Betriebsysteme

Operating Systems

• Users interact with application programs.
• Application programs provide feedback to users.
• Application programs use operating system functions to communicate with hardware.
• The operating system receives requests from application programs.
• It validates these requests and forwards them to the hardware.
• Application programs receive feedback from the operating system about accepted and completed requests.
• Hardware executes commands from the operating system.
• The operating system receives feedback from the hardware and informs about hardware errors when possible.

Interaction Between User, Software, OS, and Hardware

• User interacts with software applications.
• Software communicates with the OS, sending requests and providing user feedback.
• The OS receives and checks requests from software for legitimacy.
• Application programs receive feedback about approved or rejected requests.
• Hardware executes commands.
• The OS receives acknowledgements about executed commands

Tasks of Operating Systems

• The core task is the management of operating resources.
• This is also known as resource management.
• Includes process management, memory management, device management, file management, and energy management.

Computer Architecture

• An area of computer science focusing on the internal and external structure of computer systems.

Central Processing Unit (CPU)

• The control unit fetches and executes machine instructions.
• The control unit is the instruction processor.
• The arithmetic logic unit (ALU) is the data processor, performing logical and arithmetic operations.
• Machine instructions and data are stored in a common memory.
• Input/output manages external device connections.
• Components are interconnected by a transport system known as a bus system.
• Control unit and ALU are often combined into a CPU.
• Registers are small, fast storage areas.

Register Definition

• A digital storage area located directly on the CPU.
• It stores a small group of binary values (bits).

Control Unit (Instruction Processor)

• The control unit sends the address of the current instruction to memory.
• Receives the instruction from that address.
• It executes the command.
• The address of the current instruction is managed using a register called the Program Counter (PC).
• The received command from memory is managed using a register called the Instruction Register (IR).

Bus

• Used for parallel data transfer.

Address Bus

• A bus in which a parallel transferred group of bits is an address.

Data Bus

• A bus where the parallel transferred group of bits are data

ALU (Data Processor)

• The calculation Unit is part of the CPU
• It executes calculations from the control unit.
• The main part of the Calculation Unit is the ALU (arithmetic-logical Unit).
• A connection between the control unit and the Calculation Unit is bidirectional. -The Steuerwerk orders a function via control lines -The Calculation unitt returns the status of the bill (flags) to the control unit.

Functions Provided

• Addition (A + B)
• Subtraction (A - B)
• Multiplication (A * B)
• Conjunction (logical AND, bitwise)
• Disjunction (logical OR, bitwise)
• Comparison of A and B (bitwise)

Flags

• Status bits sent from the Calculation Unit to the control unit after each operation.
• Examples include:
  • Last result equal to zero (ACC = 0?)
  • Both operands equal (A = B?)
  • A less than B (A < B?)
  • Overflow?

Memory Unit

• CPU-Memory Unit interactions are simplified via special CPU registers assigned exclusively to memory unit communication.
• Memory Address Register (MAR): The control unit stores addresses to be accessed in memory.
• Memory Data Register (MDR): Data for read/write operations are stored here before processing or transfer.
• During a read, data from memory is placed in the MDR.
• During a write, data to be written must be in the MDR before transfer to memory.

Control Bus

• A bus where the parallel transferred group of bits are Steuerinformation.
• The coming from controller

Program Types

• Application Program: Solves problems for computer users (e.g., word processors, email clients, browsers).
• System Program: Manages computer operations.
• Operating systems are special system programs.
• Operating System: Provides elementary services to users and applications.
• It controls program execution and manages the computer system.

Operating Resources

• Betriebsmittel (Resource): Any hardware or software asset of a computer.

Hardware Resource

• A hardware component of the computer.

Software Resource

• A process or file on a storage medium.

Classifications

• Entziehbares Betriebsmittel (Preemptible Resource): A resource that can be taken away from a process without negative consequences.
• A CPU is a preemptible resource.
• Nicht entziehbares Betriebsmittel(Non-Preemptible Resource): A non-preemptible resource must be available to a process for as long as it needs it.
• Premature removal causes undesirable consequences (e.g., a printer).
• Exklusiv nutzbares Betriebsmittel (Exclusively Usable Resource): Only one process can use it at a time.
• It can be exclusively usable and preemptible, or exclusively usable and non-preemptible.
• A CPU with one core is exclusively usable and preemptible.
• A printer is exclusively usable and non-preemptible.
• Gemeinsam nutzbares Betriebsmittel (Shared Usable Resource): Multiple processes can use quasi-simultaneously usable resources.
• A hard drive is an example.
• Several processes can have files open at the same time on the hard drive.
• Only concurrent access of the involved processes to several files is technically impossible.

Types of Operating Systems

Operating Systems for Mainframes

• Handle many requests quickly and are optimized for input/output and large storage.
• Transaction-oriented, processing many transactions rapidly.
• An is z/OS by IBM.

Operating Systems for Servers

• Primarily addressed over a network by clients.
• Clients expect fast response times.
• Common examples include Windows Server 2008/2012, Unix, and Linux.
• Serve as file, print, email, and terminal servers.

Operating Systems for Laptops and PCs

• Used daily by most people.
• A single user runs multiple programs quasi-simultaneously.
• Typically dialog-oriented, where the user provides input and the operating system responds quickly.
• Today, GUIs are commonly used (e.g., Windows 10/11, MacOS X, Linux with KDE or Gnome).

Batch Jobs

• Early programs processed as batch jobs, completing each job before starting the next.
• Processes were executed in sequence, with the last process waiting the longest.

Multitasking

• Multiple processes alternate in CPU usage.
• This marks a milestone in computing, offering better resource utilization and new interaction possibilities.

Kernel Mode, User Mode, and System Calls

• To secure when multiple processes run, processes must have restricted data access and fair CPU time.
• This requires a central authority.

Kernel Mode

• Any command can be executed, with access to all memory and resources.
• It has the highest privileges, indicated by a control register.
• The operating system typically works in Kernel Mode.

User Mode

• Only a limited set of commands can be executed.
• Can not be used to access all memory or resources.
• Application programs work in User Mode, which is restrictive.

Transitioning Between Modes

• Transitioning from Kernel Mode to User Mode is straightforward.
• Rights are restricted, with no security concerns: the operating system allocates the CPU to an application program.
• Transitioning from User Mode to Kernel Mode requires system calls, because application programs are not meant to have extensive Kernel Mode rights.

System Call

• Requests an operating system function executable only in Kernel Mode.
• The User Mode process relinquishes control to the operating system, which performs the function after security checks.
• Control returns to User Mode.
• An application program wants to access a file, the operating system provides system calls for file access (e.g., open, read, write, close).
• A system call triggers a software interrupt.
  • The process is halted, and the interrupt service routine is executed (operating system code):
    • Switches to Kernel Mode, performs necessary checks, performs or denies the file access, switches back to User Mode, restarts the interrupted process, and provides a return value.