It exploits the hardware resources of one or more processors to provide a set of services to system users. The ______ also manages secondary memory and I/O

Controls the operation of the computer and performs its data processing functions. When there is only one processor, it is often referred to as the central processing unit (CPU).(input/output) devices on behalf of its users.

Stores data and programs. This memory is typically volatile; that is, when the computer is shut down, the contents of the memory are lost.

Move data between the computer and its external environment. The external environment consists of a variety of devices, including secondary memory devices (e. g., disks), communications equipment, and terminals.

Provides for communication among processors, main memory, and I/O modules.

Enable the machine or assembly language programmer to minimize main memory references by optimizing register use.

Used by the processor to control the operation of the processor and by privileged OS routines to control the execution of programs.

______can be assigned to a variety of functions by the programmer. In some cases,they are general purpose in nature and can be used with any machine instruction that performs operations on data.

It contain main memory addresses of data and instructions, or they contain a portion of the address that is used in the calculation of the complete or effective address

it is a common mode of addressing that involves adding an index to a base value to get the effective address.

With segmented addressing,memory is divided into segments, which are variable-length blocks of words.

If there is user-visible stack2 addressing, then there is a dedicated register that points to the top of the stack.This allows the use of instructions that contain no address field, such as push and pop.

Contains the address of the next instruction to be fetched

Contains the instruction most recently fetched

(also referred to as flags) are bits typically set by the processor hardware as the result of operations.

Data may be transferred from processor to memory or from memory to processor.

Data may be transferred to or from a peripheral device by transferring between the processor and an I/O module.

The processor may perform some arithmetic or logic operation on data.

An instruction may specify that the sequence of execution be altered.

is a program that controls the execution of application programs and acts as an interface between applications and the computer hardware.

An OS makes a computer more convenient to use.

An OS allows the computer system resources to be used in an efficient manner.

An OS should be constructed in such a way as to permit the effective development, testing, and introduction of new system functions without interfering with service.

The OS provides a variety of facilities and services, such as editors and debuggers, to assist the programmer in creating programs.

A number of steps need to be performed to execute a program. Instructions and data must be loaded into main memory, I/O devices and files must be initialized, and other resources must be prepared.

Each I/O device requires its own peculiar set of instructions or control signals for operation. The OS provides a uniform interface that hides these details so that programmers can access such devices using simple reads and writes.

For file access, the OS must reflect a detailed understanding of not only the nature of the I/O device (disk drive, tape drive) but also the structure of the data contained in the files on the storage medium.

For shared or public systems, the OS controls access to the system as a whole and to specific system resources. The access function must provide protection of resources and data from unauthorized users and must resolve conflicts for resource contention.

A variety of errors can occur while a computer system is running. These include internal and external hardware errors, such as a memory error, or a device failure or malfunction; and various software errors, such as division by zero, attempt to access forbidden memory location.

Most installations used a hardcopy sign-up sheet to reserve computer time.Typically, a user could sign up for a block of time in multiples of a half hour or so.

A single program, called a job, could involve loading the compiler plus the high-level language program (source program) into memory, saving the compiled program (object program) and then loading and linking together the object program and common functions

The central idea behind the simple batch-processing scheme is the use of a piece of software known as the _____

The monitor controls the sequence of events.

For this to be so, much of the monitor must always be in main memory and available for execution. that portion is referred to as the______

At a certain point, the processor is executing instructions from the portion of main memory containing the monitor. These instructions cause the next job to be read into another portion of main memory.

This is a special type of programming language used to provide instructions to the monitor

While the user program is executing, it must not alter the memory area containing the monitor. If such an attempt is made, the processor hardware should detect an error and transfer control to the monitor. The monitor would then abort the job, print out an error message, and load in the next job.

A ____ is used to prevent a single job from monopolizing the system. The ____ is set at the beginning of each job. If the ___ expires, the user program is stopped, and control returns to the monitor.

Certain machine level instructions are designated privileged and can be executed only by the monitor. If the processor encounters such an instruction while executing a user program, an error occurs causing control to be transferred to the monitor.

Early computer models did not have this capability. This feature gives the OS more flexibility in relinquishing control to and regaining control from user programs.

A user program executes in a ______, in which certain areas of memory are protected from the user’s use and in which certain instructions may not be executed.

The monitor executes in a system mode, or what has come to be called ______, in which privileged instructions may be executed and in which protected areas of memory may be accessed.

________ allows the processor to handle multiple batch jobs at a time, ________ can also be used to handle multiple interactive jobs.

Just as multiprogramming allows the processor to handle multiple batch jobs at a time, multiprogramming can also be used to handle multiple interactive jobs. In this latter case, the technique is referred to as ______, because processor time is shared among multiple users.

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

It is primitive compared to present-day time sharing, but it worked. It was extremely simple, which minimized the size of the monitor.