Computer System Overview

Class 11 - Computer Science with Python Sumita Arora

Checkpoint 1.1

Question 1(i)

Storage of 1 KB means the following number of bytes :

1. 1000

2. 964

3. 1024

4. 1064

Answer

1024

Reason — 1 KB = 1024 bytes

Question 1(ii)

One Megabyte is equivalent to

1. 210 bytes

2. 220 bytes

3. 230 bytes

4. none of the above

Answer

None of the above

Reason — 1 MB = 1024 KB = 1024 * 1024 bytes = 10,48,576 bytes.

Question 2

What are the functional components of a digital computer ?

Answer

The functional components of a digital computer are as follows:

1. Input Unit — It is responsible for taking input for the computer. For example, keyboard.

2. Output Unit — It is responsible for giving output to the user. For example, monitor.

3. Central Processing Unit (CPU) — It is responsible for processing the data and instructions. It has the following sub-components:

   1. Arithmetic and Logic Unit (ALU)

   2. Control Unit (CU)

   3. Registers

4. Primary Memory — It is the internal volatile­ memory where data and instructions are stored during processing.

5. Secondary Storage Unit — It refers to the external storage devices which provide permanent memory to the computer system.

Question 3

What are the components of CPU? What is its role? What is the function of control unit of CPU?

Answer

Central Processing unit is responsible for processing the data and instructions. It has the following sub-components:

1. Arithmetic and Logic Unit (ALU) — It is responsible for carrying out the arithmetic instructions (add, subtract, multiply, divide) and making logic decisions (greater than, less than, equal to).

2. Control Unit — The control unit controls and guides the interpretation, flow and manipulation of all data and information. It acts as a supervisor by controlling and guiding the operation taking place.

3. Registers — The CPU uses these small units of data holding places to temporarily hold some important processing-information during the time the processing is taking place.

Question 4

What role does the input unit play in a computer?

Answer

An input unit takes the input and converts it into binary form so that it can be understood by the computer.

The input unit is formed by the input devices attached to the computer. For example, keyboard, mouse, magnetic ink character reader (MICR), optical mark reader (OMR), optical character reader (OCR), joystick, etc.

Question 5

What is the function of ALU ?

Answer

The ALU performs the following functions:

1. all the four arithmetic operations — addition, subtraction, multiplication and division.

2. some logical operations — less than, greater than, less than equal to, greater than equal to, equal to, not equal to.

Question 6

What role does the output unit play in a computer?

Answer

Output Unit converts the output in binary form to human readable form. The output coming from the CPU is in the form of binary signals which needs conversion in some human readable form i.e,, characters, graphical or audio visual form. This function of conversion is performed by output units.

For example, monitor, speaker etc.

Question 7

What is the function of main memory ? What are the measuring units of memory ?

Answer

The memory of a computer is more like a predefined working place, where it temporarily keeps information and data to facilitate its performance. When the task is performed, it clears its memory and memory space is then available for the next task to be performed.

A bit is an elementary unit of the memory. The smallest unit of memory is a byte (8 bits). A byte can store one character in binary form. Other measuring units are kilobyte (KB) equal to 1024 (210) bytes, Megabyte (MB) equal to 1024 KB, Gigabyte (GB) equal to 1024 MB and Terabyte (TB) equal to 1024 GB.

Question 8

What are different types of ROM ?

Answer

The different types of ROM are:

1. PROM (Programmable ROM)

2. EPROM (Erasable Programmable ROM)

3. EEPROM (Electrically Erasable Programmable ROM)

4. Flash EEPROM

5. Mask ROM

Question 9

What is the role of cache memory ?

Answer

The Cache Memory is a high speed memory available inside CPU in order to speed up access to data and instructions stored in RAM memory. Whenever some data is required, the CPU first looks in the cache, if it is there or not. If the data is found in cache, CPU does not access memory and hence the process becomes very fast.

Question 10

Which storage device is considered a portable device ?

Answer

A flash memory device is considered a portable device.

Checkpoint 1.2

Question 1

What are major functional components of a mobile system ?

Answer

The major functional components of a mobile system are as follows:

1. Mobile Processor (Mobile CPU) — This is the brain of a smartphone. It has two sub-processor types:
   (i) Communications Processing Unit — responsible for making and receiving phone calls.
   (ii) Applications Processing Unit (APU) — responsible for governing, controlling all types of operations taking place on a mobile system by running various apps.

2. Display Subsystem — responsible for providing display facilities, touch sensitive interface and touch sensitive keyboards.

3. Camera Subsystem — designed to deliver a tightly bound image processing package.

4. Mobile System Memory — consists of RAM (work memory) and ROM (mobile's internal storage).

5. Storage — external storage of a mobile system.

6. Power Management Subsystem (Battery) — responsible for providing power to a mobile system.

Question 2

What is the role of communication processor of a mobile system ?

Answer

Communication processor of a mobile system 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.

Question 3

How does a mobile system manage and draw power?

Answer

The Power Management Subsystem is responsible for providing power to a mobile system. The mobile systems work on limited power provided through an attached battery unit. This subsystem 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.

Question 4

What is the role of display management unit of a mobile system ?

Answer

The display management unit of a mobile system is responsible for providing display facilities, touch sensitive interface and touch sensitive keyboards.

Question 5

How does memory of mobile function ?

Answer

A mobile system's memory is comprised of following two types of memories:

1. RAM (Random Access Memory) — It is the work memory of the mobile system. The installed mobile apps, when run, are first loaded in the RAM and then executed. These apps remain in RAM and when you are no longer using them, then, they are shifted to background. RAM does not store information once the device is turned off.

2. ROM (Read Only memory) — The ROM or Read Only Memory is a part of mobile system's internal storage and it is not accessible for users to write on and is thus referred to as Read Only Memory. This ROM part of a mobile system internal storage is where operating system resides. It also has some preinstalled apps in this memory sections which cannot be deleted on users' end either.

Question 6

How does the CPU of a mobile system work?

Answer

A mobile system has to cater to a variety of operations and applications and its CPU has to manage all these. Thus the CPU of a mobile system has many sub-processors that help it control and manage diverse applications. The CPU of a mobile manages all these types of applications and operations:

1. Manages communications while connecting to radio transceivers and SIM.

2. Manages audio through ADC (analog to digital converter) and DAC (digital to analog converter).

3. Manages display and touch sensitive sensors and interface.

4. Works in tandem with memory and storage.

Checkpoint 1.3

Question 1

How can computer software be classified ?

Answer

Computer software can be classified into two categories:

1. System Software — controls internal computer operations.

2. Application Software — set of programs necessary to carry out operations for a specified application.

Question 2

What are two categories of system software ?

Answer

Two categories of system software are as follows:

1. Operating system — acts as an interface between a user and the hardware.

2. Language Processor — responsible for converting an High Level Language code into machine understandable code.

Question 3

What is an operating system ? What is its role ?

Answer

An Operating System is a program which acts as an interface between a user and the hardware. For example, Microsoft Windows 10.

The primary goal of an operating system is to make the computer system convenient to use and secondary goal is to use computer hardware in an efficient manner. It controls all other components of the computer system and coordinates the use of the hardware among the various application programs for the various users.

Question 4

What is application software ? What are the three categories of application software ?

Answer

An Application Software is the set of programs necessary to carry out operations for a specified application. These are the programs written by programmers to enable computer to perform a specific task such as processing words, inventory control, handling calculations and figures etc. For example, Microsoft Word 2013.

The three categories of application software are as follows:

1. Packages — For example, word processing software, spreadsheets, etc.

2. Utilities — For example, text editor, backup utility etc.

3. Customised software — inventory management system, payroll system etc.

Multiple Choice Questions

Question 1

Which of the following components is the main memory of computer ?

1. CD

2. DVD

3. Internal hard drive

4. RAM

Answer

RAM

Reason — RAM is the main memory of the computer.

Question 2

Which component of a computer connects the processor to the other hardware?

1. System Bus

2. CPU

3. Memory

4. Input Unit

Answer

System Bus

Reason — The system bus is an electronic pathway composed of connecting cables that connects the major components of a computer system.

Question 3

Which of the following is referred to the brain of computer ?

1. Processor

2. RAM

3. ROM

4. Hard drive

Answer

Processor

Reason — Processor or CPU is called brain of the computer as it guides, directs, controls and governs the performance of a computer.

Question 4

What is the name of programs that control the computer system ?

1. Hardware

2. Keyboard

3. Software

4. Mouse

Answer

Software

Reason — Software is a set of programs that govern the operation of a computer system.

Question 5

The physical components of a computer are called ?

1. Software

2. Hardware

3. ALU

4. CPU

Answer

Hardware

Reason — Hardware are all the parts of the computer you can see and touch.

Question 6

Which of the following is the common measurement of unit of computer memory?

1. IQ

2. Byte

3. Terabyte

4. Gigabyte

Answer

Terabyte, Gigabyte

Reason — Terabyte and Gigabyte are the common measurement of unit of computer memory.

Question 7

What is the name of the component that is used to both read and write data ?

1. ROM

2. RAM

3. Hard Drive

4. Cache memory

Answer

RAM

Reason — RAM is used to both read and write data.

Question 8

The CPU is also known as :

1. The Brain

2. The Processor

3. The Central Processing Unit

4. All of these

Answer

All of these

Reason — The CPU is also known as the brain of the computer, the processor and the Central Processing Unit.

Question 9

Which smaller unit of the CPU directs and coordinates all activities within it and determines the sequence in which instructions are executed, sending instructions sequence to other smaller unit.

1. CU

2. ALU

3. PROCESSOR

4. All of these.

Answer

CU

Reason — Control unit coordinates all activities within it and determines the sequence in which instructions are executed, sending instructions sequence to other smaller unit.

Question 10

Which smaller unit of the CPU performs all arithmetic and logic functions in a computer ?

1. CU

2. ALU

3. PROCESSOR

4. All of these.

Answer

ALU

Reason — Arithmetic and Logic Unit performs all arithmetic and logic functions in a computer.

Question 11

Component of CPU which is responsible for comparing the contents of two pieces of data is ............... .

1. ALU

2. CU

3. memory

4. register

Answer

ALU

Reason — Arithmetic and Logic Unit is responsible for comparing the contents of two pieces of data.

Question 12

In a computer, CU stands for

1. control unit

2. cache unit

3. calculating unit

4. communication unit

Answer

control unit

Reason — In a computer, CU stands for control unit.

Question 13

Arithmetic and logic unit along with control unit of a computer, combined into a single unit, is known as ............... .

1. central processing unit

2. memory unit

3. I/O unit

4. operating unit

Answer

central processing unit

Reason — Arithmetic and logic unit along with control unit of a computer, combined into a single unit, is known as central processing unit.

Question 14

Word Processor and Desktop Publishing program are the examples of ............... .

1. Hardware

2. software

3. cpu

4. none of these

Answer

software

Reason — Word Processor and Desktop Publishing program are the examples of software.

Question 15

Operating System is an example of ............... .

1. Application Software

2. System software

3. Utility program

4. None of these

Answer

System software

Reason — Operating System is an example of System software.

Question 16

A disk fragmentor is an example of ............... .

1. Application Software

2. System software

3. Utility program

4. none of these

Answer

Application Software / Utility program

Reason — A disk fragmentor is an example of utility program. Since utility program is a sub-category of application software, hence it is classified as an application software as well.

Question 17

Flash memory and Blu Ray disk are the examples of ............... .

1. Hardware

2. software

3. cpu

4. none of these

Answer

Hardware

Reason — Flash memory and Blu Ray disk are the examples of hardware.

Question 18

Flash memory is a type of ............... memory.

1. Primary

2. RAM

3. secondary

4. all of these

Answer

secondary

Reason — Flash memory is a type of secondary memory.

Question 19

Which of the following memory types will store the data or information permanently?

1. RAM

2. cache

3. Flash Memory

4. Hard disk

Answer

Flash Memory, Hard disk

Reason — Flash Memory and Hard disk are external storage devices and hence they will store the data or information permanently.

Question 20

Which of the following memory types cannot store the data or information permanently ?

1. RAM

2. cache

3. Flash Memory

4. Hard disk

Answer

RAM

Reason — RAM is a volatile memory and loses all its data when the power is turned off.

Fill in the Blanks

Question 1

Computer organisation refers to the logical structure of a computer describing their interconnections and dependency.

Question 2

RAM and ROM are the types of internal/primary/main memory.

Question 3

The Arithmetic and Logic Unit (ALU) is responsible for carrying out arithmetic and logic operations.

Question 4

The Control Unit (CU) of the CPU controls or supervises the processing taking places.

Question 5

The small memory providing units inside the CPU are called the registers.

Question 6

The cache memory is a special high speed memory storing the most recently accessed data.

Question 7

The power unit of a mobile system is called battery.

Question 8

The set of programs necessary to carry out operations/tasks pertaining to a specific application, are called application software.

Question 9

Software that controls and manages internal computer operations is called system software.

Question 10

Utility programs are a type of application software.

Question 11

Antivirus software is a type of application software.

Question 12

Windows OS is a type of system software.

True/False Questions

Question 1

A computer system consists of both hardware and software.
True

Question 2

Hardware is a set of instructions called programs that the computer uses to carry out tasks while Software are all the parts of the computer you can see and touch, also known as peripherals.
False

Question 3

The two smaller units of the Processor are CU and ALU.
True

Question 4

Main Memory holds data and instructions being processed by the computer and is directly accessible by the CPU.
True

Question 5

A mobile system also contains a CPU.
True

Question 6

A mobile system works with electricity.
False

Question 7

A mobile system has its own little power unit.
True

Question 8

A cache memory is a type of RAM.
True

Question 9

Language processors are a type of application software.
False

Question 10

Customised software is a type of system software.
False

Assertions and Reasons

Question 1

Assertion. A computer can deliver performance only through an efficient combination of hardware and software.

Reason. While hardware refers to the physical electronics equipment, software are the recorded programs that govern the hardware to perform tasks in a computer.

Answer

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation

If the hardware is inefficient, the best optimized software will also perform poorly on it and a poor software can degrade the performance of the best most efficient hardware. Hence, both need to be efficient for the computer to deliver best performance.

Question 2

Assertion. The CPU of a computer uses registers as memory.

Reason. Registers are small data holding areas within CPU that hold data, instructions etc. during the processing.

Answer

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation

The CPU uses registers to temporarily hold some important information during the time the processing is taking place.

Question 3

Assertion. The primary memory is volatile memory as all its contents get erased as soon as the power goes off.

Reason. The cache memory is also a primary memory.

Answer

(b)

Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

Explanation

Primary memory is temporary as it is lost when power goes off. Cache memory is also temporary.

Question 4

Assertion. A part of main memory is non-volatile too.

Reason. ROM is a read only memory with some pre-written instructions, which are retained even after power is off.

Answer

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation

ROM is the non-volatile part of the main memory.

Question 5

Assertion. Not all types of software are system software.

Reason. Application software are designed to carry out operations for a specific application.

Answer

(b)

Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

Explanation

The classification of Software into categories and sub-categories is as follows:

1. System Software

   1. Operating System

   2. Language Processor

2. Application Software

   1. Packages

   2. Utilities

   3. Customised Software

   4. Developer Tools

Question 6

Assertion. An operating system is a system software.

Reason. The software that controls internal computer operations, is called system software.

Answer

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation

An operating system controls all other components of a computer system and acts as an interface between a user and the hardware.

Question 7

Assertion. Customised software is a tailor made software according to user's requirements.

Reason. Software libraries are customised software.

Answer

(c)

Assertion is true but Reason is false.

Explanation

Software libraries are not customised software. Software libraries are set of pre-written code/functions/classes etc. available to programmers for use in the development of new code.

Question 8

Assertion. Utility software programs are application software.

Reason. Application software are the programs necessary to carry out operations for specific applications.

Answer

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation

Utility software are those application programs that assist the computer by performing housekeeping functions like backing up disk or scanning / cleaning viruses or arranging information, etc.

Assignment Questions

Question 1

Briefly explain the basic architecture of a computer.

Answer

A computer system comprises of five basic components:

1. Input Unit — An input unit takes the input and converts it into binary form so that it can be understood by the computer. For example, keyboard, mouse etc.

2. Output Unit — It converts the output in binary form to human readable form. For example, monitor, speakers etc.

3. Central Processing Unit (CPU) — It is responsible for processing the data and instructions. It consists of two parts:

   1. Arithmetic and Logic Unit (ALU) — It performs all the four arithmetic operations (addition, subtraction, multiplication and division) and some logical operations (less than, greater than, less than equal to, greater than equal to, equal to, not equal to).

   2. Control Unit (CU) — It acts as a supervisor by controlling and guiding the operation taking place.

4. Primary Memory — It is the internal volatile­ memory where data and instructions are stored during processing. It is of two types: Random Access Memory (RAM) and Read Only Memory (ROM).

5. Secondary Storage Unit — It refers to the external storage devices which provide permanent memory to the computer system. For example, hard disk, compact disk, flash drive etc.

Question 2

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

Answer

An input unit takes the input and converts it into binary form so that it can be understood by the computer.

Since a computer operates on electricity, it can understand only the language of electricity i.e., either ON or OFF or High/Low voltage or the binary language that uses just two symbols: 1 for ON and 0 for OFF. It cannot understand the the data and instructions if they are not in binary language. Thus, input unit takes data and instructions from the user and converts them into binary form so that the computer can understand them.

Different input devices take input in different forms and pass them in digital form to CPU for processing. Computer inputs may consist of:

1. letters, digits, commands from the keyboard.

2. movement of pointer using a mouse or pointing device.

3. sound input from a microphone.

Question 3

What is the function of CPU in a computer system ? What are its subunits ?

Answer

The CPU or the Central Processing Unit is the main control centre and processing unit. It is also called brain of the computer as it guides, directs, controls and governs the performance of a computer.

The CPU has three sub-components which are as follows:

1. Arithmetic and Logic Unit (ALU) — It is responsible for carrying out the arithmetic instructions (add, subtract, multiply, divide) and making logic decisions (greater than, less than, equal to).

2. Control Unit — It is responsible for controlling and supervising the processing.

3. Registers — The CPU uses these small units of data holding places to temporarily hold some important processing-information during the time the processing is taking place.

Question 4

What functions are performed by the control unit ? Can we call it the control centre of computer system ? Why ?

Answer

Control Unit is responsible for controlling and supervising the processing. It performs the following functions:

1. It controls and guides the interpretation, flow and manipulation of all data and information.

2. It sends control signals until the required operations are done properly by ALU and memory.

3. It fetches the program instructions from the memory unit one by one. The instructions are decoded and executed one after the other.

4. After an instruction is executed, it sends a signal to memory to send the next instruction in sequence to CU.

5. It controls the flow of data from input devices to memory and from memory to output devices.

Yes, we can call control unit the control centre of computer system because it acts as a supervisor by controlling and guiding all the other components of the computer system as well as the operations taking place.

Question 5

What functions are performed by the ALU ? Is it an independent unit ? If not, which unit does ALU work in coordination with ?

Answer

Arithmetic and Logic unit is responsible for carrying out the arithmetic instructions (add, subtract, multiply, divide) and making logic decisions (greater than, less than, equal to).

No, it is not an independent unit. It is a part of CPU. It works in coordination with the commands given by the Control Unit.

Question 6

Distinguish between CPU and ALU.

Answer

CPU

ALU

CPU refers to Central Processing Unit.

ALU refers to Arithmetic and Logic unit.

CPU is one of the main components of a computer system.

ALU is a sub-unit of the CPU.

CPU guides, directs, controls and governs the performance of a computer.

ALU carries out arithmetic and logic operations on the operands in computer instructions.

Question 7

What is the function of output unit in a computer system ? Give examples of some output devices.

Answer

Output Unit converts the output in binary form to human readable form. The output coming from the CPU is in the form of binary signals which needs conversion in some human readable form i.e,, characters, graphical or audio visual form. This function of conversion is performed by output units.

Examples of some output devices are monitor, speaker, printers, plotters etc.

Question 8

What role does memory play in the functioning of computer system ?

Answer

The memory of a computer is more like a predefined working place, where it temporarily keeps information and data to facilitate its performance. When the task is performed, it clears its memory and memory space is then available for the next task to be performed.

There are two types of main memory:

1. Random Access Memory

2. Read Only Memory

Since computer's main memory is temporary, secondary memory space, such as hard disk, CDs, pen drive etc., is needed to store data and information permanently for later use.

Question 9(a)

Define byte.

Answer

A bit is an elementary unit of the memory. Eight bits together form a byte.

Question 9(b)

Define kilobyte.

Answer

A kilobyte is equal to 210 bytes i.e., 1024 bytes.

Question 9(c)

Define megabyte.

Answer

A megabyte is equal to 210 kilobytes i.e., 1024 kilobytes.

Question 9(d)

Define gigabyte.

Answer

A gigabyte is equal to 210 megabytes i.e., 1024 megabytes.

Question 9(e)

Define terabyte.

Answer

A terabyte is equal to 210 gigabytes i.e., 1024 gigabytes.

Question 10

What is the meaning of the term volatile primary memory ? What can be done to overcome the problems of volatility ?

Answer

Volatile primary memory means that when the power goes off, the contents of the primary memory get erased.

Since computer's primary memory is volatile or temporary, secondary memory space is used to store data and information permanently for later use. Secondary storage media are the hard disk, CD-RWs, pen drive etc.