The OS provides a variety of facilities and services in the form of utility programs, such as editors and debuggers, for program development, which is also referred to as application program development tools.

The OS handles different processes, such as loading data into the memory and scheduling, which must be performed to execute programs.

: The OS provides a uniform interface that hides complex sets of instructions for I/O devices' operation

The OS encompasses a detailed understanding of the structure of data contained in a file storage and can provide some protection mechanisms to control file access.

The OS controls access to the whole system and to some specific system resources through access functions and authorizations.

The OS can detect errors, such as device failure and software errors, and provide appropriate responses that would clear the error condition with the least impact on running applications

The OS must be able to collect usage statistics from various processes, such as response time, that can be used as a basis for system performance improvements.

The ISA defines the collection of machine language instructions that a computer can follow. The OS has access to additional machine language instructions that deal with managing a system's ISA.

defines a standard for binary portability across programs. It defines the system call interface to the OS and the hardware resources and services available in a system through the ISA.

allows a program to the hardware resources and services available in a system through that ISA, supplemented with high-level language library calls. It also enables easier porting of application software.

From late 1940s to the mid-1950s, programmers interact directly with computer hardware since operating systems (OS) are not yet available. Computers are run from a console consisting of display lights, toggle switches, an input device, and a printer

Serial processing presented two (2) main problems which are: Installations used a hardcopy sign-up sheet to reserve computer time. A user could sign up for an allocated block of time, but is unable to maximize the allocation. Thus, resulting in wasted computer processing time

Serial processing presented two (2) main problems which are: A single program, called a job, involves numerous sequenced set-up processes that involve mounting and dismounting of tapes and setting up card decks.

To improve processor utilization, the concept of batch operating system was developed in the mid-1950s by General Motors Research Laboratories. It processed jobs in bulk, with predetermined input from files or other data resources.

This kind of operating system is more sophisticated compared to single programmed systems. Several ready-to-run jobs must be kept in the main memory, requiring some form of memory management. If several jobs are ready to run, the processor decides which one to run, and that decision requires a specific algorithm for scheduling. It basically allows the processor to handle multiple jobs at a time.

multiple users simultaneously access the system through terminals, with the operating system interleaving the execution of each user program in a short burst time or quantum computation.

was one of the first timesharing operating systems that was developed. It was developed at the Massachusetts Institute of Technology (MIT) by the group Project MAC, for the IBM 709 computer system.

Kernel Components of Microsoft Windows OS:

Windows Executive – This contains the core OS modules/services for specific functions and provides an API for user-mode software. The following are its functions:

Windows Executive – This contains the core OS modules/services for specific functions and provides an API for user-mode software. The following are its functions:

- This provides a framework through which I/O devices are accessible to applications.

Windows Executive – This contains the core OS modules/services for specific functions and provides an API for user-mode software. The following are its functions:

This improves the performance of file-based I/O by allowing recently referenced file data to reside in the main memory for quick access.

This creates, manages, and deletes Windows Executive objects that are used to represent resources such as processes, threads, and synchronization objects, while enforcing uniform rules for retaining, naming, and setting the security of the objects.

This determines which drivers are required to support a particular device and loads those drivers.

This coordinates the power consumption among various devices. It can be configured to reduce power by shutting down idle devices or the entire system, or setting the processor to sleep

This enforces the access validation and audit-generation rules for all protected objects including files, processes, address spaces, and I/O devices.

This manages virtual addresses, physical memory, and paging files on a disk.

This creates, manages, and deletes processes and thread objects.

This is responsible for implementing and managing the system registry, which serves as the repository for both system-wide and per-user settings of various parameters.

This implements an efficient cross-process call mechanism for communication between local processes implementing services and subsystems

This is considered the core software of the OS. It controls the execution of the processors. This manages thread scheduling, process switching, exception and interrupt handling, and multiprocessor synchronization. Note that the Kernel's own code does not run in threads.

– This isolates the OS from platform-specific hardware variances. It makes each computer's system bus, direct memory access (DMA) controller, interrupt controller, system timers, and memory controller look the same to the Windows Executive and Kernel components.

These are dynamic libraries that extend the functionality of the Windows Executive.

This implements the graphical user interface (GUI), such as the user interface controls and illustrations.

User-mode Processes:

These include user-mode services such as the session manager, the authentication subsystem, the service manager, and the log-on process

User-mode Processes:

These involve services used by both Microsoft and other external software developers to extend system functionality and run background user-mode activity on a Windows system

User-mode Processes:

These provide different operating system environments and support Portable Operating System Interface (POSIX) and Win32 subsystems

User-mode Processes:

These include executable (EXE) programs and dynamic link libraries (DLLs) that provide the functionality a user needs to make use of a system.

assic UNIX System • The classic UNIX system was developed at Bell Labs which was partly written in assembly language and was later converted into C language. It was initially called Uniplexed Information and Computing Service (UNICS).

The architecture of a classic UNIX has three (3) levels:

User level - focuses on the linked programs and libraries

Hardware level - focuses on the physical hardware and interface

System kernel - focuses on the overall operation of the system.

This supports system calls from applications, other interface software, and the components of the C compiler, such as the compiler itself, the assembler, and the loader.

A joint development by AT&T and Sun Microsystems. The system kernel of this operating system has a clean implementation. The new feature in this OS release includes real-time processing support, process scheduling classes, dynamically allocated data structures, virtual memory management, virtual file systems, and a preemptive system kernel

The Linux operating system is composed of independent blocks called

two (2) vital characteristics of the Linux loadable modules:

The modules can be loaded and linked into the kernel while the kernel is already in memory and executing. A module can also be unlinked and removed from the memory at any time.

two (2) vital characteristics of the Linux loadable modules:

The modules are arranged in hierarchical order. Modules serve as libraries when they are referenced by other modules higher up in the hierarchy, and as clients when they reference modules further down.

It is a unique identifier for each process

It indicates the current activity of a process

It refers to the priority level relative to other processes

It indicates the address of the next instruction to be executed for a particular process.

It contains pointers to program codes and data associated with the process, including any memory blocks shared with other processes

These are the data present in a processor's registers during process execution.

This includes different information associated with the input/output status of a process, such as the outstanding I/O requests and I/O devices assigned to the process.

This includes different tracking information associated with the process, such as the amount of processor time, the clock time used, and time limits.

The elements of a process are stored in a data structure called _______The core concept of the process control block is that it contains sufficient information so it is possible to interrupt a running process and later resume the operation as if no interruption occurred.

Two-State Process Model:

When the OS creates a new process, it creates a process control block for the new process and adds the new process into the not running state of the system. Then, the process waits for an opportunity to execute.

Two-State Process Model:

The dispatch portion of the OS selects a particular process to run. Then, it enters the running state. Intermittently, the currently running process will be interrupted and the dispatch portion has to select other processes to run.

These are used to keep track of both the main and the secondary memory. A part of the main memory is reserved for OS utilization,

–These are used by the OS to manage the input and output devices and channels of a computer system at any given point in time.

These tables hold information regarding the existence of files and its corresponding attributes through a file management system.

These tables are maintained by the OS to manage processes.

Process control blocks are also referred to as _______The location of a process image will depend on the memory management scheme being used.

Process Attributes: A multiprogramming system requires a great deal of information about each process that resides in a process control block.

This involves unique numeric identifiers that are assigned to specific processes, which can simply be an index into a primary process table, or identifiers for cross-referencing process tables.

This consists of processor registers' information. During process execution, information are in the registers. When a process is interrupted, all information in the registers must be saved so it can be restored when the process resumes execution.

This contains the additional information needed by the OS to control and coordinate various active processes, such as the data structure, resource ownership and utilization information, and process privileges.

When a new process is to be added to those currently being managed, the operating system builds the data structure that will manage the process and allocates address space in the main memory for the process.

: When the operating system controls the currently running processes, a process switch may occur at any time. Thus, the OS needs to provide a regaining control feature if a process is blocked, suspended, or paused.

Interrupts are external events that are independent of the currently running process,

traps are related to errors or exception conditions generated within the currently running process.

supervisor call due to an explicit request can still occur to interrupt a process execution.

Any computer system must provide means for a process to indicate its completion. A batch job may include a halt instruction or an explicit OS service call for termination.