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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 numbers100
B
X
Y
A0000
0001
0002
FFFD
FFFE
FFFF
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Memory Terminologies
• 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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Memory Terminologies
• 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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Memory Terminologies
• 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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