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.

How To Connect To The Computer

I / O devices communicate with the computer system through signals transmitted through wires or air (wireless). I / O devices connected to the engine through a point called a port. Port I / O consists of four registers, namely:
1. Data-in register. This register will read the CPU to get input.
2. Data-out registers. CPU write a bit here as output data.
3. Status. CPU will read this register to know the status of the device. Device status
could indicate whether the available inputs in the data-in registers, the device completed the
duties properly or an error in the device.
4. Control. These registers are written by the CPU to initiate a command or to change the mode
device. One example is the replacement of the device mode bits contained in control registers
in serial port that serves to select the transfer rate supported by the serial port
them. The bus is a collection of wires and protocols that define a set of messages that can be sent over the wire. Some devices can be connected to the same bus. When the device A to device B is connected, the device B is connected to the device C and so on until the last device connected to the computer, the circuit device is called a daisy chain. Daisy chain also serves as a bus.

The structure of the bus on the PC

PCI (Peripheral Component Interconnect) bus is a high-speed bus that connects the processor to the memory subsystem, high-speed devices and the Expansion bus associated with a slower device such as keyboard, serial ports and port paralell. SCSI or Small Computer System Interface (read: skazi) is the bus that connects multiple disks to the SCSI controller. With SCSI, you can get up to seven devices connected to the computer but it will slow down your computer at start-up.

We all are familiar with storage devices like floppy drives, hard drives and CDROM drives. Typically these devices are connected to the computer via the IDE (Integrated Drive Electronics). The interface brings together the controller to the drive, so with simpler instructions and routes that are closer between the drive and controller, making it faster and easier to use. Buses, ports and devices can be operated by a controller which is a collection of electronic devices. Serial-port controller is one of the controller device that is simple because only a chip that controls the signal from the cable in the port. On the other hand, there is also a complex device controller SCSI controller that is so complex as to be implemented specifically as a separate circuit board inside the computer. This is called a host adapter. SCSI controller contains a processor, microcode, and some of its own memory.