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Friday, May 6, 2011

Classification of computer

Different types of computer:-
A wide variety of computers are available in the market today. Computer differ from another according to the speed of their processors (also called chips), intel, a software company, was the first to introduce high speed processors like PII, PIII, PIV, etc. these chips are well-known available in the market are the intel Celeron, AMD Athlon, AMD Duron, Cyrix ,VIA, etc.
The computer could be divided in to number of different categories.

Types of computer

                                                                       
Commonly used computer

Handheld
computers

Advance computers
personal
Mini
Micro
Mainframe
Super
Self Destructing

Laptop
palmtop
Tablet



   


(A.)Commonly used computers:-

1.   personal computer :-  
2.   Mini computer: -
The mini computers originated in 1960s .initial minicomputers were 8 bit and 12 bit machines but by 1970s almost all minicomputers were 16 bit machines. The 16 bit minicomputer was more powerful machine, which could be used in a variety of applications and could support business applications along with the scientific applications. The architectural requirements of minicomputers grew and 32 bit minicomputer, which was called supermini, was introduced. Most of the mini and super mini computer are built over around Motorola’s 68000 series chips.


3.   Micro computer: -
A microcomputer’s CPU is a microcomputer. The micro computer originated in late 1970’s. The first microcomputer were built around 8-bit microprocessor chips. A few microprocessor chips are Zilog Z80, MOS 6502, Intel 8080, and MC 6809. The first 16-bit microprocessor of the series in MC 68000 series chips. It is a 16/32 chip and can support up to 16 MB of primary storage. Advancement over the 16/32 chip and can support up to 32 bit. Some of popular 32-bit chips are Intel 80386, AMD MC 68020 chip. Most of the popular microcomputers are developed around Intel ‘chips. With the advancement of display and VLSI technology now a microcomputer is available in very small size. Ex- laptop, notebook. Etc.

(B.)     Advance computers :-

1.     Mainframe computers: -
Mainframe computers are generally 32-bit machines. These are suited to big organizations, to manage high volume applications. Few of popular mainframe series are MESHA, sperry, DEC, IBM, HP, HCL, etc. mainframe are also used as central host computers in distributed systems, libraries of application programs developed for mainframe computers.

2.      Super computer: -
The super computers are fastest machines in terms of processing speed and use multiprocessing techniques where a number of processors are used to solve a problem. Example of super computers manufacturers – CRAY (CRAY YMP, CRAY 2) ETA (CDC_ETA10, ETA 20) AND IBM 3090 (with vector).
      Super computers have been in use in combination with the mainframe
      Super computers. The super computers are reaching up to speeds well
      Over 25000 million arithmetic operations per second. Super computers 
      Are mainly being used for weather forecasting, computational fluid,
      Dynamics, remote sensing, and image processing, Bio-medical applications.
      
3.    Self destructing computers: -
A device is being developed and the name of the company who first introduce is cyber Group Network corp. (CGN) the name of the device is C4 chip. According to the manufactures of the device a computer embedded with c-4 chip can guarantee 99.9 percent that all information stored on your hard drive is secure. The manufactures intended to expand the device’s capabilities so that it can be used with personal digital assistants (PDA s) and other electronic devices.

Components of the pc:-
The essential and the optional components of a computer are listed in the following table.

Basic components                                                Optional
                                                                                    
  •     Processor                                                                              Printer
  •     RAM                                                                                        Scanner
  •     Display / Video card                                                           Modem
  •     Keyboard                                                                              Speakers
  •     Drives: hard disk, Floppy disk, CD-ROM                      Zip drive
  •     Mouse
  •     Monitor
1.  The system unit (Cabinet):-
The system unit ( cabinet) or chassis is the most important part of outside of the pc. It controls and executes all the operations performed by the pc. Case that contains electronic components of computer used to processed data. It called also chassis or cabinet. The keyboard, Monitor, Mouse, printer, etc. are connected from  to the system unit through cables which are plugged into the back of the system unit. The hard disk, the floppy Disk Drive, and the CD-ROM Drive, Power supply are placed inside the cabinet according their proper ways.

  What are the common components inside the system unit?
1.     What is Motherboard?
  The motherboard is flat platform of fiber glass on which the electronic components in a pc are mounted. Thin lines of metal connecting pins are etched on the surface of the fiber glass. These pins connect the components to one another, and form the electronic circuit of the computer. The motherboard is also called a printer circuit Board (PCB) or circuit board .it contains adapter cards, processor chips, memory chips and all essential parts which is used for processing of computer system.

2.    Central processing unit (CPU) or processor:-
 The central processing unit (CPU) or Processor  is the most important components of a computer.It contains the microprocessor chip which undertakes all the thinking for the pc and runs the program (series of instructions) according to the user’s commands and request. CPU actual processing the mathematical and logical processing, takes place. It is the brain behind all PC operations. Technically, the CPU is also referred to as the microprocessor or Brain of computer.



The speed of the CPU:- 
The speed of the CPU is measured in Hertz. (HZ). A computer has a central clock that keeps all its components it tunes with one another. Hertz named unit is to used to measure for computer processor speed.
 For example : - if any processor takes one seconds (1&) for executing any direction then speed of processor termed as one hertz (1 HZ).
If processor executes 1024 directions in 1 second (1’s) then speed of processor followed I kilohertz (1KHZ) and when it executes 10, 48,576 directions in one seconds (1’s) the speed of processor will be 1 (MHZ). After it performs 107, 374, 1824 directions in one seconds after that it speed termed as 1 gigahertz (I GHZ).
Some Processor manufactures companies are as listed:-                                               
  Intel Pentium IV (1.7 GHZ), AMD Athlon, AMD Duron (600MHZ-1.2 GHZ) , VIA , Cyrix etc.

Main parts of CPU are :-

·          control Unit

·          Arithmetic Logic unit (ALU)

·          Register

1.   What is a control unit?
     The function of a control unit is to make sure the ALU, memory, unit, and input/output   
     Devices are used in logic order and to control the entire operations of the computer. It  
     Controls all the other devices which are connected to the CPU like memory input and output
     Devices. This unit also controls and directs the various units of computer such as it tells the storage unit where to store and allocates to various programs. It is similar to human brain.
 Control unit repeats 4 basic operations:-
·         Fetch: -    obtain program instruction or data item from memory.
·         Decode: - translate instruction into commands.
·         Execute:- carry out command
·         Store: -    write result to memory.

  1. What is an Arithmetic Logical Unit (ALU)?
        The arithmetic logical unit carries out arithmetic operations (Addition, Substraction,
        Multiplication, division), comparison operations (greater than, equal to, less than)
        Logical operations (AND, OR, NOT) and Performs arithmetic (+,-,*, /) and logical (if hours
        > 40) operations.
      
  1. What is a Register?
All the arithmetic and logical operations are performed in the CPU in special storage areas called “Register”.  It holds temporary high-speed storage is holds data and instructions. it consists a number of registers, and each performing a specific functions.

      • Accumulator
        • Serves the purpose of holding data used in calculations
      • Address register
        • Are used for storing the memory location of data and instructions, to be used by a program
      • Stack pointers
        • This register is used during the sub-routine nesting and stack based arithmetic
      • Status register
        • This register provides a service to the CPU by maintaining the status of the last operation carried out by the ALU
      • Instruction pointer
        • This register is responsible for retaining the memory address of the next instruction to be execute


The Memory of a computer:-
Memory is an essential component of a digital computer system. It is a storage area where data, instruction, software, operatring system, program, result, etc. stores in binary form. Ii consists of one or more chips on motherboard or other circuit board computer uses a number of memory devices of different technologies such as semiconductor memory, magnetic memory, and optical memory.
1.  Semiconductor memory: -
The CPU consists of semiconductor device and it operates at very high speed. CPU is very fast semiconductor memory called also cache memory is directly connected to CPU. It stores currently needed instructions and data of a program being executed. It access time is about 10 ns(nano seconds).

 Three types of cache memory

  •   L1 cache -  memory built into processor

  •   L2 cache -  memory has slower but has larger capacity. it has

  • Advanced transfer Cache is faster built directly on processor chip.

  L3 cache is separate from processor chip on motherboard (L3 cache Memory is only on that   computer who uses L2 advanced transfer Cache.

    The next level of memory which is used in a computer system is the main or primary memory.
It is also fast semi conductor memory. It stores programs and data which are being processed by the CPU. It access time is about 50 ns. It is cheaper than cache memory.   
Types of semiconductor memory:-
       There are main two types of semiconductor memory.
  • RAM (Random Access memory)
  • ROM (read only Memory)
  1. RAM (Random Access Memory):-
Random access memory (RAM) any memory location can be accessed in a random way without going through any other location. RAM is used as read/write memory of a computer. RAM is volatile memory .it stores information as long as power is supplied to it. It contents are lost when power supply is switched off it interrupted. The use has to reload his program and data when power supply is resumed. Ram chips that can be read and write by processor also called main memory or primary storage. When the computer starts os files are loaded from HDD in to RAM. Packaged on circuit bard called SIMM and DIMM.
There are two types of RAM:-
(A.)  Dynamic RAM (DRAM):-
DRAM loses its stored information in a few milliseconds even though its power supply is on. Dram consumes less power. It is cheaper than static RAM.DRAM memory chips are placed on SIMM (single In-Line Memory Module). The capacity of 4M*36 SIMM is 16 M bytes (MB).


    Types of Dynamic RAM

·         SD RAM                  (Synchronous Dynamic RAM )
·         RD RAM                  (Rambus Dynamic RAM)
·         DDRSDRAM            (Double Data rate )
·         VRAM                       (Video RAM)
·         SG RAM                   (Synchronous Graphics RAM)
·         EDO RAM                 (Extended Data output RAM )


(B.)  Static RAM (SRAM):-
A static RAM retains the stored information as long as power supply is on. It is faster and reliable than DRAM chips less volatile and more expensive the DRAM chips used for special application such as Cache.    

  1. ROM (Read Only Memory):-
 ROM is Non-volatile memory. It stores information permanently. Its contents are not lost when its power supply is switched off. ROM is used to store permanent programs. It is used to store initializing programs of a computer component, Monitorkit chips etc. it ia also called Non- Volatile Memory (it means does not loses it contents when computer power is turned-off. 
Ex- BIOS of motherboard.

Three types of ROM:-
1.      PROM( programmable ROM) :- blank ROM chips on which a programmer can write
A program, data or any other kind of information only once.
      2.   EEPROM (Electrically erasable PROM):- EEPROM is byte erasable. Its contents
            Can be erased and programmed on the system board itself very easily on byte to byte
            basis. Ex- flash memory,
2.       Firmware: - ROM chips manufactured with permanently written data, instructions or information

       Flash Memory: -
      Non-Volatile memory that can be erased electrically and Reprogrammed. It is used with PDA,
      Digital cameras Digital Cellular Phones, Music players, Digital Voice, recorders
      
3.      CMOS :- 
it stands for Complementary metal-oxide semi-conductor (CMOS) used in
       Some ROM chips, .it retains information when the power is switch- off as battery
       Power.
    Example- Disk-drives, key-board, Monitor, Current date & time of Mother Board.


  Magnetic memory:-
  The magnetic memory is permanent memory. It is not volatile memory. Following types of magnetic memory are used in computer system.
       Hard disk: -
Hard disks are on-line storage device. They are used as secondary memory for mass storage of information permanently; they store programs, data, operating system, and compilers, application programs, database, and etc.
Capacity and Performance:-
A typical desktop machine will have a hard disk with a capacity of between 10 and 400 GIGABYTES (G.B) or more capacity as Terabyte (TB) in present days.  Data is stored onto the disk in the form of files. A file is simply a named collection of bytes the bytes might be the ASCII Codes for the characters of a text file. It is a sealed or coated round shape aluminum box with controller electronics circuit board equipped with essential electronics components attached to one side. The electronics control the read/write mechanism and the motor that spins the platters. The electronics also assemble the magnetic domains on the drive into bytes (reading) and turn bytes into magnetic domains (writing). The electronics are all contained on a small board that detaches from the rest of the drive


Inside parts of Hard disk: -
The platters –
Platters are mainly parts inside of Hard disk typically spin or rotate at 3,600 or 7,200 RPM (Rotate per Minute) when the Hard drive is operating.


Arm
Arm holds the read/write heads and is controlled by the mechanism in the upper-left corner. The arm is able to move the heads from the hub to the edge of the drive. The arm and its movement mechanism are extremely light and fast.



Storage Data:-
Data is stored on the surface of a platter in sectors and tracks. Tracks are divided in concentric circles, and sectors are pie-shaped wedges on a track, like this:
A sector contains a fixed number of bytes -- for example, 256 or 512. Either at the drive or the operating system (OS) level, sectors is often grouped together into clusters.
Working process of Hard Disk Drives (HDD) :-
Hard Disk consists of a stack of multiple metal platters coated with iron oxide and joined spindle. The hard disk , a set of Read/Write heads and a Motor to rotate the disks , are sealed in a vacuum chamber to protect it from the dust and out side environmental effects.
The rigidity of the hard disk , the multile platters used and high speed of revolution allows lots of data to be stored on the disk and fast access to the data is made possible. It is stack of platters, the term cylinder refers to the same track acrtoss all the disks. Outer most track is 0 , so the outer most cylinder is also 0(Zero).
Floppy Disk Drives (FDD) :- 
Floppy disk is new kind of storage device that was developed as form of chipper and fster storage devices as like small random access disk. Floppy disk drive (FDD) reads and writes data to a small, circular piece of metal-coated plastic similar to audio cassette tape. article,
History of the Floppy Disk Drive (FDD):-
The floppy disk drive (FDD) was invented at IBM by Alan Shugart in 1967. The first floppy drives used an 8-inch
disk (later called a "diskette”) which evolved into the shape of 5.25-inch disk that was used on the first IBM Personal Computer in August 1981. The 5.25-inch disk held 360 kilobytes compared to the 1.44 megabyte capacity of today's 3.5-inch diskette.
The 5.25-inch disks were dubbed "floppy" because the diskette packaging was a very flexible plastic envelope.
Parts of a Floppy Disk Drive :-
Floppy disk are made of myler (plastic material) coated with magnetic material (iron oxide). This disk is not like as hard plate rather than thin plastic flexible coated device. The surface of disk is made of tracks. These tracks are arranged in several circle o the surface of a disk. Data are stored in the form of magnetic spots on its tracks. Tracks are divided in to sectors. In each sector in a track is known as an address. Different size of floppy disk are 5.25 “and 3.5 “diameter available in markets. A floppy rotates at 360 R/M/ its average access time is 102 to 250 m/s.
Two types of standard size in floppy disk as follow:-
1.    Mini floppy –      5.25”        capacity –    360K.B to 1.2 M.B.

2.    Micro Floppy – 3.5 “          Capacity –    1.44 M.B.
What is Mini Floppy :-
Two types of mini floppy as follow
1.    Double size (Double Density (DS/DD)
2.    Double Sided ( High Density (DS/HD)



Optical storage Disks:-
The optical storage device most of familiar with as compact disc (CD) to capable of holding up to 600MB to 750  MB  data storage and more as 4.7 G.B in DVD Disk. This technology has been developed by Sony and Philips in 1970.
In CD, there is thick layer of poly carbonate plastic base. On the top of CD Base layers of organic dye, a thin layer of gold of to reflect layer beam a protective layer and finally a layer of scratch resistance polymer materials.
Data is recorded as tiny pits on a polished surface denoting “1” which are ready by reflection produced when laser beams are focused on them for reading the laser beam employed 5 MV (Microvolt) and writing employed as 25 MV. The reflected laser is sensed by photodiode to read data. 
In CD read and write data with the help of laser beam which is direction with the help of lenses, prism and mirrors. Data is stored by the laser beam in the form of lands and pits. Land is the metal surface which reflects the light (interrrpretal as 1) into the sensor and the pit is the hollow surface which scatters the light(interrepted as 0) while data is being read from the disk.
Speed of CD Drive known as X ( 52X printed on CD drive)  and 14 X on the DVD Drive that measures the rate of data transfer from the CD to computer.

Within a CPU, instructions are written in the form of computer programs which are carried by the CPU sequentially. The processing capability of a PC is measured in term of the amount of data processed by its CPU in one operation.

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