5)On the basis of brand
On the basis of brand computer can be classified as:

i) IBM
The computer that are manufactured by IBM are known as IBM PC.IBM PC is one of the leading company of the world in manufacyuring computers.These are more reliable ,durable & have better quality.It was also very expensive in comparision to IBM compatible computer.It was specifically designed for professional & scientific problem solves.

ii) IBM Compatible
The computers that are manufactured by other companies but having same technology & fetures of IBM PC are known as IBM Compatible.such computers are refer to as Pc clones or IBM clones.Since they almost exactly duplicated all significant features of PC architecture facilated by various manufactures.

iii)Apple Mac
the computers that are manufactured by Apple Mac company but having different architecture & configuration then IBM compatibles are known as Apple Mac.They have system produced by Apple company for their maintosh is called Mac OS.




) 6) On the basis of model

i) XT(Extra Technology)
The computers having 8000 ,8086 ,8088 microprocessor & processing speed of 4.TT mega hertz are known as XT.It can’t support GUI (Graphics User Interfare) based operating system.

ii) AT
The computer having 80286 ,80386 ,80486 ,Pentium-I Pentium-II & Pentium-IV microprocessor & processing speed.

iii) PC 12
It is a laptop computer with rechargeable battery based system.It is operated with OC1R operating system.These computers are use refinal architecture making the computer faster than AT computer.They can almost all programe.eg:laptop hand held computer.

Number system.

1. Decimal (0-9)10
2. Binary (0-1)2
3. Octal (0-7)8
4. Hex (0- )

Today we can’t imagine a world without numbers.It took thousands of years to get the decimal number system.In the stone age man used pebbles sticks & different types of symbols for counting numbers.all the techniques requires some physical power from man.The process was very slow & a lot of works was required for large calculation.Later on above techniques were replaced by the present day number system.Besides decimal number system there are other system namely binary ,octel & hex.

1 ) Decimal number system
The number system having base10 is called decimal number system.it includes 10 digits.Since there are 10 digits in decimal number system it’s base is 10.The order of base values in decimal number system are 1 ,10 ,100 ,1000 e.t.c.

2) Binary number system
The number system having base 2 is called binary number system.It includes only two digits 0 & 1.Since there are omly two digits it’s base value is two.The order of two values in binary number system are 1 ,2 ,4 ,8 ,16 ,32 ,84 ,128 , & so on.
1 or 0 is also called bit ,which represents two logic conditions:
1.True &
2.False

1) Octal number system
The number system having bsae 8 is called octal number system.it includes 8 digits i.e. 0-7.Since there are 8 digits in octal number system it’s base is 8.

5)Hexa decimal number system
The number systemj having base 16 is called hexa decimal number system.It includes 16 digits.eg: (0-9 A ,B ,C ,D ,E ,F).Since there are 16 digits it’s base is 16.

Fourth generation of computer
The fourth generation of computer were developed during 1974-till.They used micro chips having about -50,000 transistors on a chip as a major component.
A micro chip is a single chip that consists of the entire computer circuiting American intel corporation develop the first microprocessor called 4004 in 1971.The main features of this generation of computer are:
-Highly reduce the size of computer.
-The operating speed increase beyond HIPS(million Instruction Per second)
-Magnetic & optical storage devices with capacity more than 360 GB.
-Mltiprocessing & multiprogramming operating system are used.
-4G(Fourth generation) languages are used eg:Ctt,Java,Net e.t.c.
-Eg:8086,8088,80286,80386,80486,80586,(Pentium-I,II,III,IV) e.t.c.

Fifth generation of computer
The development of fifth generation of computer is being started but not completed til now.These computer will use Bio chips which are made from Gallium & Arsenite as major component.Japan has been working to develop such computer using the concept of A.I.
(Artificial Intelligence)
Features of fifth generation of computer
-Able to understand human language & speak ,think & make decision.
-Can perform large number of parallel processing.
-Speed is extremely high.


Classification of computer
1) On the basis of work.
a. Analog computer
It work on the supply of continious electrical pulse.The display of output is also continious.It has a very limited memory.It can perform a limited type of calculation.It is used for only scientific research & engineering purpose.eg:automobile ,speedometer ,clock with a two hand & slide rule.

b. Digital computer
It dosen’t work on the supply of continious electrical pulses.It has a very big memory.Generally ,we use digital computer in our daily lifea.It is used not only for scientific research & engeneering purpose but also in industries ,government sector ,education ,medicine ,law ,social services e.t.c. a digital computer is one that directly counts numbers or digits that presents numbers ,letters or other special symbols.eg:digital clock ,present computer.


c. Hybrid computer
The computer that processes the features of both analog as well as digital is called hybrid computer.These are used on intensive care unit of hospitals ,jet planes & other data analysis terminals.It is very useful & confidend in scientific research ,medicine & engineering purposes.


#Difference between Analog & Digital computer
1) Analog computer
#It is costly.
#It is used in scientficial ,medical & industrial field.
#It is specific slow & less accurate.

2) Digital computer
# It is less costly.
# It is used for statical data numerical problem &
Science
#It is versatile ,fast & accurate.


1) On the basis of size
a. Super
It is the largest computer of very high efficiency & storing capacity having feature of multi user of multi processer.It be able to solve very difficult & complex problems within a nanosecond.It use RISC processor.(Reduced Instructor Set Computer)
It is used in the following:
1) Used in forecasting weather & climate.
2) Used in millitary research & defense system.
3) Used in encrypting decoding sensitive intelligence information.
4) Used in automobile aircraft & spacecraftdesigning.
5) Used in seismography plasma & nuclear research.
6) Study of DNA structure & gene engeneering.
7) Digital film rendering.
8) In metrology
Eg:PAEAM ,services developed by C-DAC ANURAG ,CRAY-I ,CYBER 205 e.t.c.


b. Mainframe computer
It is very powerful muti-user ,general purpose computer system & supports wide range of input & ontput terminals with large backing storage capacity.It supports large number of terminals upto 100 or more.It works on the hime saving basis.the first mainframe compater dereloped by ibm was system 360.

Applications:
-Credit card procession.
-Bank account management.
-Business data processing.
-Air traffie coutem & induslrial design.
Eg:system1360 ,IBM 51390 ,IBM 51709 e.t.c.

3) Mini computer
Mini computer is also known as mid-range comouters & more powerful & larger than micro computer.It is also multiuse computer & supports more then dozens of people at a time.
Applications:
-Used in universities.
-Used in large business.
-Used in scientific research instrumentation
System ,industial process.
-Used in monitering & controlling system eg PDP-II (Program Data Processor)

2) Micro computer
It is also called home PC or desktop PC because it is a single user computer.it supports many high level languages ,multimedia graphics ,3D-graphics & games.It is popular among students ,professionals due to small size ,low price & low maintainance cost.

Application:
- For different programming ,graphic designing &
desktop publishing.
- For listening multimedia songs e.t.c.

Types of micro computer
i)Laptop
ii)Palmtop
Types of micro computer
i) Laptop
ii) Palmtop
iii) Multimedia
iv) PDA (Personal Digital Assistant)



i) Laptop/Palmtop
These are small ,portable ,less power consuming & equipped with all the facilities of modern PC.These computers can be operated by battery.These computers have as equal as storing capacity like desktop & all facilities are included.It has CD-Drive ,FLOPPY DRIVE ,COMBO & other input output parts.

The idea of laptop computers was started by Alien kay of Xerox palo alto research centre in 1970 & named to notebook but the first laptop was designed by William Moggrage of grid system in 1979.Palmtop computers are very useful for remote areas where there is no electricity. Facility available.
The higher authorities ,social working in remote areas.They get more benefit by palmtop as well as laptop.
Simply the desktop is your personal computer seated at the top of your disk laptop as no problem on your lap & palmtop on your palm.


ii)Multimedia computer
Multimedia is a combined form of two or more media like as text ,graphic ,sound & animation e.t.c. ADC (Analog Digital Computer) converts he sound wave into digital signal in multimedia computer MPEG (Motion Picture Expert Group) is a standered use to compress sound (audio) & videos for computer name HPEG-1 ,MPEG-2 e.t.c.


iii) PDA
PDA is a small sized portable hand-held electronic edvice which has all the features of PCs.It has input processing storage & output capability like the other micro computer.We can transfer data from PDA to PC & PC to PDA.It is used for daires calendar ,address ,book e.t.c.

(3)UAIUA
It stands for Universal Automatic Computer developed by J.P eckret & DR. John Mouchly in 1961.It was capable of processing alpha numeric data & based on the concept of stored memory of John newman.It was used for business data processing which was the first computer manufactured for commercial use & general purpose digital computer.

(4)EDSA
It stands for Electronic Delay Storage Automatic Computer.altough the concept of store programme was introduced EDVAC,EDSAC was the first computer implementing this concept.It was designed by Mauric Willes in 1947.It is used as Mercury delay line storage system where the exess time was 1 mini second.It contains 3,000 vacum tubes & operated on 30 kilo watt.

History of computer in Nepal:
-First ‘Facit’ named calculating device was brought in
2018 B.S. for census purpose.


-In 2028B.S. “IBM 1401” was the first computer computer brought in Nepal which was the second generation of computer.

-During 2039 B.S. different types of computer like ‘Sirus’ ,‘Apple Mac’ e.t.c. was brought.

-Till now we are using laptops,palmtops e.t.c. & the technology is still using.

#Generation of computer

(1)Rise in step of technology
The step of technology in computer system is termed as generation of computer.Simply the generation of computer Each generation is distinguish from others on the basis of the type of switching circuits.
There are five generation of computer:

Generation Duration Components
First 1943-1958 Vacum tubes
Second 1959-1965 Tansistors
Third 1966-1973 IC-chips
Fourth 1974-Till Mcro -chips
Fifth Future Bio chips




First generation of computer
The first generation of computer were developed in 1943-1958 A.D.They use the vacuum tubes as the switching device.Lee De forest first developed vacuum tubes.

#Features of first generation of computer.
1)Very long in sieze,very slow.
2)Consume high power & produce large amount of heat.
3)They have slow speed,operating & limited computing & storage capacity (1-4B)1024+1024 Byte.
4)Programming was done in machine level language.
5)Programming was difficult & expensive eg:ENIAC,EDVAC,UNIAL,IBM650IBM701 e.t.c.


Second generation of computer
The second generation of computer was developed during 1959-1965 A.D.Tey use they use the transistors as the main switching device.John Barden &Willium B.shockley developed.

Features if seeond generation of computer
-They were smaller than first generation of computer
-They consumed less power & produced less heat in comparism to first generation of computer.
-They are faster & more reliable in processing.
-Less costly & capable of storing largeamount of data.
-Programming would be done in high level language like ‘CBOL’(Common Business Oriented Language)
-the operating speed was in terms of microsecond. eg:IBM 1401,IBM1620,CDC3600,CDC1804 e.t.c.

Third generation of computer
The third generation of computer was generated/developed during 1966-1973.They used IC Chips as the major components.Jack Clair Kilby developed it.
An Ic Chip is a circuit with number of transistors integrated on a small silicon chip.The main features of this generation of computer are as follows:
-They are small efficient & reliable.
-Operating speed was in terms of nano second.
- Semi-conductor memory was used as primary memory, magnetic disk was used as secondary memory.
-Understanding large numbers of high level languages eg:FORTAN(Formula Translation Pascal )e.t.c.-Input & output devices such as keyboard & moniters were used Eg: IBM 360,IBM 370,ICL 1900,VAX 750PDP-II

History of computer

History of computer means the gradual change in the concept of time around fifth centuary,hindu philodopher developed a new method of counting from 1 to 9.After me the scientist Alkharism developed 0.In this way decimal system envolved.
the development of cunting started from the development of simple counting device called abacus.An abacus is the first manual calculating device.It consists of rectangular wooden frame with movable beats threaded with a spring or rods.It is d into two parts by a middle bar called 'heaven'& the part below the middle part is called 'earth'.There are five beats in each string of earth & two beats in each strings of heaven.In beat in the earth stands for one(1) & each beat on heaven stands for valfive(5).
#Nepiers bone
john napiers developed a method logarithm in 1614 AD to simpliphy the multiplication for that he invented a calculating device known as nepiers bone.
It was a set of number rods that could be used to multiply,divide&extract the rootsThe rods were called nepiers bone because they were made of bones.

#Willium Oughtred
He developed a manual calculating device called slide rulein 1620 A.Dit was based on logarithm.it is easy to find the product of quotient & any other function by alining two scales properly.

#Blaise pascal
Blaise pascal invented a calculating machine called pascaline or the adding machine in 1642.Pascal built the machine when he was only 17 years old.He developed that device to help hi father in his work.This machine could only add & subtract but it couldn’t multiply & divide.
the #Leibrity-Stepped Recknor
Gottfried Williem van Leibrity invented the first calculator called Step Recknor in 1671 which employed the stepped gear principalyhe calculator could not only add & subtract but it could also multiply & divide.

#Charles Babbage.
In the history of computer there have been very important achievement in the early 19 century.
Charles Babbage developed the idea of computing machines which could perform the calculation as well as could make logical decions.he designed the first computing machine called Difference enginein 1822 that could compute upto 20 decimal places.
Babbage further aimed at designing a machine that could accept input,processes & stores them & gives the printed output in the form holes so,he worked on the project to design analytical engine in 1833 to remove limitation of difference engine.
The idea of babbage can be summarized as:
-Memmory can be stored in a machine.
-The concept of B.I.T. was also proposed by him
-Data & programme instructions are fed by punch card.

Now a days all computers are based on it’s idea.So he is known as the father of computer

#Lady Agusta Ada Levelace
Ada corrected some of the errors & improved babbage.She suggested of using decimal number system.She is the first person to develop the programme by using the binary numbers so she is consider to be the first programmer in computer science.

#Dr.Herman Hollerith
Dr. Herman Hollerith who was a staticianon the census on USA in 1800 A.D. At that time,It was very difficult to complete the process of census that would take ten years.So he invented a calculating machine called tabulating machine.So to help in calculating the US census of 1890.
To develop card bases on the idea of Charles Babbage & use the tabulating machinesto reduce them with the help of tabulating machine the whole project .censuswas completed.He formed his own company named tabulating machinecompany in 1896 to commercially his invention.Later he in-corporated the tabulating machine company into IBM in 1924 which is the leading computer manufacture in world even today.



#DR.Howerd aiken
DR.Howard aiken developed an automatic calculating device called Mark first in 1937 but completed in 1944.It was also known as automatic sequence control calculator.
Mark-first computer was very huge in sieze having 51 feet length 8 feet height & 3 feet wide usinjg 1800 vacum tubes.It consists of 7,50,000 parts & weight approximately 32 tones.Cable connection were nearly about 500 miles tones.

#ABC
The Attensoff berry the computer was thewas the electromechamical digital computer built in 1937 by john.v.atansoff &cliffed berry.it introduces the binary arithmetic,regrative memory & logic circuit.this machine lie the foundation for the development of electronic digital computer.
ABC:
Electronic computer (atanasaffy berry computer.)
(1)ENIAC-(Electric Numerical Interegrator & Calculator)
ENIAC stands for electronic numerical integrator & calculator.It was the first large electronic digital computer developed by DR.John presper Eckerd & DR. John Mouchly in 1946.
It was beheld from 1800 vacum tubes &1700 registers.It’s power consuming capacity was 50,00,000 kilowatt.It occupied the space of 1800sq feet used for preferring ballistic weather prediction automic energy calculation of random number study.

(2)EDVAC
It stands for Electronic Discrete Variable Automatic Computer.It was the first computer having the concept of stored programme developed by DR.John Van Newman.the key element to the van newman architecture was the cpu which allowed all computer function to be co-ordinated through a single source.he was regarded as father of store programme .It was completed in 1450.

dvd

CD-ROM

• CD-ROM stands for Compact Disk Read Only Memory.It is made from poly carbonate & covered with high reflective almunium.Diameter is 12 cm & thickness is 1 mm having weight of 16 grams.

• Information is stored in spiral tracks which have pits & langs to store information.It's storing capacity is 700 mb .
  

• Laser beam is used to read data from CD-ROM leaser beam falls on pit & land & reflected to photodiode from the small amount of light is reflected to photodiode from the small amount of light is reflected to photodiode from pit & sufficient light from land the amount of charge in light is converted into electrical signals.
  

DVD
It stands for Digital Versatile Disk.It's storing capacity is 15 times greater than CD-ROM.

The DVD of 4.7 Gb, 8.5 Gb,20Gb,e.t.c. are avialable in the market.It is also called super density disk (SDD).It is avialable in two formals:

a) Video format

b) DVD ROM format

The video format is used for movies & DVD-ROM format is used to store games,photographs & videos.

• Magnetic tape

It is a strong device which is madeup off strong plastic & mylar when data is stored.

The magnetic tape is commonly 732 m long by length & 22m by width.the one side of the tape is coated with magnetic material dot represent 1 & 40,000 character pen inch.The storing capacity is 500 mb,2Gb,4Gb & 10Gb & more.The group Of data stored & arranged in tpe is called records & a group of records is called block.

• Advantage

- durable

- cheap

- high data storage

- suitable for both procesing

- no complicated software is requiredfor file handling

• Disadvantage

- slow data rate transfer

- data can't be arranged in sequential order.

- difficult to recover from parity error.

• Zip disk

It is called super floppy which is inserted into zip drive to store large volume of files,programmes,Incages,videos & back up system.

It can store data equivalent to 70 floppy & storing capacity is 100 MB to 300MB.

• Jaz drive

It is similar to zip drive which can use to store back up & more large office application files,digital music,presentation digital videos to provide back up your os.

Jaz drive come with ultra SCSI card.It has two types namely Internal & External with a jaz drive.We can back up 1 Gb hard disk in as little as 5 minutes.

• Worm
  

It stands for Write Once Read Many.It is optical disk memory.The user can write data on worm & the written data as many times as we want.In worm the written process is normally slower than the reading process.

After writing into WORM disk,It behaves just like a CD-ROM.IT is commonly known as CD-R(Compact Disk Recordable)

# Virtual memory

In computer system there is mainly secondary disk storage memory & main memory.Secondary memory are cheap in price and memory is expensive & has limited storage.So to perform the data processing we have to use some secondary memory as a main memory.Such part of memory is called virtual memory.

• Reason for using virtual memory

-To allow users to have convinence of using large adressable memory space without worrying about physical main memory size limitations.

-In multiprogrammingsystem to allow effecient sharing of memory space among different users economically

• Flash memory

It is an upgrade version of EEPROM.It is trinsistors memory with very fast reprogramming capability.It is suitable for storing control code for BIOS(Basic Input Output System).It's entire contents can quickly be erased but it is erresed & written at byte levels.

It is mainly used in digital cellular phones,Digital camera & so on.

memory

Some terms regarding cache memory.

• Cache hit

If data is avialable at first processor send adress of desired data to cache that eventis called cache hit.

• Cache miss

• The performance of cache is measured in cache ratio.It's value is 0.g & aware.Primary memory

• The fast entegrated memory of less capacity is primary memory.Eg:ROM,RAM,Cache e.t.c. These memories have great effect on processing speed of computers. Main memory

Main memory has registers which is called MAR(Memory Adress Register)to be acessed another register is MBR(Memory Buffer Regster)which also has an input & output part through which the data transfer take place to & from the adressed location.

The main function of main memory is READ,WRITE,& CLEAN.

a) READ

READ signal when applied READ contents of a memory locations specified by the MAR in to MBR.

b) WITE

WRITE signal when applied,causes contents of MBR to be witten in the memory location.

c) CLEAR

CLEAR signals have same function as that of READ signal except the data READ is not looded with MBR.

Difference between.

a)Primary memory & secondary memory

• Primary memory

1) It is a semi conductor memory.

2) In memory hierchy.it is placed in highest position due to high speed.

3) It's storing capacity is small.

4) Processor directly acess it.Eg:ROM,RAM.

• primemory

1) It is a magnetic & optical memory.

2) In memory hierchy It is placed in lowest position due to low cast & large in size.

3) It's storing capacity is large.

4) Processor dosen't directly process it.It is acessed through I/O entrance.Eg:floppy disk, hard-disk,CD-ROM,DVD,Pendrive.

b)RAM & ROM

• RAM

1) It stands for Random Acess Memory.

2) It is also called READ/WRITE voalitile memory.

3) It contents is lost if power is off.

4) It is costly.

5) It is divided into static & dynamic ROM.

• ROM

1) It stands for READ omly memory.

2) It is called dead store permanent memory.

3) It retains contents if power is off.

4) It is cheap.

5) It is divided into PROM,EPROM,EEPROM.

c)Static RAM & Dynamic RAM

• Static RAM

1) It holds the information in HIP-HOP circuit consisting 6 transistors is needed in cache cell.

2) It is costly.

• DYNAMIC RAM

1) It requirs less n.o of transistors per memory cell because intermation is stored in stray capictor.Here only 1 transistor is required to form a memory cell.

2) It is cheap.

d) PROM EPROM & EEPROM

• PROM

1) It stands for Programmable Read Only Memory.

2) It is programmable ROM whose controls can be erased.

• EPROM

1) It stands for Erasable Programmable Read Only Memory.

2) Information stored can be erased in ultra voiled expositive.

• EEPROM

1) It stands for Electrically Erasable Read Only Memory.

2) It's contents can be erased by electricty & again it can be programmed like as EPROM.

• Secondary memory

Floppy disk,Hard disk,cd-rom dvd zip disk,pendrive magnetic tape are secondary memory which are used to store data.These memory are also called bank memory because these memories are used to store data for future applications.

• Floppy disk

IBM launched diskette in market to store data & programme in 1972.It is made up of mylar plastic or poly vinyl plastic.It consists of concrete rings(tracks) & redail sector data.Plastic is covered with iron oxide or barium ferrite when magnetic material is magnetized binary 1 is produced & when domagnetized 0 is produced.It's storing capacity is 1.44 mb & rotates with the speed of 360 RPMC(Revolution Per Minute)

• Hard disk

It is the size of dish washer with 50 platters.Each with a two feet diameter.These platters could hold 160 kb of data.Segate technology announced the first win chester 5.25" hard disk drive in 1980.

Some terms used in Hard disk

• Platters

The platters are located on the both sides with a special materials designed to store data on the forms of magnetic platters.The upper most surface of the lower disk are not used as read/write surface.

The platters are mounted in a stock as a spindle driver by a special motor connected to the spindle which rotate at the high speed.Actulators controls the read write head.

In hard disk

- Winchester technique is employed to seal read/write head & disk.

- It's speed is to 5400 to 1500 rpm.

- Measuring unit is big (like GB)

Hard disk has following advantages over floppy disk

- Hard disk can store large amount of data in terms of GB.

- Hard disk store data for large amount of data in terms of GB.

- Hard disk is procted fromdust smoke & External heat but floppy isn't.

- Data are safely stored in hard disk than that of floppy disk.

Computer memory

The computer is data storing device.There are many catagories of memory namely:primary,secondary,ROM ,RAM,registers,accumulators,floppy,disk,CD-ROM e.t.c.
The processing capacity of computers does not only depends on a capacity or primary memory.A mwmory system can be centralised or distributed.

Centralised
All processors that exists in a system can be shared as one common memory unit which is also preffered as highlycoupled system.
Features:
# In expensive
# Easy to control
# High use of avialable space
Distributed
In this system such processor has a private or local memory as well as common memory.It is also reffered as locely occupied system.
Features:
# Several memory unit can be kept busy at the same time.
# Since each proccesor has its own private memory they can be simultaneously engaged to perform local processing.
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computer memory
Thursday, March 25, 2010

Memory Hierchy
The memory unit is an essential component in any digital computer since it is needed for storing programme & data.The memory unit that communicate directly with cpu is called main memory.
#note:Devices that provide back-up is called auxillary.
The total memory of computer can be the memory in hierchy of components.The memory in hierchy system consists of all storage devices employed in a computer system from the slow flow high capacity auxillary memory through a relatively faster main memory.
A veryhigh speed memory is called cache memory.It is used to increase the speed of processing by making current programs & data one available to cpu at a rapid rate.
The cache memory is employed in computer system to compensate.for speed of differential between main memory acess time & processor logic.
CPU logic is usally faster than main memory acess time with the result that processing speed is limited primarily by the speed of main memory.
A technique used to compensate for mismating in operating speed is to e,ploy an extreamly fast by cache.The cache is used for storing segments of programmes currently being executed in CPU & temporary data frequently needed in the present calculation.
Cache memory
Simply a luffer memory present between processor (CPU) & main memory is called cache memory.It's capacity is measured in unit ratio.
It's charactersticts are:
# Very small in sieze but expensive.
# It is 5-10 times faster than main memory.
# It increases storing capacity of main memory & increase speed of processor.