- Central Processing Unit
- Input Devices/media
- Output Devices/media
Some special purpose devices and media are also available.
CPU (Central Processing Unit)
The CPU is also called the brain of the computer. Its basic function is to perform calculations and various logical operations. It consists of three parts: -
1. Control Unit
- It consists of electronic circuits
- It selects, interprets and executes instructions.
-Governs input/output (I/O) operations, data transfer to and from storage and guides the routing of data between storage location and the arithmetic and logic unit.
2. Arithmetic and Logic Unit (ALU)
- Comprises of electronic circuits.
- Performs calculations and comparisons.
- Works at tremendous speed and executes millions of instructions per second (MIPS).
3. Memory or Storage
- Also called Internal storage or main memory or random access memory (RAM).
- Consists of very fast memories like magnetic core memory or semiconductor memory.
- Stores program instructions or part of data for immediate need.
- Data is stored in a computer memory in the form of words, bytes and bits.
Keyboard
Keyboard is an input device. Computer keyboard is an electromechanical component designed to create special standardized electronic codes when a key is pressed.
Keyboards come in a variety of sizes and shapes having a number of features in common:
1. Standard TypeWriter keys 2. Function keys 3. Special purpose keys 4. Cursor Movement keys 5. Numeric keys
Mouse
The mouse is also an input device that is much in use nowadays in graphics as well as when working with a GUI(Graphic User Interface).
About the size of an audiocassette, it slides on a rubber ball and has two or more buttons on the top. When a mouse is slid across a flat surface, the screen cursor also moves in the direction of the movement of the mouse. With a click of the button, the system can be notified of the selected position.
VDU
Visual Display Unit is the most popular I/O device used nowadays for interactive processing. A keyboard is used to enter data into a processor and a Video Display Unit, called Monitor, is used to display the keyed data and to receive processed information and messages from the computer.
Visual Display Unit/Terminal
VDTs are classified as:
1.Dumb terminals:
These are simple devices that immediately transmit each keyed data character to the processor.
2.Intelligent terminals:
These combine VDT hardware with built-in microprocessors. They can process small jobs without the need to interact with the main computer
MICR
Magnetic ink character recognition devices were developed to assist the banking industry. It is used in the processing of cheques.
The most commonly used character set by MICR devices is known as E13B font that consists of numerals 0-9, and 4 special characters.
Scanners
These are basically input devices that are capable of recognizing marks or characters. They are used for direct entry of data into the computer.
Different types of scanners are:
1. OCR
These are scanner devices that are capable of detecting alphabetic and numeric characters by comparing the shapes with internally stored patterns. These are expensive and are used only for large-volume processing applications e.g. by credit-card companies
2. OMR
These scanners are capable of recognising a pre-specified type of mark made by a pencil. These are normally used for validation of input documents, evaluating answer-sheets in objective-type tests e.g. GRE, GMAT.
3. Bar Code Reader
Data coded in the form of light and dark lines or bars are known as bar codes. Bar codes are used particularly by the retail trade for labeling goods. Bar code reader is a device used for reading bar code data which is performed by laser beam scanner which is linked to a computer.
4. Desk Scanning
The scanning process involves application of the light source to the image. The light is reflected back form the image into the scanner optics where the varying levels of light are interpreted.The image is then reconstructed digitally and displayed on the screen.
Touch Screen
It is a computer screen designed or modified to recognize the location of a touch on its surface. By touching the screen, the user can make a selection or move a cursor. The simplest type of touch screen is made up of a grid of sensing lines, which determine the location of a touch by matching vertical and horizontal contacts.
Light Pen
A light pen is a pointing device. It is used to select a displayed menu option on the CRT. It is a photosensitive pen like device. It is capable of sensing a position on the CRT screen when its tip touches the screen. When its tip is moved over the screen surface, its photocell sensing element detects the light coming from the screen and the corresponding signals are sent to the processor.
Output devices
Printers
Printers are primary output devices used to prepare permanent documents for human use. Printers are classified as:
1. Impact printers
i). Letter Quality Printer
ii). Line Printer
2. Non-Imapct printers
1. Impact Printers
These operate like a typewriter, pressing a typeface against paper and inked ribbon. e.g. daisy-wheel printer , dot-matrix printer.
i). Letter Quality Printer:
These are also called character printers or serial printers because they print one character at a time. They produce a very high quality print image (one that is very clear and precise) because the entire character is formed with a single impact such as a Daisy Wheel Printer or a Dot Matrix Printer.
a) DMP (Dot Matrix Printer): These are serial printers, i.e., they print one character at a time. Each character is printed as a pattern of dots.
b) Daisy Wheel Printer: These printers have a print wheel with a set of print characters on the outside tips of flat spokes. You can print a specific character through spinning the wheel.
ii). Line printers
These are very high speed printers, which cater to huge volumes of output requirements of large computer organisations. These are known as Line printers because they use impact methods to produce one line at-a-time printed output. e.g. chain printer, band printer, drum printer.
The ink jet printer ejects a steady stream of ink drop towards the printed page. The drops are selectively discarded by electrostatic attraction to leave only those that are needed to form the desired symbol. Those that are not needed are captured in a tiny gutter & filtered to remove impurities. They are then recirculated through the drop-generating mechanism.
iii). Laser Printer
This printer is much less mechanical than impact printer (that is, no print heads move, no print hammers hit). resulting in much higher speeds and quieter operation. The process resembles the operation of a photocopy machine.
The major advantages of laser printers are:
1. Very high speed.
2. Low noise level.
3. Low maintenance requirements.
4. Very high image quality.
5. Excellent graphics capabilities.
1. Memory Location
- Memory of the computer is divided into small parts called locations.
- Each location has a unique address.
- Location is further subdivided into bits.
- Different computers have a different location size varying from 8 to 64 bits.
2. Bit:- Bit stands for one binary digit, which is either 0 or 1.
3. Byte:- Number of consecutive bits combine to make a byte.
Most commonly used combination is of 8 bits. Size of main memory is given in Kilobytes (KB) or Megabytes (MB).
08 Bit = 01 Byte
1024 Bytes = 01 Kilobyte (KB)
1024 KB = 01 Megabyte (MB)
1024 MB = 01 Gigabyte(GB)
Primary Storage / Internal Memory / Main Memory
The main memory, also called random access memory (RAM) is the work area of the computer. It stores program instructions or part of data for immediate needs.The storage capacity of RAM is limited. A typical modern computer can have a RAM size of 32MB or 64MB or greater upto 8GB. It is volatile memory of the computer and when the power goes, the contents stored in RAM are lost.
RAM can be classified as DRAM(Dynamic RAM)or SRAM(Static RAM).
Secondary Storage
The secondary storage devices are used to store programs and data on a permanent basis. Their storage capacity is much higher compared to main memory of the computer. Secondary Storge devices accept data or program instructions from the processor, retain them and then write them back to the processor as and when needed.
The examples of secondary storage devices are Floppy disk, Hard Disk, Magnetic tapes, Pendrives or jumpdrives etc.
Floppy Diskette
The floppy diskette is a direct access storage device although its capacity is much less than a hard disk. The diskette is made out of a flexible plastic material. This base is coated with an iron-oxide recording material. Data is recorded as tiny magnetic spots. The surface is divided into tracks and sectors, same as in a hard disk. The number of tracks on a diskette depends on the recording density. The size of each sector is fixed (512 bytes). Data is stored on both sides of the diskette. There is one head per surface in the floppy drive for reading/writing data on the diskette. The circular plastic disk is enclosed within a smoothly lined, protective square jacket to protect it from dust and scratches.
The standard size available nowadays is: 3.5 inch.
These are specific kind of storage devices that can not be removed and are fixed inside the computer. That is why these are also called as fixed disks and store programs permanently.The storgae capacity of the disks that are used these days are having Gigabytes of storage and these are faster in comparison to Floppy disks.
Magnetic Tape
This is also a magnetic media which stores data sequentially in them . Though they provide unlimited storage capacity they suffer form a very serious problem. Since the data stored in them is sequential in nature, retrieval of data takes a very long time. These are used for archival backup storage.
CD-ROM
Compact disk, read-only memory optical disks have a very large storage density and the access time is relatively low.
Digital Versatile Disc
Digital Versatile Disk is in genre of optical discs with same overall dimension of CDs but much higher capacity. These can store at least 7 times more data than CD ROM.
Static Memory and Memory Sticks
Also commonly known as pen drive or jump drive or flash drive. Static memory devices use memory chips to store information. This information is retained even after power is turned off. They connect to a USB port on the computer and offer capacities of 128 MB or more. Due to their size and shape, these devices are known as USB memory keys or flash drives and have widely replaced floppy disks for transportation of files between systems. Many portable and hand-held devices rely entirely on static memory for storage.
Semiconductor Memory
These days, internal memory consists of extremely small bit storage circuits (flip-flops) etched on a silicon chip. All the electronic elements to store a bit are placed in such a small area of the chip that a single chip can store millions of bits. The individual chips are arranged in groups to form a memory module.
Types of Semiconductor Memory
i). Random Access Memory (RAM): Any information can be read from and written into a RAM. It is a read/write memory. It is a volatile memory i.e. its contents are lost if the power supply is interrupted or turned off. The main memory of the computer is RAM.
ii).Read Only Memory (ROM): ROM is permanently programmed with information during manufacture, by implementing the appropriate pattern of two state values. It cannot be changed subsequently by a normal write operation. It is thus completely non-volatile. It is mainly used to hold those programs, which are required permanently.
iii). Programmable Read Only Memory (PROM) : This can be programmed to record information using a special electronic equipment known as a PROM programmer. However, it cannot be changed subsequently.
iv). Erasable Programmable Read Only Memory (EPROM): EPROM is a PROM, which can be reversed by exposing it to an ultraviolet light source. The device can be re-erased and re-programmed again and again.
v). Cache Memory: It is a small capacity high-speed memory used to make processing faster. The main memory can process information very fast, but it takes much longer to transfer data to and from the input/output devices. The cache memory compensates for this mismatch in operating speeds. It holds those parts of data and the active program, which are most frequently used. Thus, the performance rate of the CPU improves.
0 comments:
Post a Comment