Computer Memory and storage

Computer Memory and storage

The storage unit of a computer system holds (or stores) the following :

  • Data and instructions required for processing (received from input devices)
  • Intermediate results of processing
  • Final results of processing, before they are released to an output device

Types of Memory

  • Cache Memory
  • Primary Memory
  • Secondary Memory

Primary storage

  • Used to hold running program instructions
  • Used to hold data, intermediate results, and results of ongoing processing of job(s)
  • Fast in operation
  • Small Capacity
  • Expensive
  • Volatile (looses data on power dissipation)

Secondary storage

  • Used to hold stored program instructions
  • Used to hold data and information of stored jobs
  • Slower than primary storage
  • Large Capacity
  • Lot cheaper that primary storage
  • Retains data even without power

Cache Memory

Cache memory is a very high speed semiconductor memory which can speed up the CPU. It acts as a buffer between the CPU and the main memory. It is used to hold tho data and program which are most frequently used by the CPU. The parts of data and programs are transferred from the disk to cache memory by the operating system, from where the CPU can access them.

Primary Memory (Main Memory)

Primary memory is also known as main memory or may also refer to "Internal memory. Primary memory holds only those data and instructions on which the computer is currently working. It has a limited capacity and data is lost when power is switched off. It is generally made up of semiconductor device. These memories are not as fast as registers. The data and instruction required to be processed resides in the main memory. It is divided into two subcategories RAM and ROM.

Characteristics of Main Memory

  • These are semiconductor memories.
  • It is known as the main memory.
  • Usually volatile memory.
  • Data is lost in case power is switched off.
  • It is the working memory of the computer.
  • Faster than secondary memories.
  • A computer cannot run without the primary memory. 

Secondary Memory

This type of memory is also known as external memory or non-volatile. It is slower than the main memory. These are used for storing data/information permanently. CPU directly does not access these memories, instead they are accessed via input-output routines. The contents of secondary memories are first transferred to the main memory, and then the CPU can access it. For example, disk, CD-ROM, DVD, etc.  

1. Magnetic storage media:  
Magnetic media is coated with a magnetic layer which is magnetized in clockwise or anticlockwise directions. When the disk moves, the head interprets the data stored at a specific location in binary 1s and 0s at reading. Examples: hard disks, floppy disks and magnetic tapes

Floppy Disk: A floppy disk is a flexible disk with a magnetic coating on it. It is packaged inside a protective plastic envelope. These are one of the oldest type of portable storage devices that could store up to 1.44 MB of data but now they are not used due to very less memory storage. 

Hard disk: A hard disk consists of one or more circular disks called platters which are mounted on a common spindle. Each surface of a platter is coated with a magnetic material. Both surfaces of each disk are capable of storing data except the top and bottom disk where only the inner surface is used. The information is recorded on the surface of the rotating disk by magnetic read/write heads. These heads are joined to a common arm known as access arm.  

2. Optical storage media:
In optical storage media information is stored and read using a laser beam. The data is stored as a spiral pattern of pits and ridges denoting binary 0 and binary 1.Examples: CDs and DVDs blu ray disc.   

Compact Disk: A Compact Disc drive(CDD) is a device that a computer uses to read data that is encoded digitally on a compact disc(CD). A CD drive can be installed inside a computer’s compartment, provided with an opening for easier disc tray access or it can be used by a peripheral device connected to one of the ports provided in the computer system.A compact disk or CD can store approximately 650 to 700 megabytes of data. 

DVD: It stands for Digital Versatile Disk or Digital Video Disk. It looks just like a CD and use a similar technology as that of the CDs but allows tracks to be spaced closely enough to store data that is more than six times the CD’s capacity. It is a significant advancement in portable storage technology. A DVD holds 4.7 GB to 17 GB of data.  

Blue Ray Disk: This is the latest optical storage media to store high definition audio and video. It is similar to a CD or DVD but can store up to 27 GB of data on a single layer disk and up to 54 GB of data on a dual layer disk. While CDs or DVDs use red laser beam, the blue ray disk uses a blue laser to read/write data on a disk. 

Solid State Memories: Solid-state storage devices are based on electronic circuits with no moving parts like the reels of tape, spinning discs etc. Solid-state storage devices use special memories called flash memory to store data. Solid state drive (or flash memory) is used mainly in digital cameras, pen drives or USB flash drives. 

Pen Drives: Pen Drives or Thumb drives or Flash drives are the recently emerged portable storage media. It is an EEPROM based flash memory which can be repeatedly erased and written using electric signals. This memory is accompanied with a USB connector which enables the pendrive to connect to the computer. They have a capacity smaller than a hard disk but greater than a CD 

Memory Card: A memory card is a type of storage device that is used for storing media and data files. It provides a permanent and non-volatile medium to store data and files from the attached device. Memory cards are commonly used in small, portable devices, such as cameras and phones.A memory card is also known as a flash card. most memory cards today range in size from as small as 4 GB (gigabyte) up to as large as 128 GB. 

Solid State Drive: An SSD is a storage medium that uses non-volatile memory as a means of holding and accessing data. an SSD has no moving parts which gives it advantages such as faster access time, noiseless operation, higher reliability, and lower power consumption. SSDs have become suitable replacements for a standard hard drive in both desktop and laptop computers. 

Qus. What is volatile memory?

Ans: RAM is known as Volatile Memory because when we switch off the computer its data is vanished.

Qus. Define each of the following:

(a) byte (b) kilobyte (c) megabyte (d) gigabyte (e) terabyte


(a) byte: This is the unit of memory in computer. 1 byte = 8 bits

(b) kilobyte: This is the unit of memory in computer. 1 kilobyte = 1024 bytes

(c) megabyte: This is the unit of memory in computer. 1 megabyte = 1024 kilobytes

(d) gigabyte: This is the unit of memory in computer. 1 gigabyte = 1024 megabytes

(e) terabyte: This is the unit of memory in computer. 1 terabyte = 1024 gigabytes.

Qus. State the basic units of computer. Name the subunits that make up the CPU, and give the function of each of the unit.

Ans: Basic units of computer are Input Unit, Central Processing Unit and Output Unit. Sub unites of CPU are Arithmetical Logical Unit(ALU), Control Unit (CU) and Memory Unit(MU).

Qus. What is the function of memory? What are its measuring units?

Ans: The computer memory is a temporary storage area. It holds the data and instructions that the Central Processing Unit (CPU) needs. Before a program can run, the program is loaded from some storage medium into the memory. This allows the CPU direct access to the program. Its measuring units are byte, kilobyte, megabyte, gigabyte, terabyte etc.

Qus. Why is primary memory termed as „destructive write‟ memory but „non-destructive read‟ memory?

Ans: The primary memory is called destructive write because the data enter here are temporary. That‘s why your RAM gets cleared after every restart.

Qus. What is the role of CPU of a mobile system?

Ans: A mobile processor is found in mobile computers and cellphones. A CPU chip is designed for portable computers, it is typically housed in a smaller chip package, but more importantly, in order to run cooler, it uses lower voltages than its desktop counterpart and has more sleep mode capability. A mobile processor can be throttled down to different power levels or sections of the chip can be turned off entirely when not in use. Further, the clock frequency may be stepped down under low processor loads. This stepping down conserves power and prolongs battery life.

Qus. What is SoC? how it is different from CPU? Why is it considered a better development?

Ans: A system on a chip (SoC) combines the required electronic circuits of various computer components onto a single, integrated chip (IC). SoC is a complete electronic substrate system that may contain analog, digital, mixed-signal or radio frequency functions. Its components usually include a graphical processing unit (GPU), a central processing unit (CPU) that may be multi-core, and system memory (RAM). Because SOC includes both the hardware and software, it uses less power, has better performance, requires less space and is more reliable than multi-chip systems. Most system-on-chips today come inside mobile devices like smartphones and tablets.

Qus. Briefly explain the basic architecture of a computer.

Ans: Computer organization refers to logical structure of a computer describing how its components are connected to one another, how they affect one another‘s functioning and contributes to overall performance of computer.

Computers follow the 'IPO' principal i.e. Input ->Process -> Output

(That means a certain input is processed to Generate specific output)

Qus. What do you understand by input unit? What is its significance? What does computer system consist of?

Ans: Input unit is formed by the input devices(Keyboard, mouse, MICR, OBCR etc.) attached to the computer. Input unit is responsible for taking input and converting it into computer understandable form(the binary code). Some common input devices are:

(i) Keyboard

(ii) Mouse

(iii) Microphone

(iv) Scanner

(v) Webcam

(vi) Optical Bar Code Reader

(vii) Optical Mark Reader

(viii) Magnetic Ink Character Reader

(ix) Touch Pad

(x) Track Ball

(xi) Joy stick

(xii) Touch Screen

(xiii) Biometric Sensors. Etc.

Qus. What is the function of CPU in a computer system? What are its sub units?

Ans: The central processing unit (CPU) of a computer is a piece of hardware that carries out the instructions of a computer program. It performs the basic arithmetical, logical, and input/output operations of a computer system. The CPU is like the brains of the computer - every instruction, no matter how simple, has to go through the CPU. So let's say you press the letter 'k' on your keyboard and it appears on the screen - the CPU of your computer is what makes this possible. The CPU is sometimes also referred to as the central processor unit, or processor for short. So when you are looking at the specifications of a computer at your local electronics store, it typically refers to the CPU as the processor. Its sub units are:

(i) Control Unit (ii) Arithmetical and Logical Unit (ALU) (iii) Memory Unit

Qus. What functions are performed by the control unit?

Ans: The CU controls and guides the interpretation, flow and manipulation of all data and information. CU sends control signals until the required operations are done properly by ALU and memory. Another function of CU is the program execution. It means carrying out all the instructions stored in the program. CU gets program instruction from the memory and executes them one after the other. CU acts as a supervisor by controlling and guiding the operation taking place.

Qus. Distinguish between CPU and ALU?

Ans: Difference Between ALU and CPU is that arithmetic logic unit (ALU), another component of the processor, performs arithmetic, comparison, and other operations. While Processor also central processing unit (CPU), interprets and carries out the basic instructions that operate a computer.

The main difference between CPU and ALU is that the CPU is an electronic circuit that handles instructions to operate the computer while the ALU is a subsystem of the CPU that performs arithmetic and logical operations.

Qus. What is the function of output unit in a computer

Ans: Input devices are the hardware that give computers instructions. Output devices relay the response from the computer in the form of a visual response (monitor), sound (speakers) or media devices (CD or DVD drives). The purpose of these devices is to translate the machine's response to a usable form for the computer user.

Qus. Distinguish between internal and external memory.

Ans: Internal memory is usually chips or modules that you attach directly to the motherboard. Internal Memory is a circular disc that continuously rotates as the computer accesses its data. External memory often comes in the form of USB flash drives; CD, DVD, and other optical discs; and portable hard drives.

Qus. What are RAM and ROM? How are they alike? How are they different? What are PROM, EPROM, EEPROM?

Ans: A ROM chip is a non-volatile storage medium, which means it does not require a constant source of power to retain the information stored on it.

A RAM chip is volatile, which means it loses any information it is holding when the power is turned off.

Both of them are known as primary memory as they can directly work with CPU.

Read Only Memory (ROM)

Programmable Read Only Memory (PROM)

Erasable Programmable Read Only Memory (EPROM)

Electrically Erasable Programmable Read Only Memory (EEPROM)

Qus. What are major functional components of a mobile system?

Ans: Major functional components of a mobile system are-

(i) Mobile Processor

a. Communications Processing Unit

b. Application Processing Unit

c. GPU (Graphics Processing Unit)

(ii) SoC (System on a chip)

(iii) Display Subsystem

a. Display Screen

b. Touch Sensitive Interface

c. Touch Sensitive Keyboards

(iv) Camera Subsystem

(v) Mobile System Memory

a. RAM

b. ROM

(vi) Storage

(vii) Power Management Subsystem

Qus. Draw a block diagram depicting organization of a mobile system.

Qus. What is the role of Power Management Unit in a mobile system?

Ans: This subsystem is responsible for providing power to a mobile system. The mobile systems work on limited power provided through an attached battery unit. This system has a battery management system that works with a battery charger and a battery unit and provides power to the mobile system in required form.

It also contains a collection of different functions like battery charging, monitoring and supplying many different voltages these systems require. It also contains software controlled turn-on and turn-off feature to optimize the power consumption and battery life.

Qus. What does the communication processor do?

Ans: this subsystem is responsible for making and receiving phone calls on a mobile handset. It has a digital signal processor that helps it work with RF Transceiver and the Audio subsystem.

Qus. What is GPU? How is it useful?

Ans: Graphics Processing Unit assists the CPU by handling the visuals, other graphically-rich applications. In short, GPU handles all graphics-related chores of a mobile CPU.


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