هندسة الحاسوب: وحدات البيانات والمعالجة

Introduction to Operating Systems

• Operating systems act as intermediaries between users and computer hardware.
• Goals of operating systems include making user programs easier to execute and solving user problems more easily.
• Operating systems also make computer systems more user-friendly and utilize computer hardware efficiently.

Computer System Structure

• Computer systems consist of four components: hardware, operating system, application programs, and users.
• Hardware provides basic computing resources (CPU, memory, I/O devices).
• Operating systems control and coordinate the use of hardware among various applications and users .
• Application programs define how system resources are used to solve computing problems for users.
• Users (people, machines, other computers) interact with the system.

Operating System Definition

• Operating systems are resource allocators. They manage all system resources and decide how resources are used efficiently and fairly.

• Operating systems control the execution of programs. They prevent errors and inappropriate use of the computer system..

• There's no single, universally accepted definition of an operating system. The concept of the "kernel" is commonly cited as the one program running continuously on a computer.

• Everything else is either a system program (bundled with the OS) or an application program.

Computer Startup

• At power-up or reboot, a bootstrap program is loaded.
• This program, typically stored in ROM or EPROM (firmware), initializes all system aspects.
• Then, it loads the operating system kernel and starts its execution.

Computer System Operation

• I/O devices and CPUs can work concurrently.
• Each device controller is responsible for a type of device.
• Each controller has a local buffer memory.
• CPUs transfer data to and from main memory and the local buffers of controllers.
• I/O is transmitted from a device to the controller's local buffer.
• Device controllers inform the CPU when their operations are complete by causing an interrupt.

Common Functions of Interrupts

• Interrupts transfer control to an interrupt-service routine, generally via the interrupt vector.
• Interrupt vectors contain addresses of service routines.
• Interrupt architecture saves the address of the interrupted instruction.
• Trapping or exceptions are software-generated interrupts due to errors or user requests.
• Operating systems are interrupt-driven.

Interrupt Handling

• Operating systems preserve CPU state (registers and program counter) during interrupts.
• The OS determines the interrupt type (polling, vectored).
• Separate code segments handle actions for different interrupt types.

Storage Definitions and Notation Review

• The fundamental unit of computer storage is the bit, which can store 0 or 1.
• A byte consists of 8 bits. Bytes are the most common and convenient storage unit in most computers.
• Words are more complex units of data that is native to a specific type of computer architecture.
• Computer storage is generally measured and manipulated in bytes – kilobytes (KB, 1024 bytes), megabytes (MB, 1024² bytes), gigabytes (GB, 1024³ bytes), terabytes (TB), and petabytes (PB).
• Manufacturer's often use rounded values when discussing megabytes and gigabytes but these are just approximations and not the equivalent measurements used in networking.

Storage Structure

• Main memory is the only storage media directly accessible to the CPU.
• Main memory is volatile.
• Secondary storage expands main memory's capacity and is nonvolatile.
• Hard disks are commonly used secondary storage devices.
• Hard disks are rigid platters coated with magnetic recording material.
• The disk surface is logically divided into concentric tracks subdivided into sectors.
• Solid-state disks (SSDs) are faster than hard disks and are nonvolatile.

Storage Hierarchy

• Storage systems are organized hierarchically based on speed, cost, and volatility.
• Caching involves temporarily copying information from slower storage to faster storage for quick access.
• Device drivers act as interface between device controllers and the kernel.

Direct Memory Access Structure

• Direct Memory Access (DMA) is used for high-speed I/O devices.
• DMA controllers transfer data blocks from buffers directly to main memory without CPU involvement.

How a Modern Computer Work

• A device driver prepares I/O operations by loading registers in the device controller.
• Device controllers check the registers for instructions.
• Data is transferred from the device to the controller's buffer.
• After completion, the device controller informs the device driver via an interrupt.
• The driver returns control to the operating system.
• DMA is used when bulk data movement is necessary to improve performance.

Computer System Architecture

• Most systems use a single general-purpose processor.
• Some systems include special-purpose processors.
• Multiprocessors (parallel systems) are increasing in use and offer several advantages, including increased throughput, economy of scale, and improved reliability.
• Two main types of multiprocessors include asymmetric multiprocessing and symmetric multiprocessing.

Clustered Systems

• Clustered systems are composed of multiple systems working in conjunction.
• Clustered systems often use a storage area network (SAN) for shared storage.
• Cluster types include asymmetric and symmetric clustered systems.
• Applications for clustered systems might include those requiring high availability, high-performance computing, or distributed lock management.

Operating System Structure

• Multiprogramming (batch systems) are used for efficiency when dealing with high numbers of jobs or processes.
• A subset of jobs are stored in memory for CPU to execute them.
• Multiprogramming scheduling algorithms are employed to select and execute a job.
• Timesharing (multitasking) maximizes user interactions with a job.
• Processes in memory are swapped in and out in timesharing.
• Virtual memory enables execution of processes larger than available RAM .