The Most Energy-Efficient Laser Printer in the World

Lahore 20, 2010 – HP today bolstered its LaserJet Pro printer line with new ”plug and print” technology that allows customers to begin printing in as little as Two minutes by simply connecting a net book, notebook or desktop PC to the printer With a USB cable – no CD required. New monochrome printers featuring HP Smart Install include the HP LaserJet Pro P1100 Printer series – the most energy-efficient laser printer in the world

(1) – the HP LaserJet Pro M1130/M1210 Multifunction Printer (MFP) series, the HP LaserJet Pro P1560 Printer series and the HP LaserJet Pro P1600 Printer series.  “Our customers demand easy printing and we’re giving it to them – no awkward CD-ROMs to install, no drivers to download,” said Shahid Khan, Director Marketing, Imaging and Printing Group, HP. “HP Smart Install offers the future of Printing, today.” Shahid further added, “The printers feature new Industry-first HP Auto-On/Auto-Off technology, which lets users print instantly even if the printer has gone into Auto-Off mode, allowing for reduced energy Consumption while still giving SMBs the convenience and speed needed to work Efficiently.” For desktop HP LaserJet printers, HP’s Auto-On/Auto-Off technology helps customers use up to three times less energy than in a device’s normal sleep mode,

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Now-a-days computer is playing a main role in everyday life it has become the need of people just like television, telephone or other electronic devices at home. It solves the human problems very quickly as well as accuratly. The important characteristics of a computer are described below:

1. Speed

The computer is a very high speed electronic device. The operations on the data inside the computer are performed through electronic circuits according to the given instructions. The data and instructions flow along these circuits with high speed that is close to the speed of light. Computer can perform million of billion of operations on the data in one second. The computer generates signals during the operation process therefore the speed of computer is usually measure in mega hertz (MHz) or gega hertz (GHz). It means million cycles units of frequency is hertz per second. Different computers have different speed.

2. Arithmetical and Logical Operations 

A computer can perform arithmetical and logical operations. In arithmetic operations, it performs the addition, subtraction, multiplication and division on the numeric data. In logical operation it compares the numerical data as well as alphabetical data.

3. Accuracy

In addition to being very fast, computer is also very accurate device. it gives accurate output result provided that the correct input data and set of instructions are given to the computer. It means that output is totally depended on the given instructions and input data. If input data is in-correct then the resulting output will be in-correct. In computer terminology it is known as garbage-in garbage-out.

4. Reliability

The electronic components in modern computer have very low failure rate. The modern computer can perform very complicated calculations without creating any problem and produces consistent (reliable) results. In general, computers are very reliable. Many personal computers have never needed a service call. Communications are also very reliable and generally available whenever needed.

5. Storage

A computer has internal storage (memory) as well as external or secondary storage. In secondary storage, a large amount of data and programs (set of instructions) can be stored for future use. The stored data and programs are available any time for processing. Similarly information downloaded from the internet can be saved on the storage media.

6. Retrieving data and programs

The data and program stored on the storage media can be retrieved very quickly for further processing. It is also very important feature of a computer.

7. Automation

A computer can automatically perform operations without interfering the user during the operations. It controls automatically different devices attached with the computer. It executes automatically the program instructions one by one.

8. Versatility

Versatile means flexible. Modern computer can perform different kind of tasks one by one of simultaneously. It is the most important feature of computer. At one moment your are playing game on computer, the next moment you are composing and sending emails etc. In colleges and universities computers are use to deliver lectures to the students. The talent of computer is dependent on the software.

9. Communications

Today computer is mostly used to exchange messages or data through computer networks all over the world. For example the information can be received or send throug the internet with the help of computer. It is most important feature of the modern information technology.

10. Diligence

A computer can continually work for hours without creating any error. It does not get tired while working after hours of work it performs the operations with the same accuracy as well as speed as the first one.

11. No Feelings

Computer is an electronic machine. It has no feelings. It detects objects on the basis of instructions given to it. Based on our feelings, taste, knowledge and experience: we can make certain decisions and judgments in our daily life. On the other hand, computer can not make such judgments on their own. Their judgments are totally based on instructions given to them.

12. Consistency

People often have difficulty to repeat their instructions again and again. For example, a lecturer feels difficulty to repeat a same lecture in a class room again and again. Computer can repeat actions consistently (again and again) without loosing its concentration:

• To run a spell checker (built into a word processor) for checking spellings in a document.
• To play multimedia animations for training purposes.
• To deliver a lecture through computer in a class room etc.

A computer will carry out the activity with the same way every time. You can listen a lecture or perform any action again and again.

13. Precision

Computers are not only fast and consistent but they also perform operations very accurately and precisely. For example, in manual calculations and rounding fractional values (That is value with decimal point can change the actual result). In computer however, you can keep the accuracy and precision upto the level, you desire. The length calculations remain always accurate.

Computers can also be divided into three categories depending upon their instruction and form of input data that they accept and process. These are:

1. Analog Computers
2. Digital Computers
3. Hybrid Computers

1. Analog Computers

The word “Analog” means continuously varying in quantity. The analog computers accept input data in continuous form and output is obtained in the form of graphs. It means that these computers accept input and give output in the form of analog signals. The output is measured on a scale. The voltage, current, sound, speed, temperature, pressure etc. values are examples of analog data. These values continuously increase and decrease. The analog computers are used to measure the continuous values. The thermometer is an example of analog device because it measures continuously the length of a mercury column. Another example of analog computer is the analog clock because it measures the time by means of the distance continuously covered by the needle around a dial. Similarlym speedometer, tire-pressure gauge are also examples of analog devices.

The analog computers have low memory size and have fewer functions. These are very fast in processing but output return is not very accurate. These are used in industrial units to control various processes and also used in different fields of engineering.

2. Digital Computers

The word “Digital” means discrete. It refers to binary system, which consists of only two digits, i.e. 0 and 1. Digital data consists of binary data represented by OFF (low) and ON (high) electrical pulses. These pulses are increased and decreased in discontinuous form rather than in continuous form.

In digital computers, quantities are counted rather than measured. A digital computer operates by counting numbers or digits and gives output in digital form. A digital computer represents the data in digital signals 0 and 1 and then processes it using arithmetic and logical operations. Examples of digital devices are calculators, personal computers, digital watches, digital thermometers etc. Today most of the computers used in offices and homes are digital computers. 

The main features of the computers are:

• Give accurate result.
• Having high speed of data processing.
• Can store large amount of data.
• Easy of program and are general purpose in use.
• Consume low energy.

3. Hybrid Computers
The hybrid computers have best features of both analog and digital computers. These computers contain both the digital and analog components. In hybrid computers, the users can process both the continuous (analog) and discrete (digital) data. These are special purpose computers. These are very fast and accurate. These are used in scientific fields. In hospitals, these are used to wathc patient’s health condition in ICU (Intensive Care Unit). These are also used in telemetry, spaceships, missiles etc.

Differentiate between Analog and Digital Computers

Computer is an electronic machine that is used to solve different kinds of problems according to a set of instructions given to it. Computer consists of different units that perform various functions. All the operations of the computer are controlled by the program instructions. These program instructions are known as software. A system is a group of related components that make up a body to perform a specific function. Therefore computer system is defined as:

The computer along with various units and software that performs different activities in data processing are collectively known a computer system. A computer system is divided into two sub-systems:

1. Computer Software
2. Computer Hardware

Computer Software

A set of instructions given to the computer in machine code that tells the computer what to do and how to perform the given task of the user is known as computer software.

 OR

A set of instructions given to the computer in machine code to solve problems or to control different operations of the computer is known as computer software.

the sofware is developed in computer programming languages. You can not feel, touch or see software inside the computer memory.

Computer Hardware

The physical parts of a computer are known as computer hardware. You can touch, see and feel the hardware. The hardware consists of electronic circuits and mechanical equipment etc. used to perform various functions in the computer. The hardware components are:

1. Input devices
2. Output devices
3. Central Processing Unit (CPU)
4. Memory unit
5. Storage devices

Components of Computer

The internal architechtural design of computers differs from one system model to anohter. However the basic components and their functions are same for all computer systems. The construction of a typical comupter (PC) is very simple. It contains different components. Each components performs a specific function in the computer.

Input Devices

The devices that are used to enter data and instructions into the computer are called input devices or units. In old computers the punched card readers, paper tape readers were used as input devices. Now-a-days the most commonly used input devices are Keyboard and Mouse.

Output Devices

The computer processes the given input data and gives the output. The devices that are used to get output from a computer in readable from are called output devices. A number of output devices are available. Some commonly used output devices are video display units (VDU) and printers.

Central Processing Unit

Central Processing Unit is simply called as CPU. It is the main components of the computer and it is also called the Processor. The processor used in microcomputer is referred to as Microprocessor. CPU is considered the brain of the computer. It performs all operations of data according to program’s instructions. It executes the program instructions and tells other parts of the computer what to do. The CPU fetches instructions of program from main memory and executes them one by one. The CPU also has the ability to decide which instruction will be executed next. The speed of the CPU is measured in Mega Hertz (MHz) or Giga (or more).

The CPU is divided into two main prart of sub-units. These are:

1. Control Unit (CU)
2. Arithmetic Logic Unit (ALU)

1. Control Unit (CU)

The control unit is the most important component of the CPU. It controls and coordinates the activities of all the other units of the computer. The control unit is considered as the logical hub of the computer. It acts as a central nervous system for the other components of the computer.

For example the control unit receives the data and instructions from the input device and stores them in the main memory. It performs all these functions by issuing commands to the relevant unit of the computer.

The control unit also controls the execution of instructions given to the computer. It fetches the instructions and data from the memory unit. It decodes and executes the instructions one by one.

2. Arithmetic Logic Unit (ALU)

Arithmetic Logic Unit or simply ALU is another important component of CPU. It performs the arithmetic and logical operations on the data. When the control unit encounters and instruction related to perform arithmetic or logical operation on data, it passes that instruction to ALU.

• In arithmetic operations ALU performs the addition, subtraction, multiplication and division.
• In logical operations ALU compare the numerical data as well as alphabetic data. For example, it checks whether first number is greater than second, less than second or equal to second etc. It must be noted that some of the logical operations can be done on test data. For example when you want to search a word in a document., the CPU matches each word of the docum ent with the given word. Actually the ALU compares each word of document with the given word through relational equal operator (=).

The ALU consists of a number of registers and adder circuits. A register is a temporary storage device which holds data and instruction as long as it is being interpreted (decoded) and executed. When the data and instructions are fetched from main memory for processing, these have to be stored in one of the registers of the CPU.

Microprocessor

The processor used in microcomputer is referred to as Microprocessor. Today microprocessor used in microcomputer designed in a single chip and fits into a special socket on the motherboard. The most fundamental part of the the mothermoard is the microprocessor chip. In personal computers two types of microprocessors are useed. These are:

i) Inter Microprocessor

This microprocessor made by Intel Corporation is commonly used in microcomputers. You can say that 90% microcomputers use this type of microprocessor. Actually the Microsoft Windows operating system is developed to run on Intel microprocessor. Inel company has marketed its microprocessors under the names Pentium, Pentium Pro, Pentium II (P2), Pentium III (P3), Pentium IV (P4), Core 2 Due (C2D) etc.

Today the most advanced microprocessor chip of Intel is C2D. Many ads for PCs contain the logo “Intel Inside” to show that the systems run an Intel microprocessor.

ii) Motorola Microprocessor

Motorola microprocessor is made by Motoroal. It is used in personal computers of Apple. Macintosh operating system is developed to run on Motoroal microprocessor.

Coprocessor

A coprocessor is a special additional processor chip that helps the processor of a computer in performing specific thasks. The math-coprocessor is an example of coprocessor. In modern computer math-coprocessor is specifically used to perform very large and complex mathematical calculations. The math-coprocessor is also known as floating-point cocoprocessor or numeric-coprocessor. The computers having cocoprocessors are used for engineering, scientific and graphic applications.

RAM stands for Random Access Memory. Actually the main memory or primary storage is referred to as RAM. It consists of memory chips that can be read from and writtern to by the processor. When the computer is powered on, certain operating system files load into RAM from the storage device such as a hard disk. Then operating system remains in RAM as long as the computer has continuous power.

The control unit performs the following functions for main memory.

• Stores the data and instructions (entered from input unit) into the RAM (or main memory).
• Provides the data and instructions from main memory to other parts of the computer.
• Stores the processed results back into the RAM (or main memory).

The RAM plays very important role in data processing. The program and the data must be transferred to RAM before to run the program to process the data. The processor processes the data according to the program instructions by fetching the data and instructions from the RAM. The processor interprets and executes the program instructions while the program is in RAM. During this time the content of RAM may change. RAM can hold multiple programs simultaneously, provided the computer has enough RAM to accommodate all the programs. The program with which you are working usually is displayed on the screen. In Windows environment you can switch from one program to another.

 The storage capcity of RAM or main memory is measured in bytes. A byte is a group of 8-bits. One character takes one byte of memory. The amount of data and program size are also measured in bytes.

The large RAM size increases the accessing speed of the computer. RAM plays an integral part in the internal operation of processor. Microcomputers come with different amounts of RAMs which are from 128MB to 2GB. Advertisements normally list the type of processor, the clock speed of the processor and the amount of RAM in the computer. More RAM means the computer can use powerful program with large size. It also improves the data processing speed of the computer.

Memory Module

RAM chip is smaller in size than the processor chip. A RAM consists of more than one chips. RAM chips usually reside on a memory module which is a small circuit board. Memory slots on the motherboard hold memory modules. There are three types of memory modules. There are:

1. DRAM

DRAM stands for Dynamic Random Access Memory. DRAM is the most common type of RAM used to store data & instructions. In order to maintain data in DRAM chip, the chip is refreshed frequently (hundreds of time a second), otherwise data may be lost. During the refreshing process the CPU has to wait to read & write data in DRAM. It is because DRAM decreases the processing speed of the computer.

Today many DRAM chips exists and most of which are faster than the basic DRAM. The most important are:

SDRAM

SDRAM stands for Synchronous Dynamic RAM. SDRAM are much faster than basic DRAM chips because they are synchronized to the system clock. Often in computer ads, the speed of SDRAM is expressed in megahertz (MHz).

RDRAM

RMRAM stands for Rambus Dynamic RAM. It is faster and more expensive than SDRAM because it uses pipelining technique. It is used in Intel P4. Today most of PCs use SDRAM or RDRAM.

2. SRAM

SRAM stands for Static Random Access Memory. It is faster than DRAM because it does not have to be refreshed frequently and the CPU has not to wait to read & write data. SRAM chips however are more expensive than DRAM chips. Special applications such as cache use SRAM chips.

ROM stands for Read Only Memory. The ROM contains instructions that are permanently stored by the manufacturers when they manufacture the chips. In fact recording data and instructions permanently into this kind of memory is called “burning in the data”. The instructions stored in ROM can only be read but cannot be modified. This is the reason why it is called Read Only Memory.

ROM is a semiconductor chip programmed at the time of its manufacture and is not re-programmable by the user. The programs stored in ROM are called firmware. It is a non-volatile memory. The contents of ROM are not lost when the computer is turned off.

The ROM contains the Basic Input / Output System (BIOS which is a set of instructions that are automatically activated when the computer is turned on. It means that computer uses the instructions of ROM at the time of booting for the following purposes.

• To check different units of computer system.
• To load the operating system into computer memory etc.

Many other devices also contain ROM chips. For example a printer has a ROM chip that contains data or information for fonts. You can say that each electronic device has ROM chip that contains information about that device.

The ROM is further divided into:

1. PROM
2. EPROM
3. EEPROM

1. PROM

PROM stands for Programmable Read Only Memory. PROM is a blank ROM chip on which the user can write his own program instructions and data but only once. However once the program or data is written in PROM chip, it cannot be changed. The programmer uses micro-code instructions to write information in a PROM chip. Once the programmer writes the micro-code on the PROM chip, it functions like a normal ROM chip.

2. EPROM

Once ROM or PROM is programmed, its contents cannot be changed. However there is another type of memory chip called EPROM that overcomes this problem.

EPROM stands for Erasable Programmable Read Only Memory. It is another important form of read only memory. Like PROM, it is initially blank and the user or manufacture can writes his own program or data by using special devices. Unlike PROM the data written in EPROM chip can be erased by using special purpose devices and ultraviolet rays. So program or data written in EPROM chip can be changed and new data can also be added on this form of ROM. When EPROM is in use, its contents can only be read.

3. EEPROM

EEPROM stands for Electrically Erasable Programmable Read Only Memory. This kind of ROM can be re-written by using electrical devices and so data stored on this ROM chip can be easily modified.

The motherboard is the main circuit board of the system unit. It is also referred to as system board. Many electronic components are connected to the motherboard and some components are built into it. The processor chip and memory chips are plugged (installed) into the motherboard. The motherboard contains sockets or slots in which electronic components are installed. You can say that motherboard is the master circuit board in a computer.

CMOS

CMOS stands for Complementary Metal Oxide Semiconductor. It is similar to RAM and is a high-speed but it is non-volatile memory. It uses batter to reatin information even when the power to the computer is off. The contents of CMOS can be changed very easily.

CMOS is a special type of memory, which stores the configuration information about the computer such as information about type of disk drives, keyboard, monitorm system current date and time, password, system startup information etc.

Cache Memory

Data and program instructions are moved from RAM to CPU’s registers during data processing. It is most time consuming method and CPU has to waste a lot of time ot access data from memory.

Cache memory is similar to RAM but it is extremely fast than RAM. It is normally used between RAM and CPU. Cache speeds up processing speed of computer because CPU stores frequently used instructions and data in it. When the program is running and the CPU needs a specific data or program instructions, the CPU first checks it in cache memory. If the data is not there, the CPU reads the data from RAM into its registers, but it also loads a copy of the same data or instruction in cache memory. The next time the CPU uses it if required again and saves the time needed to load it from RAM.

Epansion Slot

PC motherboard has two or more expansion slots used to add new components to the computer. The slots hold adapter card also called expansion card. The adapter card provides connections to peripherals. A peripheral is a device that connects to the system unit and is controlled by the CPU. Examples of peripherals are modem, disk drive, printer, scanner, keyboard, mouse etc.

The memory (RAM) chips are also inserted into the expansion slot to expand the size of memory. Similarly network interface card is inserted expansion slot to connect the computer to network and so on.

The types of adapter cards with their functions are given below.

Accelerator Card
It is used to increase the speed of processor.

I/O Card
It is used to connect input/output devices such as printer, mouse keyboard etc.

Game Card
It is used to connect joystick.

Disk Controller Card
It is used to connect disk drives.

Modem Card
It is used to connect other computers through telephone line or cable television line.

Network Card
It is used to connect other computers and peripherals in local area network.

PC-to-TV Connector Card
It is used to connect a television.

Sound Card
It is used to connect a speaker or microphone.

TV Tuner Card
It is used for viewing television channels on the computer monitor.

Video Card
It is used to connect a monitor.

In modem computer, motherboard includes all necessary capabilities and don’t require adapter cards. For example, sound and video functions may be built into the mother board.

In the past, it was very difficult job to install a card. The computer technician had to set switches and other elements on the motherboard. Now-a-days, computers have plug and play capabilities. It means that a computer automatically can configure adapter card when it is installed into it. In these computers, you can easily plug in a device and turn on the computer. The device is ready to use (It means device is ready to play its role).

Computer Buses

We know that data and instructions inside the computer are stored and moved from one unit to another in the form of bits. Actually the bits are moved in the form of electric pulses. Therefore, computer bus is defined as:

The electric paths through which computer (CPU) sends and receives data and instructions (and also sends command signals) to and from different components of computer are called computer buses.

The computer bus is backbone of the computer and computer cannot perform any function without it. The computer bus is like electric wiring used to create circuits. However computer buses are used to connect devices with the CPU.

Typically a bus consists of 40 to 150 electric wires or lines running parallel to each other. One line can carry one bit at a time. The capacity of a computer bus depends on the number of data lines it contains. For example a bus with 16 lines can transfer 16 bits at a time.

In the past the performance of computer buses was measured by the number of bits they could transfer at one time. Hence, the newest 64-bit buses are typically considered the fastest for data transfer. However performance of buses was measured according to their data transfer rates. It was measured in Mbps (Megabits per second).

Today data transfer rate of a computer bus is measured in MHz. Every bus also has a clock speed, just like the processor. The clock speed for a computer bus is measured in hertz (Hz). Most of today’s processor have a computer bus clock speed from 100 MHz to 400 MHz (one Mega Hertz is equal to one million ticks per second). The higher the computer bus clock speed, the faster the transmission of data. It means that due to higher the computer bus clock speed, application running and data accessing speed will be very fast.

A computer has two basic types of buses. These are:

1. Expansion buses
2. System buses

Expansion Buses
Expansion buses are also referred to as External Buses. These buses connect the external devices such as keyboard, mouse, modem, printer etc. to the processor. Expansion buses allow the processor to communicate with the peripherals. We connect a peripheral with the system unit through a port on an adapter card, which is inserted into an expansion slot on the motherboard.

The basic types of expansion buses are:

ISA Bus
ISA stands for Industry Standard Architecture. It is most common and slowest bus used to connect mouse, model card, sound card and low-speed network card.

PCI Bus
PCI stands for Peripheral Component Interconnect. PCI is a high-speed local bus used to connect video card, sound card and high-speed network card. This bus transfers data about four times faster than the ISA bus. Today most of the PCs have a PCI bus as well as ISA bus.

AGP Bus
AGP stands for Accelerated Graphics Port. AGP bus is specially designed by Intel to improve the transmission speed of video and 3-D graphics. The AGP bus provides a faster, dedicated interface between the video card and memory.

USB
USB stands for Universal Serial Bus. In a computer with a USB, USB devices can be connected to each other outside the system unit and then single cable attaches to the USB port. The USB port then connects to the USB, which connects to the PCI bus on the motherboard. This bus eliminates the need to install cards into the expansion slots.

System Buses
The system buses are also called the Internal Buses. The system buses are the part of motherboard and connect the processor to the main memory as well as other devices that reside on the motherboard. The system buses are classified according to their functions as:

1. Data bus
2. Address bus
3. Control bus

1. Data Bus
The electric path through which the contents of data (or actual data) are transferred from one unit to another is called Data Bus. Actually the data bus is a group of parallel wires. The number of wires in the bus affects the speed at which data can transfer from one component of computer to another. Each wire can transfer one bit of data at a time. A data bus with 8 wires can transfer 8 bits (one byte) of data at a time. The modern PCs have 64-bit data bus and can transfer 8 bytes of data at a time. The data bus connects the CPU, memory unit and other hardware devices on the motherboard.

2. Address Bus
We know that the components of computer are connected to one another through the system bus. So it is important to assign a unique ID to each component. This ID is called the address of that component. Therefore the computer bus, which is used to identify different components of a computer as well as to specify the address of different memory locations is called address bus. For example when a computer component wants to communicate with other component, it specifies the address of the destination component. Similarly when CPU wants to write some data at memory location 932, it places the address of main memory and the address of location i.e., 932, on the address bus. When the main memory sees its address on the address bus, it reads the data from the data bus and writes it to the specified location within the main memory.

The capacity of address bus depends upon the number of its wires. If the address bus has 8 wires then CPU can address 256 bytes of memory, i.e. 2⁸ = 256. Now-a-days most CPUs have 32-bit address buses can address 4 GB of memory.

3. Control Bus
The electric path through which the control unit sends out control signals (commands) to control the sequence of operations that take place while a program is being executed, is called control bus. For example, the control unit directs the transfer of data from the main memory to the ALU for arithmetic or logical operations. Similarly data flow between secondary memory and main memory is controlled by the control unit through this bus.

The control bus directly connects the CPU, main memory and I/O ports. We know that many system devices are connected to the data bus but only one of these is enabled at a time. The CPU provides the enabling signal through the control bus lines. For example if the CPU wants to read data from the port attached to the keyboard, it will perform this activity as follow:

• sends out the address of keyboard port on the address bus.
• enables keyboard port by sending a signal to it on a control bus line.
• reads the data from the data bus. The data is put on it by the port.

Ports

Power Supply

Power supply is an electrical component inside the system unit that converts the A.C power into D.C power. Power Supply supplies the correct voltage or power to all parts of the comptuer. It is a simple electrical system, which takes 240 or 110 A.C voltages and converts them into D.C voltages of 3V, 6V, 12V and 24V. The D.C voltage is required to operate different components of a comptuer.

Some exterals peripherals such as an external modems, speakers etc. have an A.C adapter, which converts the A.C power into D.C power that the peripheral requires.

The input, ouput and communication devices are connected to the system unit through a special device called the port. It is an interface or connecting socket on the outside of system unit. It provides a standard way of communication between the computer and its input and output devices. For example, keyboard, mouse, monitor, printer, modem etc. come with a cable and a multiple connector. The device is linked with the computer by plugging its connector into a port. The term jack sometimes is used to identify audio and video ports.

The back of the system unit contains many ports. Some modern PCs also have ports on the front of the system unit. Ports have different types of connectors. A connector joins a cable to a device or peripheral. One end of the cable attaches to the connector on the system unit and the other end of the cable attaches to a connector on the device. The connectors are available of two types.

For example, a printer port might use 25-pin female connector or 36-pin female connector etc.

Types of Ports

A system unit may contain many ports of different types. The main type of ports are serial port, parallel port and USB port. Most personal computers have at least one serial port, one parallel port and two USB ports. The types of ports are described below.

1. Serial Port

A serial port provided a connection  for transmitting data one bit at a time. The data is serial port is transmitted one bit at a time through a single wire. However the serial port consists of multiple wires. The other wires control the flow of data. The COM port (communication port) on the system unit is one type of serial port. The IBM computers have maximum four serial ports, which are designated COM1, COM2, COM3 and COM4.

The transmitting of data through serial port is very slow because data is transmitted one bit at a time. The mouse, keyboard, modem etc. are connected to serial port. Modem is connected to the serial port because data through telephone line is communicated in a specific frequency.

Serial ports conform to either the RS-232 or RS-422 standard, which specifies the number of pins used on the ports connector. Two common connectors for serial ports are 9-pin male connector and 25-pin male connector.

2. Parallel Port

A parallel port provides a connection for transmitting data 8-bits at a time. The devices that are connected to the parallel port have a data cable with eight parallel separate data lines. The printer is connected to the parallel port. The cables used to connect printer to the computer through the parallel port often have 25-pin female connector. The IBM computes have maximum 3 parallel ports, which are designated LPT1, LPT2, LPT3. In most microcomputers LPT1 port is used as a standard parallel port. The transmitting of data through parallel ports is faster than serial port.

3. USB Port

USB stands for Universal Serial Bus. Today it is the most popular standard port used in PCs of both IBM compatible and Apple computers. The USB allows upto 127 devices to be connected to the bus via a single port. Today personal computers typically have 2 to 4 USB ports either on the front or back of the system unit. The USB hub is also available to connect multiple devices with a computer having a single USB port. A USB hub is a device, which is plugged into a USB port on the system unit and contains multiple USB ports into which you can plug multiple devices.

USB port also supports hot plugging and plug & play. It means that you can attach devices with a computer while computer is running. You have not to restart the computer after attaching the device.