Introduction to Computers

M. Tawfiqul Islam, Lecturer, CSE, DU Books Introduction to Computer Peter Norton 2. Computer Fundamentals Dr. M Lutfar Rahman 3. Computer Fundamentals Pradeep K. Sinha M. Tawfiqul Islam, Lecturer, CSE, DU

Memory Unit

M. Tawfiqul Islam, Lecturer, CSE, DU Memory Memory: One or more set of chips that stores data or programmed instructions either temporarily or permanently. Classification of memory: Primary memory Secondary memory M. Tawfiqul Islam, Lecturer, CSE, DU

Location of different memories ALU MAIN MEMORY OR RESISTERS CONTROL UNIT INPUT OUTPUT SECONDARY MEMORY M. Tawfiqul Islam, Lecturer, CSE, DU

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

M. Tawfiqul Islam, Lecturer, CSE, DU Memory Terminologies Memory Address: Memory locations are identified by numbers 100 B X Y A 0000 0001 0002 FFFD FFFE FFFF M. Tawfiqul Islam, Lecturer, CSE, DU

M. Tawfiqul Islam, Lecturer, CSE, DU 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 A 0000 0001 0002 FFFD FFFE FFFF M. Tawfiqul Islam, Lecturer, CSE, DU

M. Tawfiqul Islam, Lecturer, CSE, DU 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 M. Tawfiqul Islam, Lecturer, CSE, DU

M. Tawfiqul Islam, Lecturer, CSE, DU 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 M. Tawfiqul Islam, Lecturer, CSE, DU

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 M. Tawfiqul Islam, Lecturer, CSE, DU

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 M. Tawfiqul Islam, Lecturer, CSE, DU

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 M. Tawfiqul Islam, Lecturer, CSE, DU

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 M. Tawfiqul Islam, Lecturer, CSE, DU

M. Tawfiqul Islam, Lecturer, CSE, DU Primary memory Includes RAM & ROM CPU access directly on this memory Normally volatile in nature M. Tawfiqul Islam, Lecturer, CSE, DU

M. Tawfiqul Islam, Lecturer, CSE, DU 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 M. Tawfiqul Islam, Lecturer, CSE, DU

M. Tawfiqul Islam, Lecturer, CSE, DU 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 M. Tawfiqul Islam, Lecturer, CSE, DU

M. Tawfiqul Islam, Lecturer, CSE, DU Primary memory: ROM Proportionally read operation is more than write operation Contains user programmed instructions like Bootstrap loader Non-volatile permanent M. Tawfiqul Islam, Lecturer, CSE, DU

M. Tawfiqul Islam, Lecturer, CSE, DU Different types of ROM ROM Mask ROM PROM EPROM EEPROM M. Tawfiqul Islam, Lecturer, CSE, DU

M. Tawfiqul Islam, Lecturer, CSE, DU Secondary memory Auxiliary unit Storing capacity is huge Normally non-volatile Normally two types- Magnetic Optical M. Tawfiqul Islam, Lecturer, CSE, DU

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 M. Tawfiqul Islam, Lecturer, CSE, DU

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 M. Tawfiqul Islam, Lecturer, CSE, DU

M. Tawfiqul Islam, Lecturer, CSE, DU 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 M. Tawfiqul Islam, Lecturer, CSE, DU

M. Tawfiqul Islam, Lecturer, CSE, DU 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 M. Tawfiqul Islam, Lecturer, CSE, DU

M. Tawfiqul Islam, Lecturer, CSE, DU 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) M. Tawfiqul Islam, Lecturer, CSE, DU

M. Tawfiqul Islam, Lecturer, CSE, DU 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 M. Tawfiqul Islam, Lecturer, CSE, DU

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