Extension slots and Ports

Extension slots expand the capabilities of computer. These are slots that allow new and enhanced feature to be added by you.


Expansion slots can be categorized into three different categories: ISA, PCI, and AGP.

(i) ISA (International Standard Architecture): are the old slowpoke (16 bits) connectors. They have very low data transfer speeds and interrupt the processor frequently while transferring. They are problematic in install and use up scarce processor interrupt request lines.

(ii) PCI (Peripheral Component Interconnector): PCI are the current standard for interface cards. They transfer relatively higher amounts of data (32 bits) compared to ISA slots. They can share interrupt lines and are easier to configure. Networks, SCSI, sound and video cards make use of PCI slots.

(iii) AGP (Accelerated Graphics Port): AGP is a special kind of double speed PCI slot. It is designed especially for graphic cards, allowing them to transfer data at up to 512MB per second. AGP cards can use main memory as an extension of it’s on board memory. Video cards use AGP slots. It contains ADC (Analog to Digital Converter) which receives information from the local memory and controls the intensity of red, blue and green electron beams.

Function of AGP:

(a) Perform image calculation

(b) Generate pixels

(c) Convert graphical commands into a data stream and keep in the local memory.

(d) Controls intensity of colors.

Input /Output Ports


Input and output ports are the most basic routes of information exchange. Most motherboards include these ports in their circuitry. The various types of ports that you could find on a new motherboard are:

(a) COM ports: COM ports are the serial interface for computers transferring 1 bit of data at a time. They are slow but reliable and serial lines can carry data over long distances. These ports are normally used to connect a Modem.

(b) Parallel ports: These ports are dedicated for faster data transfer Parallel ports carry 8 bits of data at a time and are faster than serial ports, but they can carry data over very short distances and become unreliable after a few meters. Printers are usually connected to parallel ports. These ports are also called Centronic interface because first time printer manufacturer company (Centronic) used these port for printers to attach printer in IBM PC which have already 25 pins parallel ports. In this way, IBM has developed it first time to attach Centronic printer.


  • SPP (Standard Parallel Port): IBM offered bi-directional parallel port when PS / 2 operating system was introduced in 1987. Bi-directional communication allows each device to receive data as well as transmit it. Many devices uses eight pins (2 to 9 pins) originally designed for data. The standard parallel port is capable of sending 50 to 100 kilobytes of data per second.
  • EPP (Enhanced Parallel Port): EPP was designed by Intel, Xircom, and Zenith in 1991. EPP allows for much more for data, 500 Kilobytes to 2 megabytes, to be transferred for non-printer devices that would attach to the parallel port, particularly storage devices that needed the highest possible transfer rate.
  • ECP (Extended Capabilities Port): Microsoft and Hewlett Packard jointly announced ECP in 1992 for improved speed and functionality for printers.

(c) USB (Universal Serial Bus) ports: These ports have higher data transfer rate than serial ports. USB ports is the new standard for transferring serial data up to 12 MB per second and are used to connect Monitors, Scanners, Keyboards mouse, speaker, printer modem etc. The connecting of a USB devices to the computer is very simple. These connectors are available at the back side of your computers.

(d) SCSI: SCSI (pronounced as skuzzy) is a high speed interface for connecting serial devices, both internal and external. Primarily used for connecting hard disks. You could also connect scanners, CD-ROM drives and Zip drives. SCSI is divided into three categories: SCSI-1, SCSI-2, and SCSI-3.

(e) Infrared: Infrared are ports that don’t need cabling or connectors. They use Infrared light to communicate between devices like TV or Video Remote. These ports are normally found on Laptops, palmtops etc.

(f) Bluetooth: Bluetooth is a low cost, low-power, wireless radio frequency technology that allows various electrical devices to communicate with each other. These devices operate in the 2.4 GHZ ISM (Industrial, Scientific, Medical) band. One of the advantage of Bluetooth over IrDA(Infrared Data Association) is that close proximity between the communicating devices is not required, distance of up 10 meters or 32 feet are allowed. Also, Bluetooth does not suffer from any line of sight (omni directional) restrictions. The Bluetooth is an industrial specification for wireless personal area networks (PANs).

It provides a way to connect and exchange information between devices like as PDAs (Personal Digital Assistants), mobile phone, laptops, PCs, printers and digital camera. The Spec was developed by Ericsson, later formalized by the Bluetooth Special Interest Group (SIG). The Bluetooth wireless technology comprises hardware and software and interoperability requirements.

Beyond unleashing devices by replacing cables, Bluetooth wireless technology provides a universal bridge to existing data networks or peripherals interface, and a mechanism to form small private ad, hoc groupings of connected devices away from fixed network infrastructures.

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