Der Kreis der Besitzer von Mikrocomputern nimmt standig zu. Nur ist es nicht mit der Anschaffung des Rechners get n. Es sind problembezogene Programme notig. Diese werden oft in BASIC formuliert, wobei fast jeder Hersteller einen eigenen Dialekt dieser Sprache anbietet. Wer effektvoll programmieren will, mug also die auf seinen Rechner ausgerichtete Variante des BASIC beherrschen. Dieses Buch wendet sich an Leser, die lernen wollen, einen Commodore-Rechner der Serien cbm 4001 oder cbm 8001 in BASIC zu programmieren. Dabei ist ein regelmagiges, aktives Arbeiten an einem entsprechenden Rechner unverzichtbar. Deshalb sollten die zahlreichen Experimente unbedingt durchgefUhrt und die Aufgaben, soweit das moglich ist, am Rechner gelost werden. Vorkenntnisse Uber Aufbau und Funktionsweise von Digitalrechnern sind nicht unbedingt erforderlich. Da die Eigenarten der Programmierung sich an mathematischen Problemen besonders einfach demonstrieren lassen, werden geringe Mathematikkenntnisse voraus gesetzt, die sich im wesentlichen auf die Grundlagen der Algebra beschranken. Zu danken habe ich meiner Frau fUr die umfassende Unterstiitzung und die Obernahme der Schreibarbeiten. Ich danke auch der GeschaftsfUhrung der BDB BUro KG, Hamburg 26, die die Entstehung dieses Buches durch die vorUbergehende Oberlassung einer cbm Rechenanlage gefOrdert hat. Nicht zuletzt gilt mein Dank den Mitarbeitern des Verlages fUr die reibungslose Zusammenarbeit. G.Oetzmann Hamburg, im FrUhjahr 1982 1 1 Was ist BASIC? Charakteristisch fur einen frei programmierbaren Digitalrechner ist die Trennung der Ar beitsanweisung (des Programms) von der ausfuhrenden Anlage. Dadurch wird es moglich, einer Anlage durch Wechsel des Programms immer wieder neue Aufgaben zu Ubertragen."

Die Benutzer von Taschenrechnern werden durch den Trend zu immer leistungsfahigeren Produkten motiviert, stets noch weiterreichende Wunsche zu aussern. Noch sind die letz- ten Roehrenfernseher und Dampfradios aus der guten Stube nicht verschwunden, da ruft mancher bereits nach der IBM 360 in der Groesse einer Streichholzschachtel und mit der Betriebszuverlassigkeit eines Radiergummis! Ganz so weit sind wir aber noch nicht. Einerseits konnte durch die Minaturisierung und die Grossserienherstellung von Bauteilen der Elektronik die Leistungsfahigkeit der Rech- ner stark anwachsen; besonders deutlich zeigte sich dies im stetigen Vergroessern des ver- fugbaren Speicherplatzes (RAM-Bereich), aber auch in den "ausgeklugelten" Programmier- moeglichkeiten, wie Speicherarithmetik, indirekte und relative Adressierung. Andererseits wurde als Folge der Miniaturisierung mit Read Only Memories (ROM) eine Verbesserung der Algorithmen erreicht, so dass die heutigen Taschen-und Kleinrechner einen derartig hohen technischen Standard besitzen, wie er vor 10 Jahren selbst von "ausgewachsenen" Tischcomputern nicht erreicht wurde. Einer dieser hochkomfortablen Rechner in Taschenformat ist der programmierbare Taschenrechner HP-41 C/CV, der durch die Kombination mit zusatzlicher Peripherie zu einem aussergewoehnlich leistungsfahigen und flexiblen Computersystem erweitert werden kann. Das einzigartige Tastenfeld des HP-41C/CV erlaubt dem Anwender, die Tasten und deren Funktionen seinen Kenntnissen und persoenlichen Erfordernissen anzupassen. Die eingegebenen Daten und Programme bleiben durch einen "Permanent-Speicher" auch nach dem Abschalten des Rechners gespeichert. UEber die Ein-/Ausgabeanschlusse (bi- direktionale Datenanschlusse) koennen Peripheriegerate (z. B. Drucker, Karten Ieser, Bar- Code-Leser), sowie Software-Module mit einer Speicherkapazitat bis 8K BYTE pro Modul angeschlossen werden.

Seit der Erfindung des Transistors hat der Mikroprozessor die wesentlichste Umstellung in der Elektrotechnik und auf den ihr benachbarten Gebieten gebracht. Der Mikroprozessor ist das Ergebnis einer stetigen Entwicklung zu immer hoeherer Integrationsdichte. Wenige, aber sehr komplexe Bausteine bilden ein Mikroprozessorsystem, mit dessen Hilfe heute Aufgaben geloest werden, fur die fruher eine Vielzahl verschiedener Bausteine noetig war. Mit der Verringerung des schaltungstechnischen Aufwandes ging eine Zunahme der Programmieraufgaben einher. Mit den entsprechenden Fachwoertern ausgedruckt: Die Problemloesung verlagerte sich von der Hardware zur Software. Diese noch andauernde Entwicklung hat zwei Folgen: Alle diejenigen, die sich bisher mit Hardware beschaftigten, mussen sich in die neue Technik einarbeiten. Fur viele bedeutet es eine betrachtliche Umstellung, sich ploetzlich mit Befehlen, Adressen, Programmen und ahnlichen Begriffen beschaftigen zu mussen. Das sehr weite Einsatzgebiet dieses neuen Bausteins bringt es ferner mit sich, dass Personen mit dieser neuen Technik konfrontiert werden, die vorher nicht oder nur in sehr geringem Umfang mit der Elektronik in Beruhrung gekommen sind. An beide ZieJgruppen wendet sich dieses Buch. Um den Mikroprozessor sinnvoll einsetzen zu koennen, genugt es nicht, ihn als black box zu betrachten. Struktur und Wirkungsweise von Mikroprozessoren werden daher in Kapitell an einem Modell erklart. Kapitel 2 gibt eine Einfuhrung in die Programmierung. Wichtige Begriffe und Arbeitsweisen auf dem Gebiet der Software werden beschrieben.

1.1 Die Formulierung von Programmen 1.1.1 Ein Betriebssystem besteht aus zahlreichen Programmen sehr unterschied- 1 icher Groesse. Nicht selten bewegt sich der Umfang eines Betriebssystems zwischen 100 Kund 500 K Bytes. Ein mittelgrosser Ubersetzer fur eine Programmiersprache umfasst dagegen nur 30 - 50 K Bytes. (K ist eine Abkurzung fur Kilo, d. h. Tau- 10 send. In der Informatik bedeutet K stets 1024=2 .) In diesem Buch studieren wir Betriebssysteme aus der Sicht des Systementwicklers. Das bedeutet, dass wir die verschiedenen Aufgaben eines Betriebssystems analysieren sowie Programme entwickeln, die diese Aufgaben erfullen. Dabei wird aber weniger die Analyse als vielmehr die Synthese im Vordergrund stehen: wir eroertern, wie die Komponenten eines Betriebssystems unter vorgegebenen Bedingungen realisiert werden koennen. Dabei kann das vorl iegende Buch als Vorbereitung fur andere Bucher dienen, welche sich mehr der Analyse von Betriebssystemen widmen. Wenn der Leser das ange- botene Material durchgearbeitet hat, wird er fur eine tiefergehende Analyse der Leistungsfahigkeit von Betriebssystemen und fur eine Beschaftigung mit Warte- schlangentheorie gut vorbereitet sein. Entwicklungsstudien bilden den angemessenen Hintergrund fur die mathematische Analyse von Systemmodellen. Die Systemanalyse bleibt daher im vorl iegenden Buch auf den Vergleich einiger alternativer Entwurfe und Implementierungen beschrankt.

Das Thema soll in einen Grenzbereich der Materialwirtschaft fuhren, der durch die tagespolitischen Ereignisse immer grossere Bedeutung fur die Unternehmung gewinnt. Naturgemass ist in einer marktorientierten Gesellschaft das verkaufs fahige Produkt da Objekt aller Anstrengungen und Leistungen. Produktion und Verkauf stehen im Blickpunkt, andere Bereiche werden als notwendig be trachtet, wahrend das Gebiet der Entsorgung innerhalb der Unternehmung zu nachst ohne besondere Beachtung bleibt. Mit zunehmender technologischer Perfektion, finanzwirtschaftlicher Beherrschung des Produktabsatzes ruckt die Guterbereitstellung zur Deckung des Bedarfs plotzlich in den Hintergrund - Schlagworte wie Konsumterror, Abfallgesell schaft u. a. kennzeichnen den Wandel - und die Frage nach der Qualitat der Produktion, nicht mehr des Produkts, gewinnt eine neue Dimension. Damit wird fur die Unternehmung die Alternative aufgezeigt, dass es nicht so sehr auf die Qualitat des Produktes ankommt, weil die Grundbedurfnisse befriedigt sind, sondern auf die Qualitat der Produktion, damit die Beeintrachtigung kleiner bleibe als der Nutzen der Bedarfsbefriedigung. Diese Uberlegungen zwingen die Unternehmung, einen Sektor ihrer Existenz sowohl in die Kosten- als auch in die Erlosbetrachtung einzubeziehen, namlich den Umweltschutz mit seinen Be reichen Luft- und Wasserbelastung, Abfallbeseitigung sowie Ruckgewinnung von Kreislaufstoffen aus der Luft, dem Wasser und den Abfallen. Eine Materialverwertung ohne Reststoffe mit einem Produktionsverfahren ohne Umweltbeeintrachtigung wird in der Zukunft keine Standortprobleme, keine negative Publizitat kennen und im Markt dadurch begunstigt sein."

Develop cloud applications based on the most popular Azure services, including hosting web applications, running containers, storing data using both relational and non-relational databases, and much more Key Features Take a modern approach to Azure Cloud development and management Get a detailed introduction to services such as web hosting, databases, and serverless platforms Get the hang of cloud services with this practical, developer-centric guide for Azure developers Book DescriptionMicrosoft Azure is currently one of the fastest growing public cloud service providers thanks to its sophisticated set of services for building fault-tolerant and scalable cloud-based applications. This second edition of Azure for Developers will take you on a journey through the various PaaS services available in Azure, including Azure App Service, Azure Functions, and Azure SQL Databases, showing you how to build a complete and reliable system with ease. Throughout the book, you'll discover ways to enhance your skills when building cloud-based solutions leveraging different SQL/NoSQL databases, serverless and messaging components, containerized solutions, and even search engines such as Azure Cognitive Search. That's not all!! The book also covers more advanced scenarios such as scalability best practices, serving static content with Azure CDN, and distributing loads with Azure Traffic Manager, Azure Application Gateway, and Azure Front Door. By the end of this Azure book, you'll be able to build modern applications on the Azure cloud using the most popular and promising technologies to make your solutions reliable, stable, and efficient. What you will learn Identify the Azure services that can help you get the results you need Implement PaaS components - Azure App Service, Azure SQL, Traffic Manager, CDN, Notification Hubs, and Azure Cognitive Search Work with serverless components Integrate applications with storage Put together messaging components (Event Hubs, Service Bus, and Azure Queue Storage) Use Application Insights to create complete monitoring solutions Secure solutions using Azure RBAC and manage identities Develop fast and scalable cloud applications Who this book is forThis book is for developers and IT professionals who want to learn Microsoft Azure by developing applications based on various cloud services. Prior knowledge of software development and the basics of software architecture and Azure services give you an advantage.

Learn how to develop modern object-oriented applications with PHP using test-driven development (TDD) and behavior-driven development (BDD) aided by mature reusable components Key Features Create clean code based on components' reusability to create large-scale enterprise applications Make effective use of design patterns in an object-oriented software Understand the division of a PHP web application structure in layers to build customized websites and apps for various business needs Book DescriptionConsidered the next generation of the Zend framework, Laminas is a high-performance PHP framework for creating powerful web applications with an evolutive architecture. This book takes a hands-on approach to equip you with the knowledge of the Laminas framework necessary to start building web applications based on the reuse of loosely coupled components. You'll learn how to create the basic structure of a PHP web application divided into layers, understand Laminas' MVC components, and be able to take advantage of the Eclipse platform as a method for developing with Laminas. Step by step, you'll build an e-commerce application based on the technical requirements of a fictional business, and get to grips with implementing those requirements using Laminas components. By the end of this web development book, you'll be able to build a completely secured MVC application in PHP language using Laminas. What you will learn Discover how object-relational mapping is implemented with laminas-db Understand behavior-driven development concepts to sharpen your skills Create lean controllers and flexible views Build complete models and reusable components Explore the Eclipse platform for developing with Laminas Find out how easy it is to generate HTML forms with laminas-form Practice test-driven development to write precise programs Who this book is forThis book is best suited for programming beginner or developers with some experience looking to create clean-coded object-oriented web applications. Knowledge of basic PHP syntax, specifically variables, control structures, and functions, will aid you in understanding the concepts covered.

If you want to build websites, understanding Bootstrap will save you a lot of time and effort. Bootstrap is a user-friendly CSS framework that allows developers to create mobile-friendly and responsive websites. Bootstrap is the most widely used framework for creating mobile-first, responsive websites. It fixes a number of issues that we experienced previously, including cross-browser compatibility. Today, webpages are optimized for all browsers (Internet Explorer, Firefox, and Chrome, to name but a few) and screen sizes (desktop, tablets, phablets, and phones). Regardless of project size, Bootstrap provides a solid foundation for any website. It includes Reboot, which is based on Normalize.css and aids with the smoothing out of browser disparities for various page elements. Bootstrap also has fantastic typography. Checkboxes, radio buttons, choose choices, and other basic HTML form elements have been restyled to give them a more modern look. Bootstrap's scope extends beyond online app design to include devices, allowing for a more seamless user experience. CSS, reusable segments, and JavaScript portions are some of its key characteristics. It has a much clearer design, JavaScript tools, and CSS, among many other capabilities that front-end developers employ. In short, when it comes to UI, the scope is enormous. Key Features: * A step-by-step approach to problem-solving and skill development * A quick run-through of the basic concepts, in the form of a "Crash Course" * An advanced, hands-on core concepts, with a focus on real-world problems * An industry-level coding paradigm, practice-oriented explanatory approach * A special emphasis on writing clean and optimized code, with additional chapters focused on coding methodology

Mastering NativeScript helps readers master the NativeScript framework for faster and more robust mobile app development. Mobile devices have progressed from a mere means of communication to becoming a critical business tool in recent years. People are increasingly glued to their smartphones as technology advances at breakneck speed. The significance of mobile app development cannot be overstated. And when it comes to mobile app development, NativeScript is a hot topic. NativeScript was introduced by Telerik, and it allows you to develop truly native apps for iOS and Android under a single code base using JavaScript or TypeScript, XML, and a subset of CSS. The charm of NativeScript is that it enables us to code once for multiple platforms (iOS 7.1 and Android 4.1), simultaneously sharing code amongst them while still allowing developers to add platform-specific instructions with flawless execution. As a result, you may release an app for both platforms using a single code base. NativeScript is comprised of three parts: a JavaScript (JS) virtual machine, a runtime, and a bridge module. The JS virtual machine is used for interpretation and execution of JavaScript code. The bridge module then converts the calls to platform-specific API calls and returns the outcome to the caller. NativeScript is a very appealing paradigm, and is rising in popularity as we speak. It can be used to construct practically any program, including communication apps (news and social networking), gaming applications (Chess, Tic-Tac-Toe, Pinball), and chat apps. It can also handle maps and geolocation apps. With Mastering NativeScript, learning NativeScript becomes straightforward, which will undoubtedly help readers advance their careers. The Mastering Computer Science series is edited by Sufyan bin Uzayr, a writer and educator with over a decade of experience in the computing field.

A complete journey to automating infrastructure provisioning and cloud-native application deployment Key Features Leverage Crossplane and Kubernetes for a unified automation experience of infrastructure and apps Build a modern self-service infrastructure platform abstracting recipes and in-house policies Clear guidance on trade-offs to manage Kubernetes configuration and ecosystem tools Book DescriptionIn the last few years, countless organizations have taken advantage of the disruptive application deployment operating model provided by Kubernetes. With Crossplane, the same benefits are coming to the world of infrastructure provisioning and management. The limitations of Infrastructure as Code with respect to drift management, role-based access control, team collaboration, and weak contract make people move towards a control-plane-based infrastructure automation, but setting it up requires a lot of know-how and effort. This book will cover a detailed journey to building a control-plane-based infrastructure automation platform with Kubernetes and Crossplane. The cloud-native landscape has an overwhelming list of configuration management tools that can make it difficult to analyze and choose. This book will guide cloud-native practitioners to select the right tools for Kubernetes configuration management that best suit the use case. You'll learn about configuration management with hands-on modules built on popular configuration management tools such as Helm, Kustomize, Argo, and KubeVela. The hands-on examples will be patterns that one can directly use in their work. By the end of this book, you'll be well-versed with building a modern infrastructure automation platform to unify application and infrastructure automation. What you will learn Understand the context of Kubernetes-based infrastructure automation Get to grips with Crossplane concepts with the help of practical examples Extend Crossplane to build a modern infrastructure automation platform Use the right configuration management tools in the Kubernetes environment Explore patterns to unify application and infrastructure automation Discover top engineering practices for infrastructure platform as a product Who this book is forThis book is for cloud architects, platform engineers, infrastructure or application operators, and Kubernetes enthusiasts who want to simplify infrastructure and application automation. A basic understanding of Kubernetes and its building blocks like Pod, Deployment, Service, and Namespace is needed before you can get started with this book.

Get up to speed with the most important concepts in driver development and focus on common embedded system requirements such as memory management, interrupt management, and locking mechanisms Key Features Write feature-rich and customized Linux device drivers for any character, SPI, and I2C device Develop a deep understanding of locking primitives, IRQ management, memory management, DMA, and so on Gain practical experience in the embedded side of Linux using GPIO, IIO, and input subsystems Book DescriptionLinux is by far the most-used kernel on embedded systems. Thanks to its subsystems, the Linux kernel supports almost all of the application fields in the industrial world. This updated second edition of Linux Device Driver Development is a comprehensive introduction to the Linux kernel world and the different subsystems that it is made of, and will be useful for embedded developers from any discipline. You'll learn how to configure, tailor, and build the Linux kernel. Filled with real-world examples, the book covers each of the most-used subsystems in the embedded domains such as GPIO, direct memory access, interrupt management, and I2C/SPI device drivers. This book will show you how Linux abstracts each device from a hardware point of view and how a device is bound to its driver(s). You'll also see how interrupts are propagated in the system as the book covers the interrupt processing mechanisms in-depth and describes every kernel structure and API involved. This new edition also addresses how not to write device drivers using user space libraries for GPIO clients, I2C, and SPI drivers. By the end of this Linux book, you'll be able to write device drivers for most of the embedded devices out there. What you will learn Download, configure, build, and tailor the Linux kernel Describe the hardware using a device tree Write feature-rich platform drivers and leverage I2C and SPI buses Get the most out of the new concurrency managed workqueue infrastructure Understand the Linux kernel timekeeping mechanism and use time-related APIs Use the regmap framework to factor the code and make it generic Offload CPU for memory copies using DMA Interact with the real world using GPIO, IIO, and input subsystems Who this book is forThis Linux OS book is for embedded system and embedded Linux enthusiasts/developers who want to get started with Linux kernel development and leverage its subsystems. Electronic hackers and hobbyists interested in Linux kernel development as well as anyone looking to interact with the platform using GPIO, IIO, and input subsystems will also find this book useful.

Create a complete continuous delivery process using modern DevOps tools such as Docker, Jenkins, Kubernetes, Ansible, Terraform, and many more Key Features Build reliable and secure applications using Docker containers Create a highly available environment to scale Jenkins and your services using Kubernetes Automate your release process end-to-end Book DescriptionThis updated third edition of Continuous Delivery with Docker and Jenkins will explain the advantages of combining Jenkins and Docker to improve the continuous integration and delivery process of app development. You'll start by setting up a Docker server and configuring Jenkins on it. Next, you'll discover steps for building applications and microservices on Dockerfiles and integrating them with Jenkins using continuous delivery processes such as continuous integration, automated acceptance testing, configuration management, and Infrastructure as Code. Moving ahead, you'll learn how to ensure quick application deployment with Docker containers, along with scaling Jenkins using Kubernetes. Later, you'll explore how to deploy applications using Docker images and test them with Jenkins. Toward the concluding chapters, the book will focus on missing parts of the CD pipeline, such as the environments and infrastructure, application versioning, and non-functional testing. By the end of this continuous integration and continuous delivery book, you'll have gained the skills you need to enhance the DevOps workflow by integrating the functionalities of Docker and Jenkins. What you will learn Grasp Docker fundamentals and dockerize applications for the CD process Understand how to use Jenkins on-premises and in the cloud Scale a pool of Docker servers using Kubernetes Write acceptance tests using Cucumber Run tests in the Docker ecosystem using Jenkins Provision your servers and infrastructure using Ansible and Terraform Publish a built Docker image to a Docker registry Deploy cycles of Jenkins pipelines using community best practices Who this book is forThe book is for DevOps engineers, system administrators, Docker professionals, or anyone who wants to explore the power of working with Docker and Jenkins together. No prior knowledge of DevOps is required to get started.

Get up and running with Kubernetes 1.19 and simplify the way you build, deploy, and maintain scalable distributed systems Key Features Design and deploy large clusters on various cloud platforms Explore containerized application deployment, debugging, and recovery with the latest Kubernetes version 1.19 Become well-versed with advanced Kubernetes topics such as traffic routing or Pod autoscaling and scheduling Book DescriptionWith its broad adoption across various industries, Kubernetes is helping engineers with the orchestration and automation of container deployments on a large scale, making it the leading container orchestration system and the most popular choice for running containerized applications. This Kubernetes book starts with an introduction to Kubernetes and containerization, covering the setup of your local development environment and the roles of the most important Kubernetes components. Along with covering the core concepts necessary to make the most of your infrastructure, this book will also help you get acquainted with the fundamentals of Kubernetes. As you advance, you'll learn how to manage Kubernetes clusters on cloud platforms, such as Amazon Web Services (AWS), Microsoft Azure, and Google Cloud Platform (GCP), and develop and deploy real-world applications in Kubernetes using practical examples. Additionally, you'll get to grips with managing microservices along with best practices. By the end of this book, you'll be equipped with battle-tested knowledge of advanced Kubernetes topics, such as scheduling of Pods and managing incoming traffic to the cluster, and be ready to work with Kubernetes on cloud platforms. What you will learn Manage containerized applications with Kubernetes Understand Kubernetes architecture and the responsibilities of each component Set up Kubernetes on Amazon Elastic Kubernetes Service, Google Kubernetes Engine, and Microsoft Azure Kubernetes Service Deploy cloud applications such as Prometheus and Elasticsearch using Helm charts Discover advanced techniques for Pod scheduling and auto-scaling the cluster Understand possible approaches to traffic routing in Kubernetes Who this book is forThis book is for software developers and DevOps engineers looking to understand how to work with Kubernetes for orchestrating containerized applications and services in the cloud. Prior experience with designing software running in operating system containers, as well as a general background in DevOps best practices, will be helpful. Basic knowledge of Kubernetes, Docker, and leading cloud service providers assist with grasping the concepts covered easily.

Gain practical knowledge of shellcode and leverage it to develop shellcode for Windows and Linux operating systems, while understanding the countermeasures in place and how these can be bypassed Key Features Get up and running with shellcode fundamentals Develop Shellcode for Windows and Linux Understand the building blocks of shellcode Book DescriptionShellcoding is a technique that is executed by many red teams and used in penetration testing and real-world attacks. Books on shellcode can be complex, and writing shellcode is perceived as a kind of "dark art." Offensive Shellcode from Scratch will help you to build a strong foundation of shellcode knowledge and enable you to use it with Linux and Windows. This book helps you to explore simple to more complex examples of shellcode that are used by real advanced persistent threat (APT) groups. You'll get to grips with the components of shellcode and understand which tools are used when building shellcode, along with the automated tools that exist to create shellcode payloads. As you advance through the chapters, you'll become well versed in assembly language and its various components, such as registers, flags, and data types. This shellcode book also teaches you about the compilers and decoders that are used when creating shellcode. Finally, the book takes you through various attacks that entail the use of shellcode in both Windows and Linux environments. By the end of this shellcode book, you'll have gained the knowledge needed to understand the workings of shellcode and build your own exploits by using the concepts explored. What you will learn Gain a thorough understanding of shellcode Get to grips with assembly language and its key purpose in shellcode development Identify key elements of memory registers Explore debuggers and their use cases Get up and running with hands-on shellcode creation for both Windows and Linux Exploit Windows and Linux operating systems using shellcode Assess countermeasures of Windows and Linux Who this book is forThis book is for red teamers, penetration testers, and anyone looking to learn about shellcode and find out how it is used to break into systems by making use of simple to complex instructions of code in memory. Basic shellcode knowledge is helpful but not mandatory to understand the topics covered in this book.