Parallel Port :- It is an input port that manages 8 bit of data at a time. The transmission in this case is one byte at a time on different data signal wires. It is the oldest port used in computers. All the bits that make up the character are transmitted through this port, centronics port or printer port. It is one of the most versatile and reliable printer connection techniques in the computer industry. This port is simple straight forward has a good performance. It consists of three separate registers called data register, status register and control register. The heart of parallel port is data register. Control register is also bidirectional and in manager the behaviour of the port and sets the conditions under which new characters are requested from the CPU. The control register and status register handle the handshaking lines of the port.
The older BIOS version supported only two ports but the current BIOS version surproted upto four parallel port in a computer system.
The parallel port uses 25 pin female DB connector. A parallel cable is used with it which is purchased with the printer itself.
USB Port :- USB stands for Universal serial bus. It is a new type of interface for low to medium speed peripherals. USB port have almost replaced the old serial and parallel port on computer because of its exceptional capability of Hot Swapping. Got Swapping allows the device to be attached physically, without shutting down or rebooting of the system. Most of the modem computers include the USB port and it is used to connect a variety of different devices to computer ranging from keyboard, mouse to camera, printer or telephone. The speed of USB is very high and is 12 MBps with the translation rate of 1.5 MB/sec. USB can also provide an interface for DSL and cable modems. Typically a USB port can support 127 devices and at present almost every type of PC peripheral is available in a USB version.
USB is serial interface and transmits one bit of data at a time, however it transmits data much faster than the strandard serial port. It has four conductors providing a single bus running at 12 MBps. All the devices plugged into USB share the same bandwidth. In addition to the data channel, the USB cable can supply power to certain type of devices like keyborad and mouse, which need low power. A USB device can perform two roles called Hub and Function.
The USB uses a tiered star topology which means that some of the USB devices called USB Hub can serve as connection port for other devices are plugged into the Hub.
The USB host controller manager and controlles the drives software and data flow required by the devices connected to the bus. It also allocates the electrical power to the USB devices. There are two types of USB host controller called :-
> Universal Host Controller Interface
> Open Host Controller Interface
COM Port :- COM port is another name for serial ports as used by DOS. In DOS the device name used to denote a serial communication port is the COM port. Older BIOS version supported only two COM ports called COM1 and COM2. But never BIOS releases support four COM port i.e. COM1, COM2, COM3, COM4. At the same time Micro channel bus system can support unto 8 O2F8h in all systems. However, for other COM port i.e. COM 3to COM8 the address depends on the system bus architecture. The specific I/o addresses for each COM port are kept in the BIOS data area of RAM starting at 0400h. Whenever a new COM port is installed in a system, it must be assigned to a valid base address and interrupt. Only one COM port can be assigned to a base address. If more than one COM port is assigned to the same base address, certainly system problems will occur.
Special Port :- Besides these three standard port there are so many other ports which are used for connecting a specific device. They all are dedicated ports and because of this they all are counted in the special ports. Some of the dedicated special ports are keyboard port, mouse port, game or joystick port, modem port, audio port, video port etc. All of them are specified for their specific devices and are dedicated to them.
LST Port :- In DOS, the device name use to denote a parallel communication port is LTP port. DOS supports three LTP ports i.e. LTP1, LTP2, LTP3 while OS/2 supports network ports from LTP4 through LTP9 too. Generally LTP4 are used for parallel printers. Thus LTP1 and LTP2 are name of the port, which are basically sets of computer resources used for parallel communication with printers.
The older BIOS versions supported two or three parallel LTP ports but the never version supports coup complete parallel ports.
Posted By :- Ajay Dussad