lec 6 memory

WELCOME

MIS – 104:

Computing Fundamentals

BBA Department of MISUniversity of Dhaka

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Books

1. Introduction to Computer Peter Norton

2. Computer Fundamentals Dr. M Lutfar Rahman

3. Computer Fundamentals Pradeep K. Sinha

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Previous class

>>Organization of computerInput UnitOutput UnitMemory unitControl UnitALU

Today’s Class

Memory Unit

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Memory

Memory: – One or more set of chips that stores data or

programmed instructions either temporarily or permanently.

Classification of memory:1. Primary memory2. Secondary memory

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Location of different memories

ALU

MAIN MEMORYOR

RESISTERS

CONTROL UNITINPUT

UNITOUTPUT

UNIT

SECONDARY MEMORY

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Calculations of storage capacity

01 BYTE (B) 08 bit

01KB 1024 B

01 MB 1024.1024 B

01 GB 1024.1024.1024 B

01 TB 1024.1024.1024.1024 B

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Memory Terminologies

• Memory Address:– Memory locations are

identified by numbers 100

B

X

Y

A0000

0001

0002

FFFD

FFFE

FFFF

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• Memory Word:– When memory is read or written, a block of

bit is read or written instead of a single bit.

– The block is considered to be a unit of operation/processing

– A set of bit with which read/write operation is done in a certain storage device is called memory word

– Example: 08 bits or 01 Byte memory word clearly 01000000 (08 bits) represents 64 and its character is @; here, this digital 08 bits in combine known as a memory word

100

B

X

Y

A0000

0001

0002

FFFD

FFFE

FFFF

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• Destructive:– composed of capacitors, data disappears when

read operation is done, needs re-write operation to retain data

• Non-destructive: – reverse nature – Example: semiconductor, switch, flash memory,

pen drive

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• Volatile:– Type of memory where data remains only when

the power supply is on. – Ex-RAM

• Non-volatile:– here content remains even the power is turned off– Example: hard disk, floppy disk, flash drive etc

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Memory Terminologies:Memory operation

• Memory store/write:– The process of storing or writing data at the

specific location of the memory– Data is stored as bits – Ex- CD writing operation

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Memory Terminologies:Memory operation

• Memory read: – Also called ‘fetch operation’– To read stored data or to process that stored data– A binary word is selected from a specific address

of memory and this is transferred to another device

– Example: To hear a song from CD or any drive

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Memory Terminologies:Memory access

• Random access:– Any location of storage can be accessed at any

moment– Does not matter whether the desired access

location is too close or a far away– Consumes almost same amount of time– Found in primary and secondary memory

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Memory Terminologies:Memory access

• Sequential:– accessing a bit of information in a serial order,

one after another– Access time depends on the last

order/information execution time– Example: Off line storage such as playing a song

from magnetic tape

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Primary memory

• Includes RAM & ROM

• CPU access directly on this memory

• Normally volatile in nature

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Primary memory: RAM

• Central storage unit

• Volatile

• Temporary in nature

• Holds operating systems, application programme, data in current use

• Other name is (Read/Write) memory

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Different types of RAM

• S RAM- Exhibits data remanance but still volatile as data dissolves when turn off

• D RAM- Data disappears after a certain period automatically if it is not refreshed. This type of RAM needs periodically re-read or re-written. Ex- Z-RAM, TT-RAM, A-RAM

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Primary memory: ROM

• Proportionally read operation is more than write operation

• Contains user programmed instructions like Bootstrap loader

• Non-volatile

• permanent

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Different types of ROM

ROM

Mask ROM PROM EPROM EEPROM

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Secondary memory

• Auxiliary unit• Storing capacity is huge• Normally non-volatile

• Normally two types-1. Magnetic 2. Optical

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Secondary memory: Magnetic

• Variation of ‘Magnet polarity’ determines whether the bit will be 0 or 1

• Data write process is done by electromagnetic head

• Ex- hard disk, floppy disk, magnetic tape

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Secondary memory: Optical

• Variation of light reflection determines the nature of bits

• Data is written with the help of LASER or UV rays

• Ex-CD-R/RW, DVD-R/RW, BD-R

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Memory address:

• It is a number or a set of digital number (bit/Bytes) in the memory

• This address specially represented by binary numbers

• Decimal, Octal, Hex-decimal numbers are also used for addressing

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Virtual memory:

• When secondary memory is used as primary memory then this is called virtual

• Provide assistance to the RAM, by creating space for the great amount of data

• When RAM finishes it’s access, virtual memory vanishes

• Virtual memory can be selected by user

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Cache memory:

• Small memory chip is attached between CPU & main memory

• Give the assistance to the resisters• Speed up the data process• Three types of cache memory is found e.g.

L1(CPU resident), L2 & L3 (mother board)

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Resisters

• They are not the part of main memory but store data and pass as directed by CPU

• The size of the resisters which is sometimes called the word size,indicates the amount of data with which CPU can work/access.

• Ex- 32 bits processor means, 04 bytes data processing capability

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