Page 1 : Computer Science - XI, , Chapter 2: Data Representation and Boolean Algebra, Base of a number system: The number of symbols used in a number system is called base or, radix of a number system, MSD and LSD: Left most digit of a number is MSD and right most digit of a number is LSD., Different Number Systems:, , Number Conversion procedure:, , Number representation methods: (i) Sign and magnitude representation (ii) 1’s complement, representation (iii) 2’s complement representation., ASCII: American Standard Code for Information Interchange. It uses 7 bits to represent a, character in computer memory. It can represent only128 characters. Another version is, ASCII-8 uses 8 bits for each character, can represent 256 different characters., EBCDIC: Extended Binary Coded Decimal Interchange Code. This is similar to ASCII and is an, 8 bit code. It can represent 256 characters., , 1, , Joy John’s CS Capsule

Page 2 : Computer Science - XI, ISCII: Indian Standard Code for Information Interchange or Indian Script Code for, Information Interchange. It uses 8-bits and can represent various writing systems of India., Unicode: Originally used 16 bits which can represent up to 65,536 characters. Nowadays, Unicode uses more than 16 bits and hence it can represent more characters. Unicode can, represent characters in almost all written languages of the world., Boolean operations: The operations performed on the Boolean values 0s and 1s. The, operations are OR (Logical Addition), AND (Logical Multiplication), NOT (Logical Negation)., Logic gate: It is a physical device that can perform logical operations on one or more logical, inputs and produce a single logical output., Truth Table: It is a table that shows Boolean operations and their results., OR operation & Gate, , AND Operation & Gate, , NOT Operation & Gate, , Boolean Laws:, , De Morgan’s theorems:, , Universal Gates: The NAND and NOR gates are called universal gates. A universal gate is a, gate which can implement any Boolean function without using any other gate type., NAND: It is an inverted AND operation. NAND gate is an inverted AND gate., 2, , Joy John’s CS Capsule

Page 3 : Computer Science - XI, NOR: It is an inverted OR operation. NOR gate is an inverted OR gate., , NAND operation and NAND gate, , NOR operation and NOR gate, , AND using NAND:, , OR using NAND:, , OR using NOR:, , AND using NOR:, , NOT using NAND and NOR:, , 3, , Joy John’s CS Capsule

Page 4 : Computer Science - XI, , Questions from Previous Years’ Question Papers, 1. NAND gate is known as universal gate because it can be connected to other NAND gates, to generate any logic function. Show how will you connect NAND gates to produce OR, gate, AND gate and inverter., (3) (July 2017), 2. Represent the following integers in sign and magnitude form, 1’s complement from and, 2’s complement form by using eight bits., a) +25, b) –30, (3) (July 2017), 3. Briefly explain any three methods of representing characters in computer memory., (3) (July 2017), 4. The number (158)10 can be represented in Hexadecimal number system as ……….., (1) (March 2017), 5. Represent –38 in 2’s complement form., , (2) (March 2017), , 6. Draw the logic circuit for the Boolean expression:, (A+ BC )+ AB, , (3) (March 2017), , 7. Using algebraic method, prove that Y . Z + Y . Z+Y .Z + Y = 1, , (3) (March 2017), , 8. Which one of the following file extensions is different from others?, a) WAV, b) MP3, c) PNG, d) MIDI, (1) (Sept. 2016), 9. Perform the following number conversions:, a) (110111011.11011)2 = ( ………… )8, b) (128.25)10 = ( ………… )8, , (2) (Sept. 2016), , 10. With the help of a neat circuit diagram, prove that NAND gate is a universal gate., (2) (Sept. 2016), 11. 1’s compliment of the binary number 110111 is ______. (Hint: Use 8 bit form), (1) (March 2016), 12. Express the integer number –39 in sign & magnitude representation. (2) (March 2016), 13. Following are the numbers in various number systems. Two of the numbers are same., Identify them:, (a) (310)8, , (b) (1010010)2, , (c) (C8)16, , (d) (201)10, , (3) (March 2016), , 14. Consider the following Boolean expression: (Bl+A)l = B. Al, Identify the law behind the above expression and prove it using algebraic method., (3) (March 2016), 15. Computers use a fixed number of bits to represent data which could be a number, a, character, image, sound, video etc. Explain the various methods used to represent, characters in memory., (3) (Sept. 2015), 16. Draw the logic circuit for the function:, (3) (Sept. 2015), 17. Prove algebraically: x.(y.z) = x.y + x.z, , (3) (Sept. 2015), 4, , Joy John’s CS Capsule

Page 5 : Computer Science - XI, 18. Fill in the blanks:, (a) (0.625)10 = ( _______ )2, (b) (380)10, , = ( _______ )16, , (c) (437)8, , = ( _______ )2, , (3) (March 2015), , 19. What do you mean by universal gates? Which gates are called universal gates? Draw, their symbols., (3) (March 2015), 20. Construct a logical circuit for the Boolean expression a . b + a . b . Also write the truth, table., (3) (March 2015), , 5, , Joy John’s CS Capsule