I / O System

Basically, the computer's main task is the processing and I / O. In fact, most of the time used to process I / O while the processing is only incidental. So, in the context of I / O, the role of the operating system is to regulate and control the device I / O and I / O.  I / O devices vary widely. Therefore, how to control these devices received a major in computer organization. Imagine, I / O devices are very many in number and each device has a function and its own pace, of course, require different methods.
Therefore, the known classification of the device I / O to block devices and character devices, although there are devices that do not belong to any of these two categories. The device is connected to a computer through a port, set by the device controller and communicates with the processor and other devices through the bus.

The device communicates with the processor via two approaches and instruction memory mapped I / O directly. When a processor wants to access a device, he will continue to check the device to determine its status, if allowed to be accessed. How this is done repeatedly called to the polls.

Meanwhile, when a device wants to tell the processor when readily accessible, the device uses an interrupt. Both methods has advantages and disadvantages of each. The existence of Direct Memory Access (DMA) can reduce the CPU load due to the transfer of data between devices and memory without going through the CPU. Differences details for each tool will be encapsulated in a kernel module called a device driver. As for knowing when and how long a process to use clock and timer.

Categories of  I / O

At this present time, there are various kinds of  I / O devices such as storage devices (disk, tape), transmission devices (network cards, modems), and devices with a user interface (screen, keyboard, mouse). In general, I / O devices can be divided into two categories namely:



1. Block device.
A device that stores information in a certain-sized blocks (typically 512 to 32768 bytes) and each block has a respective address. Each block on this device can be accessed and written independently. Examples of block device is a disk.

2. Character device.
A device that sends and receives a row of characters regardless of the block structure. Examples of character devices are printers, network interfaces and devices rather than disk. However, this division is not entirely true because there are devices that do not meet both these criteria the clock. Clock is a device that does not have the address block, do not send and receive interrupt the sequence of characters but only within a certain timeframe.

Component I / O
Unit I / O consists of two components, namely:
1. Mechanical Components. Mechanical components are I / O devices such as the mouse itself,
monitors, etc..
2. Electronic Components. Electronic component is also called the controller device.
The device is not connected directly with the processor, the controller was associated with the processor.

Note : I  = input, O = output, /  = or.