(1ST TERM) COMSCI 2100 - Operating System

Operating System

The **most important software** that runs on a computer which **manages computer system** hardware and software, memory, and processes of the software.

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It is a group of programs that **allow a user to control and communicate with a computer.**

Software

Hardware

Two parts of a Computer System

Software

The **intangible** part of the computer system (e.g., programs, application).

Hardware

The **tangible** part of the computer system (e.g., physical machine and electronic).

True

**True or False**. Operating system is a ***software*** part of the computer system.

Microsoft Windows

macOS

Linux

Android

iOS

Commonly used operating systems

Memory Manager

Processor Manager

Device Manager

File Manager

Network Manager

5 Essential Managers of Operating System

Manager

It **monitors its resources continuously**. It enforces the policies that determine who gets what, when and how much. It allocates and deallocates the resource when appropriate.

Mainframe

Minicomputer

Supercomputer

Microcomputer

Server

5 History of Machine Hardware

Mainframe

It is a large machine – in size and in internal memory capacity.

IBM 360 (1964)

a classic example of an early mainframe

IBM 360 model 30

It requires an air-conditioned room about 18 feet square. Its CPU was 5 feet high and 6 feet wide. Its internal memory has 64K.

$200 000

How much did IBM 360 model 30 cost?

Minicomputer

It was developed to **meet the needs of smaller institutions.** It is smaller in size and memory capacity. It is cheaper.

Midrange Computers

Minicomputer is also iknown as _____.

Digital Equipment Corp. (early 1970)

example of minicomputer that only costs less than $18000

Supercomputer

It is a **massive machine**. It was developed primarily for government applications. It is for ***military operations*** and ***weather forecasting***. Its uses include: scientific research and customer support or product development.

Cray supercomputer

example of supercomputer that has 6 to 1000 processors

microcomputer

It is developed for **single users** in the laet 1970s. Its physical size was smaller than the minicomputers.

Microcomputers by Tandy Corporation and Apple Computer, Inc.

example of microcomputer

\- Single-user status

Microcomputer’s distinguishing characteristic

Workstations

It is the **most poweful microcomputers**. It is developed for commercial, educational, and government enterprises. It is networked together.

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It supports engineering and technical users.

Servers

These are **powerful computers that provide specialized services** to other computers on client/server networks.

Print servers

Internet servers

Mail servers

examples of servers

Batch System

Interactive

Real-time

Hybrid

Embedded

Five types/categories of Operating System

Batch systems

It dates from the earliest computers, when they relied on s**tacks of punched cards** or reels of magnetic tape for input.

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Jobs were entered by assembling the cards into a deck and running the entire deck of cards through a card reader as a group—a batch.

Throughput

the number of jobs completed in a given amount of time

Throughput

The efficiency of a batch system is measured in _________.

Interactive Systems

It gives a **faster turnaround than batch system**, but are slower than real-time systems. They were introduced to satisfy the demands of users who needed fast turnaround when debugging their programs.

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It required the development of time-sharing software. It provides **immediate feedback to the user** and response time can be measured in fractions of a second.

turnaround

the time it took for the jobs/processes to do their tasks

millisecond

fractions of a second.

Real-time systems

It is used in **time-critical environments** where reliability is key and data must be processed within a strict time limit. They must meet the deadline or risk significant consequences.

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They must be 100% responsive, 100% of the time.

Hard real-time systems

Soft real-time systems

Two Types of Real-Time Systems

Hard real-time systems

They risk **total system failure** if the predicted time deadline is missed.

Soft real-time systems

They **suffer performance degradation**, but not total system failure, as a consequence of a missed deadline.

Hybrid Systems

It is a **combination of batch and interactive**. Its users can access the system and get fast responses. It accepts and runs batch programs in the background when the interactive load is light.

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It takes **advantage of the free time** between high-demand usage of the system and low-demand times

Embedded systems

Computers placed inside other products to add features and capabilities.

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This permits the designers to **make the operating system more efficient** and **take advantage of the computer’s limited resources, such as memory**, to their maximum.

False

__**True or False**__. Each embedded system is designed to perform a set of specific programs, which are interchangeable among systems.

1940s: first generation

__**Year of OS Dev.**__ There is **no operating system**. Computers are based on **vacuum tube technology**. All instructions are performed manually. It has poor machine utilization. Computers are the size of the classrooms.

Dr. Grace Hopper

Who discovered a bug on Harvard’s Mark I in 1945?

Moth

What kind of bug is discovered on Harvard’s Mark I in 1945?

1950s: second generation

__**Year of OS Dev.**__ It focused on the **cost-effectiveness of the system**. It is developed **for government and business researchers.** Computers were expensive (IBM 360). There are **expensive time lags between CPU and I/O devices**.

Computer operators were hired to facilitate machine operation

Concept of job scheduling

Two widely adopted improvements in 1950s

Job Scheduling

It is the concept of **grouping together programs** with similar requirements. It introduced the need for **control cards.**

1960s: third generation

__**Year of OS Dev.**__ It has **faster CPUs.** Speeds caused problems when they interacted with slower I/O devices. The concept of **multiprogramming** was introduced.

multiprogramming

In 1960s, It introduced the concept of **loading many program**s at one time and sharing the attention of a single CPU.

interrupt

The most common mechanism for implementing multiprogramming was the introduction of the concept of the ___________.

Active multiprogramming

Passive multiprogramming

Two types of multiprogramming

Active multiprogramming

It occurs when the operating system i**nterrupts a job process**

Passive multiprogramming

The operating system **didn’t control the interrupt**s but **waited** for each job to end an execution sequence .

1970s

__**Year of OS Dev.**__ There are main memory physical capacity limitations (multiprogramming increased CPU usage), which was solved by **virtual memory**. The **database management software** was introduved. The **programs started using English-like words**, modular structures, and standard operations

Database management software

It organized data in an integrated manner, minimized redundancy, and simplified updating and access of data

1980s

__**Year of OS Dev.**__ **Cost/performance ratio** improvement of computer components. There are **more flexible hardware**, with logical functions built on easily replaceable circuit boards. **Firmware and Multiprocessing** were introduced.

Firmware

Introduced in 1970s, it indicates that a program is **permanently held in read-only memory (ROM)**

Multiprocessing

Introduced in 1970s, it means having more than one processor. More complex languages were designed to coordinate the activities of the **multiple processors servicing a single job.**

1990s

__**Year of OS Dev.**__ **Internet capability** sparked the proliferation of **networking capability.** The WWW made the Internet accessible. It introduced a **proliferation of multimedia applications** demanding additional power, flexibility, and device compatibility for most operating systems

Tim Berners-Lee

In 1990s, who made the WWW?

World Wide Web

Meaning of WWW

2000s

__**Year of OS Dev.**__ It supports: multimedia application, Internet and Web access, and Client/Server computing. It increased CPU speed, has high-speed network attachments, and increased number of storage devices. It introduces **virtualization.**

Object-oriented design

The way the components of the OS are programmed and organized, specifically the use of ________, and and the reorganization of the operating system’s nucleus.

kernel

It is the **operating system’s nucleus**. It is a part of the OS that **resides in memory at all times**, performs the **most essential** operating system **tasks**, and is protected by hardware from user tampering.

Early OS loaded its **entirety into main memory**.

Object-oriented OS load only **critical elements into main mamory** and **call other objects as needed.**

Difference between Early OS and Object-Oriented OS

Memory Management

It refers to how computers **manage their main memory.**

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It keeps the **resources** that the CPUs can **immediately access.**

Access Memory

Random Access Memory (RAM)

Core Memory

Primary Storage

4 Types of Memory Manager

Single-user contiguous scheme

Fixed partitions

Dynamic partitions

Relocatable dynamic partitions

4 Early Memory Allocation Schemes

Single-user Contiguous Scheme

This early moment allocation scheme requires a **minimal amount of work** done by the operating system's memory manager.

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Program was loaded in its **entirety into memory** and allocated as much **contiguous space in memory** as needed.

False

__**True or False**__. Single-user contiguous scheme permits multiprogramming.

Sequentially

In ***single-user contiguous scheme***, jobs are processed _______ in a single-user system.

Static Partitions

***Fixed partition*** is also called as _______.

Fixed Partition

This early memory allocation scheme is where the main memory is **partitioned** (equal or unequal), with **one job in each partition**.

shut down, reconfigured, and restarted

In ***fixed partition***, its sizes remain static unless and until the computer system is _______.

Protection of the job’s memory space

Matching job size with partition size

The Two Requirements of Fixed partition

True

__**True or False**__. ***Fixed partition*** permits multiprogramming.

Dynamic Partition

This early memory allocation scheme has its memory divided into **variable-sized partitions** based on the **size of the process**

First-Fit Memory Allocation

Best-Fit Memory Allocation

Two job allocation methods of Dynamic Partition

First-Fit Memory Allocation

A job allocation method of dynamic partition where the **first** partition **fits** the requirements.

Best-Fit Memory Allocation

A job allocation methods of dynamic partition where the **smallest** partition fits the requirements.

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**Internal fragmentation** is **reduced**, but not eliminated.

Speed

__**Space or Speed.**__ The major aspect of first-fit memory allocation.

Space

__**Space or Speed.**__ The major aspect of best-fit memory allocation.

Deallocation

It is the **process of freeing** an allocated memory space.

Resets the status of the memory block to “free”

Deallocation method for fixed-partition system

Case 1: Joining Two Free Blocks

Case 2: Joining Three Free Blocks

Case 3: Deallocating an Isolated Block

Deallocation method for dynamic partition system

Relocatable Dynamic Partitions

Memory Manager relocates **programs to gather together** **all of the empty blocks and compact them** to make one block of memory, large enough to accommodate some or all of the jobs waiting to get in

Garbage collection or Defragmentation

The **compaction of memory**, sometimes referred to as ___________, is performed by the operating system to reclaim fragmented sections of the memory space

Virtual Memory

A **storage method** that gives the user the impression that their **main memory is quite large**, this approach allows them to **load larger size programs than the primary memory** that is accessible.

Enhanced level of multiprogramming which will then increase CPU consumption

Effect of using virtual memory

Paging

It is a storage mechanism used to **retrieve processes.**

Pages

In paging, the main memory is divided into small blocks called ______.

Equal

It is very important to have pages and frames which are of _______ sizes which are very useful for mapping and complete utilization of memory.

Mapping

Complete utilization of memory

Pages and frames which are of equal sizes are very useful for _____ and ________.

Demand Paging

A condition occurred in the virtual memory where the pages of the processes are **stored in the secondary memory** and the page is brought to the **main memory when required**.

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It is the process of calling the pages to main memory from secondary memory upon demand

Page Replacement Algorithms

In demand paging, the pages are brought to the main memory when required by the _______.

First In First Out (FIFO) Replacement Algorithm

Least Recently Used (LRU) Replacement Algorithm

2 Page Replacement Algorithms

Page Fault

It occurs when a program tries to access a memory page that is **not present** in the memory.

Page Hit

It occurs when a program tries to access a memory page that is **already present** in the memory.

First In First Out (FIFO) Algorithm

This is the **simplest** page replacement algorithm.

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The policy is to **remove** the pages that have been in memory **the longest**.

Least Recently Used (LRU) Replacement Algorithm

In this algorithm, the page will be replaced which is **least recently used.**

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Page replacement policy swaps out the pages that show the **least amount of recent activity,** figuring that these pages are the least likely to be used again in the immediate future.