unit 1

• Bit


  The smallest possible unit of information
• Digital systems store and process information in binary form, i.e., in the form of sequences of 0 and 1
• One bit


  Corresponds to the amount of information in an answer to a question with only two possibilities
• Binary coding designates 0 or 1 to each of the two possible answers
• If there are more than two possible answers, bit sequences are required to store the information
• Real world applications of binary


  • Light switch (on/off)
  • Flashlight (on/off)
  • Optical storage media (peaks/valleys)
  • Magnetic storage media (magnetic states)
• All data stored in a computer system, as well as all programs that are executed on a computer system, manifest themselves as sequences of 0 and 1
• Boolean operations


  Algebraic structure with the two elements, 0 and 1, and the logical operations AND, NOT, and OR
• AND operation


  • Evaluates to 1 if both inputs are 1, otherwise 0
• OR operation


  • Evaluates to 1 if at least one of the inputs is 1
• NOT operation


  • Negates the input value (1 becomes 0, 0 becomes 1)
• All processing units are constructed on the basis of these simple Boolean operations
• Storing numbers and letters


  Defined mappings and standards like ASCII or UTF-8 are used to represent them as bit sequences
• UTF-8 encoding


  • 01010011 for the letter "S"
• To perform mathematical calculations, numbers are first converted from decimal to binary, then calculated in binary, and finally converted back to decimal
• Von Neumann architecture


  General architectural concept for the construction of universal computers, introduced in 1945
• Units of the Von Neumann architecture

  • Memory
  • Control unit
  • Arithmetic logical unit (ALU)
  • Input/output (I/O) units
  • Bus system
• Memory


  • Used to store binary coded data and programs, divided into small areas with unique addresses
• Control unit


  • Responsible for loading program commands from memory, interpreting them, and coordinating the ALU
• Arithmetic logical unit (ALU)


  • Performs arithmetic and logical operations on data
• Input/output (I/O) units


  • Interface between the system and its surrounding environment, responsible for data and program flow
• Bus system


  • Data transmission system used by all units for communication, determines the speed of the computer
• The von Neumann architecture allows for universal computing, as the internal structure does not determine how data is processed
• How the von Neumann computer works

  1. Control unit loads first command into ALU

  2. Command is executed

  3. Next command is loaded and executed

  4. Sequence repeats until program ends
• Distributed software system


  Software system that can only be used in conjunction with several computers connected via a communication network
• Typical elements in distributed systems

  • Server
  • Client
  • Communication network
  • Agreement on message structure
• Server


  • Computers that make functions accessible to other computers via a communication network
• Client


  • Computers using services offered by servers
• Communication network


  • Connects clients and servers, consists of physical components, technical routing/transfer components, and network interfaces
• Network interface


  Enables a computer to communicate with a communication network
• Server


  A service provider, by installing and starting the appropriate software systems
• Most systems within an enterprise network act as both a server and a client, depending on the service considered
• Communication network


  Connects clients and servers, consisting of physical components for data transmission, technical components for routing and transferring data, and network interfaces to connect a device
• Network interface


  Enables a computer to communicate with other computers, including the physical connection and software support from the operating system
• Message


  Logically related information sent by an application, which is transformed into a bit sequence and split into smaller data packets for transmission
• Conceptual models for communication

  • Internet protocol suite (TCP/IP) model and open systems interconnection (OSI) reference model describe network architectures that encode and decode messages in layers
  • OSI model is more detailed with 7 layers, while TCP/IP has 4 layers
• Protocol


  A set of conventions that govern the interaction of processes, devices, and other components within a system
• Application layer


  • Contains application-specific definitions for the structure and exchange of messages, e.g. HTTP and SMTP
• Presentation and session layer

  • Defines syntax and semantics of information, responsible for character encoding, data compression, encryption/decryption, and enabling sessions between remote computers
• Transport layer


  • Divides messages into smaller units, ensures all data packets arrive at the recipient, and lines up packets in the correct order