operator which takes similar jobs having the same requirement and group them into batches.

Time-sharing Operating system

• This system is also known as “Multitasking System“

• This type of Operating system give each tasks some time to execute, so that all the tasks work smoothly.

• Each user gets time of CPU as they use a single system.

Quantum

• It refers to the time each task gets to execute 

Distributed Operating system

• It uses multiple central processors to serve multiple real time applications and multiple users.

• Data processing jobs are distributed among the processors accordingly

• Processors communicate with one another through various communication lines and are referred to as loosely coupled systems

Network Operating System

• It is an operating system that runs on a server and provides the server the capacity to manage data, users, groups, security, applications, and other networking functions

• The primary purpose of this system is to allow shared file and printer access among multiple computers in a network, typically a LAN, private network, or to other networks

Real Time Operating system

• A data processing system in which time interval required to process and respond to inputs is so small that it controls the environment

Response time

• The time taken by the system to respond to an input and display of required updated information

Hard real-time systems and soft real-time system

two types of real-time OS

Hard real-time systems

• They guarantee that critical tasks are complete on time.

• In this kind of system, secondary storage is limited or missing, and the data is stored in ROM

Soft real-time systems

• These are less restrictive and critical real-time tasks get priority over other tasks and retains the priority until it completes.

• These systems have limited utility than the other kind of real-time system

First Generation (1945-1955)

• Uses Vacuum tubes and Plugboards

• It is when electronic computers where created without any operating systems

• All programming was done in absolute machine language, often by wiring up plugboards to control the machine’s basic functions

• Computers around this time are used to solve simple math equations

Second Generation (1955-1965)

• Transistors and Batch systems

• During this time, the first operating system was made by General Motors for IBM 701 and it was called “GMOS“

• Operating system in during this time were called single-stream batch operating systems because the data was submitted in groups.

• Mainframe computers were introduced and were only used by professionals because of their high price tag

• typical operating during this time were FMS (Fortran Monitor System) and IBMSYS.

Third Generation (1965-1980)

• Integrated Circuits and Multiprogramming

• Multiprogramming systems were developed which allowed computers to perform multiple jobs at the same time

• The growth of minicomputers also started around this time starting with the DEC PDP-1

• These microcomputers help create a new industry and the development of more PDP which helped lead to the creation of personal computers

Fourth Generation (1980-Present)

• Personal computers were introduced during this time

• Microsoft and Windows OS was created during this time and went to become the largest operating system used in technology today

• Apple’s Macintosh was created during this time too which had a huge success due to the fact that it was so user friendly 

• Window’s development throughout the years were influenced by Macintosh and it created a strong competition between the two companies

Fifth Generation (1990-Present)

• This generation saw the rise of mobile computers and the production of microprocessors with ten million electric components

• This generation is also based on parallel processing hardware and AI software.

• High level language like C and C++, Java, .Net, etc., are used in this generation

Hardware, Operating System, Application programs, Users

4 components of a computer system

Hardware

• Provides basic computing resources

• examples are CPU, memory, I/O devices

Operating system

• Responsible for controlling and coordinating hardware with various applications and users.

• Provides the means for proper used of the resources in the operation of the computer system.

Application programs

• Define the ways in which the system resources are used to solve  the computing problems of the users 

Users

• The people, machine or other computers who uses the computer

Processor, Main memory, I/O modules, System Bus

Basic Elements of a Computer

Processor

• Controls the operation of the computer and performs its data processing functions.

Main memory

• Stores data and programs

• Typically volatile, which means the contents is lost when the computer shuts down

I/O Modules

• Moves data between the computer and its external environment 

• External environment consists of a variety of devices including secondary memory devices, communications equipment, and terminals

System bus

• Provides for communication among processors, main memory, and I/O modules

Bootstrap Program

• It is loaded at power-up or reboot 

• Typically stored in ROM or EPROM, generally known as Firmware

• It initializes all aspects of the system

• loads operating system kernel and starts execution

Exceptions

• Synchronous interrupts and are generated by the CPU

Interrupts

• Asynchronous Interrupts and are generated by other hardware devices

Trap

• Software generated interruption brought upon an error while a program is executing.

• It is also called exception handling such as divide by zero, segmentation faults, page faults, and system calls.

Program, Timer, I/O, Hardware

Classes of Interruptions

Program Interruption

• Generated by some condition that occurs as a result of an instruction execution, such as arithmetic overflow, division by zero, attempt to execute an illegal machine instruction, and reference outside a user’s allowed memory space

Timer Interruption

• Generated by a timer within the processor

• This allow the operating system to perform certain functions on a regular basis

I/O interruption

• Generated by an I/O controller, to signal normal completion of an operation or to signal a variety of error conditions

Hardware Interruption

• Generated by a failure, such as power failure or memory parity error

I/O stucture

• It refers to how the operating system manages, controls, and communicates with all the I/O devices that the users use

Ports

• A connection point used by peripheral devices to communicate with the machines.

bus

• Collection of wires and a firmly defined protocol which specifies a set of messages that can be sent on the wires

Status register, data-in register, data-out register, control register

4 registers of the I/O port

Data-in register

• Is read by the host for getting input

Data-out register

• It is written by the host for sending output

Status register

• It holds bit that can be read by the host

• It also shows the current status of the device

Control Register

• It is written by the host for starting a command or for changing the mode of any device

Primary Storage Devices

• Also known as the main memory and is the memory directly accessible by the CPU

Read Only Memory

• This memory cannot be changed, it can only be read as required

• It is used by data and programs that are frequently required and seldom changed like the system boot program

Random Access Memory

• It is volatile so that data stored to it is lost when the computer turns off

• Major form of the memory as it is quite fast but also quite expensive

Cache

• It is used to store data and instructions that are frequently required by the CPU so it doesn’t have to search for them in the main memory

Secondary Storage Devices

• It is not directly accessible by the CPU

• The data from this storage needs to be brought into the primary storage before the CPU can use it 

• Contains a large amount of data permanently

Hard disks

• They are round, flat pieces of metal covered with magnetic oxide

• Mostly famously used secondary storage devices

Floppy Disks

• They are flexible plastic discs which can bend, coated with magnetic oxide and are covered with a plastic cover to provide protection,

Memory card

• This has similar functionality to a flash drive but is in a card shape

• It can easily plug into a port and removed after its work is done

Flash Drive

• It helps in easy transportation of data from one system to another and is quite compact and comes with various features and designs

• It is also known as pen drive

CD-ROM

• Is a shiny metal disk of silver color that works like a ROM

Bit

• Smallest unit of memory space

Byte

• It is 8 bits and in some computers, it is the smallest convenient chunk of storage

Word

• It is the given native unit of data of computer architectures.

• It is made up of one or more bytes

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

Dual-mode Operation, I/O protection, Memory Protection, CPU protection

4 types of Hardware Protections

Dual-mode Operation

• The purpose of this is to protect the system from user errors or malicious programs

• The CPU operates in two modes: the User mode and the monitor mode

• Mode bit is added to the computer hardware to indicate the current mode

I/O protection

• All I/O instructions are privileged instructions to ensure that a user program could never gain control of the computer in monitor mode 

Memory Protection

• The purpose of this is to prevent a program from accessing memory that doesn’t belong to it.

• It uses two registers to determine the range of legal addresses a program may access: Base Register and Limit Register.

Base Register

• Holds the smallest legal physical memory address

Limit register

• Contains the size of the range memory outside the defined range

CPU protection

• This ensures that the CPU cannot be monopolizes by one program

• Uses a timer the decrements every clock tick and generates an interrupt when it hits 0.

Timer

• Interrupts computer after specialized period to ensure operating system maintains control

Process

• It is a program in execution

Text section

• It is the program code and also includes the current activity, as represented by the value of the program counter and the contents of the processor’s register

Process stack

• It contains temporary data such as function parameters, return addresses, and local variables

Data section

• Contains global variables

Heap

• it is the memory that is dynamically allocated during process run time.

New, Running, Waiting, Ready, Terminated

Process states

New

• The state of the process when it is being created

Running

• The state of the process when the instructions are being executed

Waiting

• The state of the process when it is waiting for some event to occur such as I/O completion or reception of signal

Ready

• It is when the process is waiting to be assigned to a processor

Terminated

• It is when the process has finished execution

Process Control Block

• It contains many pieces of information associated with a specific process including process states, program counter, CPU registers, CPU scheduling Information, and memory management information.

Program Counter

• Indicates the address of the next instruction to be executed for this process

CPU registers

• Vary in number and type, depending on the computer architecture

• They include accumulators, index registers, stack pointers, and general purpose registers, any condition-code information, and the program counter

• State information must be saved when an interrupt occurs to allow the process to be continued correctly afterward

CPU-scheduling Information

• This information includes a process priority, pointers to scheduling queues, and any other scheduling parameters

Memory-Management Information

• This information may include such items as the value of the base and limit registers and the page tables or segment tables depending on the memory system used by the operating system 

Accounting Information

• This information includes the amount of CPU and real time used, time limits, account numbers, job or process number