Block diagram of a typical microcomputer is shown below
Input Unit:
This unit is used to give input to the computer. The input can be given to the computer through various ways. This determines the media. In the earlier days rectangular punched cards were used to give input. Now a days the common way to give input through the keyboard. Mouse is also becoming a famous input device which is used to give graphical data.
Control Unit:
The control unit controls the other units such as arithmetic logic unit, memory unit to carry out instructions.
Memory Unit:
The instructions and data used in the computer are stored in the memory unit. They are retrieved as and when required by the control unit to do other operations.
Arithmetic Logic Unit:
The arithmetic and logic unit does the arithmetic operations like addition, subtraction and logical operations such as comparisons and many other operations.
Output Unit:
This unit is used to get processed information from the computer. Solved output devices are used for getting the output; common one is monitor and printer.
Memory in the computer is broadly divided into
Main memory (Primary memory)
Secondary memory
The main memory holds all data, instructions, and results temporarily. The memory consists of hundreds of thousands of cells called ‘storage locations’ each capable of storing one word of information. The purpose of secondary memories is to retain data and program for future use.
Main memory:
For main memory relatively high speed memories like semi-conductor memories were used. But for the secondary memories magnetic memories were used because of their low speed, high storage capacity and low cost.
Semi conductor memories includes RAM, ROM, PROM, EPROM and EEPROM.
RAM – Random Access memory (Read/Write Memory)
ROM - Read Only Memory
PROM - Programmable Read Only Memory
EPROM - Erasable Programmable Read Only Memory
EEPROM - Electrically Erasable Programmable Read Only Memory
Secondary Memory:
Secondary Memories includes Floppy disk, Hard disk, Magnetic Tape, and Compact disk.
Floppy Disk:
The most common storage medium used on small computers today is a floppy disk. It is a flexible plastic disk coated with magnetic material. Information can be recorded or read by inserting it into a disk drive connected to the computer. The disks are permanently encased in stiff paper jackets for protection and easy handling.
Different standard size and different storage capacity of floppy disks are available in 8 inch, 5 ¼ inch, 3 ½ inch and 360 KB, 1.2 MB, 1.44 MB respectively.
Hard disk:
To storage large amount of information hard disk is used, it is also known as ‘winchester disk’. A hard disk consists of two or more magnetic plates fixed to a spindle, one below the other with a set of read/write heads. The disk pack is permanent by sealed inside a casting to protect it from dust and other contaminations, thus increasing its operational reliability and data integrity. In various capacities this is available like 40MB, 80MB, 120MB, 200MB, 260MB and 560MB. According to this capacity the disk the cost also vary.
Some advantages of hard disk is
Fast read/write speed
They can capable of storing huge amount of information.
Hard disks are not susceptible to dust and static electricity.
Magnetic tapes:
Very high storage capacity at a relatively lower cost. A standard 2,400 feet tape can store about 40 million characters and can be read at a speed of 1,60,000 characters per second. It is a sequential device and therefore one has to read all the previous records to reach a particular one. They are mainly used as back up storage.
Input devices:
Input devices present data to the processing unit in machine-readable form. The keyboard is a common input device for a small computer. System may support one or more of the input devices. They are
Keyboard
Mouse
Magnetic ink character recognizer (MICR)
Optical character reader (OCR)
Joy-stick
Light pen
Digitizer
Scanner
Micro phone
Punched card reader
Punched tapes
Keyboard:
Keyboard is mainly used input device. Keyboards are of different varieties depending on the number of keys on them. 81/84 key keyboards are used in PCs and PC/XTs. 101 key keyboard used for PC/ATs. Usually the keyboard consists of four parts.
Alphanumeric keys
Special function keys
Cursor control keys
Numeric keys
Output devices
Output devices receive information from the CPU and present it to the user in the desired form. List of some output devices shown below.
Monitor
Printer
Plotter
Speaker
Monitors:
Monitor is an output device. It is the most commonly used interactive peripheral. It consists of a keyboard and a CRT, with a processing circuit. Sometimes a VDU is a simply a terminal. A VDU mostly used in the multi-user environment.
There are two types of monitor namely,
Monochrome monitor
Colour Monitor
Monochrome monitor provides only one color on the other hand color monitors have wide range of colors. The quality of monitors is often judged by the resolution (pixels/inch).
Monitors are equipped with a display card. There are varieties of display card available. Some of there are.
MDU – Monochrome Display Adapter
HGA – Hercules Graphics Adaptor
CGA – Colour Graphics Adapter
EGA – Enhanced Graphics Adapter
VGA – Video Graphics Adapter
SVGA – Super Video Graphics Adapter
The size of the monitor may be different for different monitors. Standard sizes are 15 inches to 18 inches.
The character displays in a monitor is often limited by the size is 80 characters and totally 20 row in will be displayed at time in the screen.
Printers:
Printers can be broadly be subdivided into two categories;
Impact printers
Non-impact printers
Impact Printers:
Impact printers can be described as printers which utilizes some from of striking device to transfer ink from an inked ribbon onto the paper being printed to form images or characters. Some of other printer falls into this category are,
Dot Matrix
Chain printer
Drum Printer
Daisy Wheel Printer
Non-Impact printers:
Main concept of non-impact printer is no direct contact between printer head and the paper. But in the Impact printer case, direct contact between printer head and the paper. Some of the important non-impact printers available in market are,
Laser Printer
Ink Jet Printer
Thermal Printer
Electro Static Printer
Non-Impact printers are comparatively high cost and the quality of output is also high. Speeds of these printers are high.
Plotters:
Plotters are used to produce output containing graphics or diagrams. With the availability of multi-colour plotters, they are increasingly used for preparing financial documents, annual reports and engineering drawings. Three types of plotters are available. They are,
Drum plotters
Flat bed plotters
Injection plotters
In the drum plotter, both paper and pen move, i.e. Paper move up and down in the rollers, the pen move left and right in the bar so that, the graphics picture is created.
In the flat bed Plotter, paper is fixed in the drawing pad, the pen is fixed in the bar just up to the drawing pad. To create drawing in the paper, pen bar move left to right, and pen move up and down in the bar on the paper.
In the Injection Plotter, ink nozzle sprays the ink with different colors and is able to produce large drawings containing many colors. Quality of the drawing from the Injection plotters in high as its price.
This unit is used to give input to the computer. The input can be given to the computer through various ways. This determines the media. In the earlier days rectangular punched cards were used to give input. Now a days the common way to give input through the keyboard. Mouse is also becoming a famous input device which is used to give graphical data.
Control Unit:
The control unit controls the other units such as arithmetic logic unit, memory unit to carry out instructions.
Memory Unit:
The instructions and data used in the computer are stored in the memory unit. They are retrieved as and when required by the control unit to do other operations.
Arithmetic Logic Unit:
The arithmetic and logic unit does the arithmetic operations like addition, subtraction and logical operations such as comparisons and many other operations.
Output Unit:
This unit is used to get processed information from the computer. Solved output devices are used for getting the output; common one is monitor and printer.
Memory in the computer is broadly divided into
Main memory (Primary memory)
Secondary memory
The main memory holds all data, instructions, and results temporarily. The memory consists of hundreds of thousands of cells called ‘storage locations’ each capable of storing one word of information. The purpose of secondary memories is to retain data and program for future use.
Main memory:
For main memory relatively high speed memories like semi-conductor memories were used. But for the secondary memories magnetic memories were used because of their low speed, high storage capacity and low cost.
Semi conductor memories includes RAM, ROM, PROM, EPROM and EEPROM.
RAM – Random Access memory (Read/Write Memory)
ROM - Read Only Memory
PROM - Programmable Read Only Memory
EPROM - Erasable Programmable Read Only Memory
EEPROM - Electrically Erasable Programmable Read Only Memory
Secondary Memory:
Secondary Memories includes Floppy disk, Hard disk, Magnetic Tape, and Compact disk.
Floppy Disk:
The most common storage medium used on small computers today is a floppy disk. It is a flexible plastic disk coated with magnetic material. Information can be recorded or read by inserting it into a disk drive connected to the computer. The disks are permanently encased in stiff paper jackets for protection and easy handling.
Different standard size and different storage capacity of floppy disks are available in 8 inch, 5 ¼ inch, 3 ½ inch and 360 KB, 1.2 MB, 1.44 MB respectively.
Hard disk:
To storage large amount of information hard disk is used, it is also known as ‘winchester disk’. A hard disk consists of two or more magnetic plates fixed to a spindle, one below the other with a set of read/write heads. The disk pack is permanent by sealed inside a casting to protect it from dust and other contaminations, thus increasing its operational reliability and data integrity. In various capacities this is available like 40MB, 80MB, 120MB, 200MB, 260MB and 560MB. According to this capacity the disk the cost also vary.
Some advantages of hard disk is
Fast read/write speed
They can capable of storing huge amount of information.
Hard disks are not susceptible to dust and static electricity.
Magnetic tapes:
Very high storage capacity at a relatively lower cost. A standard 2,400 feet tape can store about 40 million characters and can be read at a speed of 1,60,000 characters per second. It is a sequential device and therefore one has to read all the previous records to reach a particular one. They are mainly used as back up storage.
Input devices:
Input devices present data to the processing unit in machine-readable form. The keyboard is a common input device for a small computer. System may support one or more of the input devices. They are
Keyboard
Mouse
Magnetic ink character recognizer (MICR)
Optical character reader (OCR)
Joy-stick
Light pen
Digitizer
Scanner
Micro phone
Punched card reader
Punched tapes
Keyboard:
Keyboard is mainly used input device. Keyboards are of different varieties depending on the number of keys on them. 81/84 key keyboards are used in PCs and PC/XTs. 101 key keyboard used for PC/ATs. Usually the keyboard consists of four parts.
Alphanumeric keys
Special function keys
Cursor control keys
Numeric keys
Output devices
Output devices receive information from the CPU and present it to the user in the desired form. List of some output devices shown below.
Monitor
Printer
Plotter
Speaker
Monitors:
Monitor is an output device. It is the most commonly used interactive peripheral. It consists of a keyboard and a CRT, with a processing circuit. Sometimes a VDU is a simply a terminal. A VDU mostly used in the multi-user environment.
There are two types of monitor namely,
Monochrome monitor
Colour Monitor
Monochrome monitor provides only one color on the other hand color monitors have wide range of colors. The quality of monitors is often judged by the resolution (pixels/inch).
Monitors are equipped with a display card. There are varieties of display card available. Some of there are.
MDU – Monochrome Display Adapter
HGA – Hercules Graphics Adaptor
CGA – Colour Graphics Adapter
EGA – Enhanced Graphics Adapter
VGA – Video Graphics Adapter
SVGA – Super Video Graphics Adapter
The size of the monitor may be different for different monitors. Standard sizes are 15 inches to 18 inches.
The character displays in a monitor is often limited by the size is 80 characters and totally 20 row in will be displayed at time in the screen.
Printers:
Printers can be broadly be subdivided into two categories;
Impact printers
Non-impact printers
Impact Printers:
Impact printers can be described as printers which utilizes some from of striking device to transfer ink from an inked ribbon onto the paper being printed to form images or characters. Some of other printer falls into this category are,
Dot Matrix
Chain printer
Drum Printer
Daisy Wheel Printer
Non-Impact printers:
Main concept of non-impact printer is no direct contact between printer head and the paper. But in the Impact printer case, direct contact between printer head and the paper. Some of the important non-impact printers available in market are,
Laser Printer
Ink Jet Printer
Thermal Printer
Electro Static Printer
Non-Impact printers are comparatively high cost and the quality of output is also high. Speeds of these printers are high.
Plotters:
Plotters are used to produce output containing graphics or diagrams. With the availability of multi-colour plotters, they are increasingly used for preparing financial documents, annual reports and engineering drawings. Three types of plotters are available. They are,
Drum plotters
Flat bed plotters
Injection plotters
In the drum plotter, both paper and pen move, i.e. Paper move up and down in the rollers, the pen move left and right in the bar so that, the graphics picture is created.
In the flat bed Plotter, paper is fixed in the drawing pad, the pen is fixed in the bar just up to the drawing pad. To create drawing in the paper, pen bar move left to right, and pen move up and down in the bar on the paper.
In the Injection Plotter, ink nozzle sprays the ink with different colors and is able to produce large drawings containing many colors. Quality of the drawing from the Injection plotters in high as its price.
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