What Are Status Registers In Os

The three major jobs of a figurer are Input, Output, and Processing. In a lot of cases, the well-nigh important chore is Input / Output, and the processing is but incidental. For example, when you browse a web page or edit any file, our immediate attention is to read or enter some information, not for computing an answer. The principal function of the operating system in computer Input / Output is to manage and organize I/O operations and all I/O devices. In this chapter, you will learn about the diverse uses of input output devices concerning the operating system.

Overview of Input / Output organization

The controlling of diverse devices that are continued to the computer is a central concern of operating-system designers. This is because I/O devices vary and then widely in their functionality and speed (for example a mouse, a hard deejay and a CD-ROM), varied methods are required for controlling them. These methods grade the I/O sub-system of the kernel of Os that separates the residual of the kernel from the complications of managing I/O devices.

I/O Hardware

Computers operate many huge kinds of devices. The full general categories of storage devices are like disks, tapes, transmission devices (similar network interface cards, modems) and human being interface devices (like screen, keyboard, etc.).

A device communicates with the operating organisation of a figurer past transferring signals over cable or even through the air. The peripheral devices communicate with the machine through a connection point also called ports— (one example is a serial port). When devices use a set of wires or cables, that connecting cables are called a "bus." A autobus is a collection of wires and a firmly divers protocol which specifies a set of messages that tin can be sent on the wires.

Operating Arrangement Using I/O Port

An I/O port usually consists of four different registers. These are (1) status, (2) control, (iii) information-in, and (4) data-out registers.

The data-in register is read by the host for getting input.
The data-out annals is written by the host for sending output.
The status annals holds bits which can be read by the host.
The control register is written by the host for starting a control or for irresolute the way of any device.
The data registers are normally 1 to iv bytes in size. Some of the controllers have FIFO chips which concord several bytes of input or output data for expanding the capacity of the controller across the size of the data annals.

Polling

The complete protocol used to interact with the host and a controller tin can be difficult for the OS, just the necessary handshaking notion is simple. You tin can express handshaking with an instance. You assume that two bits have been used for coordinating the producer - consumer human relationship among the controller and the host. The controller points to its state using the decorated bit in the status register.

The host marks output through a port, with the controller using handshaking similar:

The host ofttimes reads the busy bit till that flake gets clear.
The host so sets the write, bit in the command register and so writes a byte to the data-out annals.
The host and then puts the command-set up bit.
As the controller notices that the command - set bit has been set, it sets the decorated scrap.
The controller then reads the command register. It reads the data-out register for getting the byte and performs the I/O to the device.
The controller clears the command - set flake then clears the mistake bit inside the condition register for indicating that the device I/O succeeded.