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Computer Science


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THE MOTHERBOARD (also called System Board or Circuit board).

Computers, like all electronic circuit devices are made of printed Circuit boards (electronic boards on which copper wires have been printed to form circuit paths).

The Motherboard is the main part (large circuit board) of your computer that every thing else plugs into.

It is usually a sheet of olive green or brown fiberglass with several thin gold lines on it and chips sticking off it.

By itself, the Motherboard is just an empty plate.  It’s the hardware that sits on it that does the work.  On it, we have the CPU, SIMM sockets, BIOS and slots. 

The Motherboard provides a convenient method of inter-board connection.  It is where all electronic components such as the Microprocessor, Memory chips, Interface chips, and Bus connections are assembled.

The motherboard also contains a no. of expansion slots in which Interface cards are slotted (plugged in).

The little gold lines are called Buses and act as roadways of information between all these features.  The buses enable the parts to communicate and perform the functions of your computer.


A Port is a connection or socket used to connect a device, such as a Printer, Monitor, Mouse, Scanner, etc to your computer.

I/O Ports are the sockets found at the back of your computer where you can connect external computer devices to the interface cards inside the computer.  They allow access in & out of the computer for cables. 

There are several types of external ports: –

  1. Parallel (LPT) ports.
  2. Serial (Com) ports.
  3. USB ports.
  4. SCSI ports.


The standard PC parallel port was originally designed for sending information to Printers or Scanners.  That is the reason why they are sometimes referred to as Line Printer Terminal (LPT) ports

They are D-shaped with holes for 25 pins. 

It is used mainly to connect Printers, Scanners, and sometimes external Hard drives, CD-ROM drives, Tape devices & Network adapters to your computer.

Parallel ports transmit data using an 8–bit parallel interface & are therefore, used for devices that accept information 8 bits at a time.  They transmit data byte-by-byte.  They are usually faster than Serial ports.

Note.  The SCSI Port is an example of a parallel port.


They are sometimes referred to as Communication (COM) ports.

Are also D-shaped with 9 or 25 pins.

They are used primarily to connect devices such as serial Mice, external Modems, and sometimes Printers to the System unit.  They can also be used for computer-to-computer connection.

The Serial port has 2 data lines, one for data in & the other for data out. 

Transmission rates of Serial ports are slower than those of Parallel ports.  This is because, Serial ports transmit data bit-by-bit.  Therefore, they are used for devices that accept information 1 bit at a time (or for devices that are a bit slow).


Many new PCs come with USB ports.  USB ports support a wide range of desktop peripherals, e.g., Keyboards, digital Cameras, etc. 

USB combines the best features of SCSI architecture with an advanced Plug-and-play standard.  It replaces the traditional Serial & Parallel ports with a single port that is extensible through the use of hubs and devices daisy-chained in a tree arrangement.

USB was designed to deliver a data transfer rate of up-to 12Mbits/sec to & from the PC.  It also supports low-speed mode of 1.5Mbit/sec for devices like Keyboards, Mice and Joysticks.

USB is “user-friendly

Advantages of USB ports over Serial & Parallel ports.

  • Devices are powered by the bus – there is no need for external power adapters.  USB allows unpowered devices to draw up to 500 mA over the connector cable.
  • Can support a max. of 127 daisy-chained devices, because of its high bit addressing system.

SCSI (Small Computer Systems Interface) PORTS.

Pronounced as Scuzzy.

SCSI is a device interface used by PCs, Apple Macintosh computers and many UNIX systems. 

Small Computer System Interface (SCSI) card is used for attaching to peripheral devices that require high speed data transfers between the device and memory. 

The SCSI cards provide parallel high-speed data transfer in the range of 10 MB/s to the memory. 

It connects peripherals to your computer via standard hardware interface, which uses standard SCSI commands.


The basic Microcomputer system consists of the Motherboard, the Power Supply unit, Hard disk & Floppy disk drives, I/O interface cards, Disk controller card, Video card, optional CD-ROM drive, Sound and Network interface cards.

All these components are housed in a cabinet (or Chassis).  The cabinet has rear connectors for peripheral devices through the motherboard or interface cards.

The Interface cards are usually plugged into the microcomputer’s card slots with power-supply voltages and bus signals distributed to the card slots.

Cables then go from connectors on the interface cards to the peripheral devices.

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