2074-Solution of Computational Course (Computer Science) : Short Answer Question

Short Answer Question

Attempt any FIVE questions.

4) How conversion from decimal to octal and octal to decimal is done? Illustrate with suitable example. (6)

Ans:

Decimal number can be converted to octal by following procedure:

1. Divide the given number by 8,
2. Write the quotient under the number. Now it becomes new number,
3. Write the remainder in right side,
4. Repeat step (a) to (c) until 0 is produced as the new number,
5. The number written as remainder in reverse order (i.e. bottom to the top) is the required octal number.

Example:

Convert 128 to octal form.

Solution:

8	128
8	16	0 ( as 8*16 is 128 so remainder is zero)
8	2	0 (as 8*2 is 16 so remainder is zero)
	0	2 (as 8*0 is 0 so remainder is two)

 So, the octal form of decimal (128)₁₀ is (200)₈. (from bottom to the top)

Octal number can be converted to decimally following procedure:

1. Write the octal digit as power of 8 increasing from right to left starting from zero.
2. Convert each power of 8 into its decimal equivalent term.
3. Add these terms to give the decimal number.

Example:

Convert 200 to decimal form.

Solution:

=2*8²+0*8¹+0*8⁰

=2*64+0*8+0*1

=128+0+0

=128

So, the decimal form of octal (200)₈ is (128)₁₀.

5) What is CPU? How CPU works in a computer? (6)

Ans:

A central processing unit (CPU), also called a central processor or main processor, is the electronic circuitry within a computer that executes instructions that make up a computer program. The CPU performs basic arithmetic, logic, controlling, and input/output (I/O) operations specified by the instructions in the program.

CPU has three following components:

1. memory or storage unit
2. Control unit
3. Arithmetic logic unit (ALU)

At its core, a CPU takes instructions from a program or application and performs a calculation. This process breaks down into three key stages: Fetch, decode, and execute. A CPU fetches the instruction from RAM, decodes what the instruction actually is, and then executes the instruction using relevant parts of the CPU.

The executed instruction, or calculation, can involve basic arithmetic, comparing certain numbers together, or moving them around in memory. Since everything in a computing device is represented by numbers, those simple tasks equate to what a CPU does. It’s what facilitates everything from starting up Windows, to watching a YouTube video

6) What is data transmission media? How radio wave signal differs from the microwave signal? (1+5)

Ans:

Transmission media is a pathway that carries the information from sender to receiver. We use different types of cables or waves to transmit data. Data is transmitted normally through electrical or electromagnetic signals. There are 2 types of transmission media. They are:

1. Bounded or guided transmission media
2. Unbounded or unguided transmission media

Radio-wave signal	Microwave signal
The frequency of radio wave signal is 3MHz to 300MHz.	The frequency of microwave is 300MHz to 300GHz.
Most of the circuit element are made up of lumped components.	It has distributed circuit element.
Radio-wave signal are good at broadcasting to many people.	Microwave signal are good at point-to-point communication.
Transmitter and receiver must not be in line of sight.	Transmitter and receiver must be in line of sight.
Mainly used for mobile radio communication purpose.	Used in radars, micro ovens, astronomy and industries.

7) What is multimedia system? Briefly discuss the characteristics of multimedia. (1+5)

Ans:

A multimedia system is a system that is capable of processing multimedia data and applications. One of the main requirement of multimedia system is a real time operation. The different components of multimedia are text, image, audio, video and animation.

Following are the characteristics of multimedia:

1. Computer Controlled - Multimedia system is computer controlled. Components of computer multimedia such as audio, video, text, images and animation are computer controlled. User provide command and with the help of multimedia, computer system interprets output.
   So multimedia must be computer controlled.
2. Integrated - Multimedia is used in many applications. Different components of multimedia integrate and operate to provide desirable procedure and outputs. For example, when we open a webpage, text, image, audio, animation and video integrates smoothly to provide better experience to user.
   So multimedia system are integrated.
3. Digitally - Multimedia is digitally operated. The different information they handle must be digital. We cannot represent all components of multimedia without using digital platforms.
   So information they handle must be digitally represented.
4. Interactive - The use of multimedia components without their interaction do not fulfill the objective of multimedia. It should be interactive to user and provide better experience to the user.
   So interface to the final presentation of media is usually interactive.

8) Why operating system is needed in computers? How time sharing operating system works? (3+3)

Ans:

Operating system is needed in computers because of following reasons:

1. To make a computer system convenient to use in an efficient manner.
2. To hide the details of the hardware resources from the users.
3. To provide users a convenient interface to use the computer system.
4. To act as an intermediary between the hardware and its users and making it easier for the users to access and use other resources.
5. To manage the resources of computer  system.
6. To keep track of who is using which resource, granting resource request according for resource using and mediating conflicting requests from different programs and users.
7. To provide efficient and fair sharing of resources among user and programs.

The time sharing system provides the direct access to a large number of users where CPU time is divided among all the users on scheduled basis. The OS allocates a set of time to each user on scheduled basis. The OS allocates a set of time to each user. When this time is expired, it passes control to the next user on the system. The time allowed is extremely small and the users are given the impression that they  each have their own CPU and they are the sole owner of the CPU. This short period of time during that user gets attention of the CPU  is known as a time slice or a quantum.

9) How tables are created in Ms Access and how data are inserted into the tables? (6)

Ans: Not included in syllabus. You can study about by clicking here : create-a-table-and-add-fields

10) What do you mean by hash function? How hash functions can be used in digital signatures? (3+3)

Ans:

A hash function is a mathematical function that converts a numerical input into another compressed numerical value. The input to hash function is of arbitrary length but output is always of fixed length. Values returned by a hash function are called message digest or simply hash values.

There are two direct application of hash function based on its cryptographic properties. They are:

1. Password storage - Hash function provides protection to password storage. Instead of storing password in clear, mostly all logon processes store the hash values of passwords in the file. The password file consists of a table of pairs which are in the form (user id, h(P)).
2. Data Integrity Check - Data integrity check is a most common application of the hash functions. It is used to generate the checksums on data files. This application provides assurance to the user about correctness of the data.

The following process explains how hash functions can be used in digital signatures:

• Each person adopting this scheme has a public private key pair.
• Generally, the key pairs used for encryption/decryption and signing/verifying are different. The private key is used for the signing is referred to as the signature key and the public key as the verification key.
• Signer feeds data to the hash function and generates hash of data.
• Hash value and signature key are then fed to the signature algorithm which produces the digital signature on given hash. Signature is appendage to the data and the both are sent to the verifier.
• Verifier feeds the digital signature and the verification key into the verification algorithm. The verification algorithm gives some value as output.
• Verifier also runs same hash function on received data to generate hash value.
• For verification, this hash value and output of verification algorithm are compared. Based on the comparison result, verifier decides whether the digital signature is valid.
• Since digital signature is created by ‘private’ key of signer and no one else have this key; the signer cannot repudiate signing the data in future.

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