Computer Number system Note for IBPS PO

Computer Memory Note for IBPS PO

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Computer Memory Note for IBPS PO

Computer Memory

A memory is a hardware device used to store data,information and instructions.This device is capable to store data/information/instructions Temporarily or Permanently.This is one of the most important element in the computer system.

Need of Memory
  • Without memory we can not access or use the software present in the
  • Memory is used to run any
  • Memory is used to hold data/information/instructions permanently or
There are two types of Memory
  • Primary Memory or Main Memory
  • Secondary Memory or Auxiliary Memory

Primary  Memory-Primary  Memory  is  a  memory  used  to  store  data temporarily

and it provide fast retrieval of data.This is the memory that communicates with CPU directly.This memory is used to keep track of current things. This Memory is a Volatile Memory means when the power goes off,it lost all its content forever and after losing we cannot get this data/information again.Note-To overcome from this problem of losing,we use UPS(Uninterrupted Power Supply)as it provide backup support in the mode of Electricity to computer system when power goes off.

There are two types of Primary Memory

  1. RAM
  2. ROM

 RAM – RAM stands for Random Access Memory. Why we call it Random Access Memory as it provide Random access of data.we can access any byte of Memory without touching the its previous bytes. It founds in computer system and any other devices such as printer.

There are two types of RAM

1) RAM-DRAM stands for Dynamic Random Access Memory.This memory is made up of memory cells where each cell is composed of one capacitor and one store each bit in separate capacitor.The capacitor has two states i.e Charged or Discharged which is used to store two  bits   of   data   e   0   or   1.DRAM  needs  to  be  refreshed  periodically  to  store information. This refresh operation occurs thousand of times per second.

  • DRAM is Slower since it needs to be refreshed
  • DRAM is less
  • DRAM occupies less amount of space on the
  • DRAM is a Volatile as it lost all data when power goes
  • DRAM is basically used for Main Memory

2) SRAM-SRAM stands for Static Random Access

  • It retains the data as power is provided to the memory
  • It does not need to be refreshed
  • SRAM is faster than
  • SRAM is expensive than the
  • SRAM uses multiple transistors for each memory cell.It does not use capacitor.
  • SRAM is often used as cache memory due to its high
  • It is also a Volatile

3) ROM-ROM stands for Read Only Memory.

  • It is a Non-Volatile Memory means its data never get lost when power goes
  • ROM provides the facility of Read only
  • In ROM,we can write data or instruction only one
  • ROM chips are designed at the time of manufacturing the computer
  • It cannot be reprogrammed or

There are three types of ROM.

PROM – Programmable ROM

  • It is a device that is programmed only
  • Once programmed,its content can never be
  • It was invented by Wen Tsing Chow in
  • The basic difference between ROM and PROM is that ROM is programmed during the manufacturing whereas PROM is manufactured as a blank memory.To write data in PROM we need a special device that is known as PROM programmer or PROM burner.the process of programming PROM is sometime known as burning

EPROM – Erasable Programmable Read Only Memory.

  • It was invented by “Dov Frohman” of Intel in
  • It is Non Volatile
  • It is the advance version of ROM in which programmer can rewritten data/ Instructions using special
  • Ultra violet light is used to erase the data from the it is also known as
  • A special device is used to rewritten

EEPROM – Electronic Erasable Programmable Read Only Memory.

  • It’s data can be erased electrically, then rewritten electrically.

Secondary Memory –

  • Secondary memory is also known as Auxiliary or External
  • It is used to store large amount of
  • It is a permanent storage
  • It is used as the backup for the data and
  • CPU cannot process data/information stored in the secondary memory or information must first be copied into the main memory or primary memory after that cpu can use or process
  • It is non volatile
  • It is slow as compared to primary
  • Data stored in secondary memory remains in the memory till they are deleted or overwritten by the

Examples:- HDD, CD, DVD, Floppy disk and Pen drive


  • It can store large amount of data up-to 1
  • It is fast.
  1. Floppy Disk-
  • It can store only small amount of
  • It is slower to access than Hard
  • Floppy disk is available in three different
  • sizes.           1)  5.25           – can store up to 1.2 MB

2) 3.5 inch      – can store up to 44 MB

3) 8 inch         – can store up to 80 KB to 242 KB

CD –

  • It stands for Compact
  • Least Expensive
  • There are three categories of
    • CD-ROM – Compact Disk-Read Only Memory
    • CD-R – Compact Disk Record able
    • CD-RW – Compact Disk Re-writable


  • DVD stands for Digital Video is also known as Super Density
  • It has more storage capacity than compact
  • It can store 4.7 GB – 17.08 GB
  • There are three categories of
  1. DVD-ROM
  2. DVD-R
  3. DVD-RW

To read data it uses longer-wavelength red laser

Blue-Ray Disk –

  • Blue ray disk is an optical disk designed to recapture the data normally in DVD format.
  • In blue-ray disk , blue lasers are used to read the disk
  • It contain 25 GB per layer space.It can store almost 5 times more data than a single layer
  • Categories of Blue Ray Disk-
    1. BD-ROM for pre-recorded content
    2. BD-R for PC data Storage
    3. BD-RW for PC data Storage
    4. D-RE for HDTV recording

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Pen Drive –

  • It is very small in
  • It is also known as flesh
  • A flesh drive is a device that consists of flash memory(A memory which retains data in the absence of power supply)with a portable USB
  • Today, Flash drives comes in different capacities as 256MB, 512MB, 1GB, 4GB, 16GB upto

Magnetic Tape –

  • Magnetic tapes can be read,written,erased and
  • Magnetic tapes can be accessed sequentially
  • It is usually 12.5mm to 25mm wide and 500m to 1200 m
  • It stores data up to 1

Memory can also be categorized on the basis of their material :

  • Semiconductor memory:-such as RAM, ROM, EPROM, and flash memory.
  • Magnetic memory: -such as hard disk, floppy disk and magnetic
  • Optical memory: -such as computer disk, DVD and blu-ray
  • A bus, is a set of physical connections (cables, printed circuits, etc.) which can be shared by multiple hardware components in order to communicate with one another.
  • The address bus (sometimes called the memory bus) transports memory addresses which the processor wants to access in order to read or write data. It is a unidirectional bus.
  • The data bus transfers instructions coming from or going to the processor. It is a bidirectional
  • The control bus (or command bus) transports orders and synchronization signals coming from the control unit and travelling to all other hardware components. It is a bidirectional bus, and also transmits response signals from the hardware.

Memory Hierarchy-

  • Computer Memory can be categorised on the basis of two key factors-Capacity-Capacity Access time

Memory Units

  • Bit- The smallest unit to store data is bit. Bit can store only a single information e.True or False.Computer use 0 for False and 1 for True.
  • 1 Nibble = 4 Bit
  • 1 Byte = 8 Bit
  • 1 KB  = 1024 PB                                                                      – 1,024 bytes
  • 1 MB = 1024 KB (KiloByte)                                                  – 1,048,576 bytes
  • 1 GB = 1024 MB (MEGABYTE) = 1024 ZB                       -1,048,576 bytes
  • 1 TB = 1024 GB(Gigabytes)                                                  – 1,099,511,627,776 bytes
  • 1 PB(Petabytes) = 1024 TB(Terabytes)                              -1,125,899,906,842,624 bytes
  • 1 EB(Exa byte) = 1024 PB
  • 1 ZB(ZETTA BYTE)= 1024 EB
  • 1 YB(YOTTA BYTE)= 1024 ZB
  • 1 BRONTO BYTE = 1024 YB
  • 1 GEOP BYTE= 1024 BB

Computer memory Question and Answer

  1. Cache and main memory will lose their contents when the power is off. They are                .

(a) dynamic          (b) static           (c) volatile           (d) non-volatile               (e) faulty

Answer (c)

2.             and are the two types of computer

(a) RAM and CPU     (b) ROM and CPU      (c) RAM and ROM           (d) RAM and BIOS              (e) BIOS and ROM

Answer (c)

3. Which computer bus connects the main memory to the memory controller in computer systems ?

(a) Data Bus     (b) Memory Bus       (c) I/O Bus      (d) Both   ((b) and (c)        (e) None of these

Answer (b)

4. Which of the following memory has stored data in large number?

(a) RAM     (b) ROM     (c) Cache memory      (d) Hard Disk  (e) None of these

Answer (d)

5.                        is designed to communicate instructions to a machine, particularly a It can be used to create programs to control the behavior of a machine or to express algorithms.

(a) PROM               (b) Programming language       (c) Micro-controllers        (d) EPROM                (e) None of the above

Answer (b)

6. A high speed device used in CPU for temporary storage during processing is called

(a) Register     (b) Bus      (c) Compiler      (d) Translator            (e) Bus

Answer (a)

7. When a computer is turned on, where does it get the first instructions that it loads into RAM ?

(a) From RAM        (b) From ROM        (c) From the Hard Disk      (d) From a CD        (e) None of these

Answer (b)

8. Which one of the following is true for RAM ?

a) It is volatile memory       b) It is temporary memory          c)It is primary memory                   d)All of the above

Answer (d)

9.What is the difference between a memory and storage ?

a)Memory is slow and storage is fast             b).Memory is temporary and storage is permanent c) .Memory is permanent and storage is temporary                                                                              d) Memory is non-volatile and storage is volatile

Answer (b)

10. When the computer is turned off then the content of which one of the following is lost ?

a).Output        b).Storage                 c).Memory          d).Register

Answer (c)

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