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.