Chapter 2 Binary Values and Number Systems

2 624 Chapter Goals Distinguish among categories of numbers Describe positional notation Convert numbers in other bases to base 10 Convert base-10 numbers to numbers in other bases Describe the relationship between bases 2, 8, and 16 Explain the importance to computing of bases that are powers of 2

3 2 Natural numbers, a.k.a. positive integers Zero and any number obtained by repeatedly adding one to it. Examples: 100, 0, 45645, 32 Negative numbers A value less than 0, with a – sign Examples: -24, -1, , -32 Numbers

4 3 Integers A natural number, a negative number, zero Examples: 249, 0, , - 32 Rational numbers An integer or the quotient of two integers Examples: -249, -1, 0, 3/7, -2/5 Real numbers In general cannot be represented as the quotient of any two integers. They have an infinite # of fractional digits. Example: Pi = …

5 4 How many ones (units) are there in 642? ? Or is it ? Or maybe… ? Natural Numbers

6 5 Aha! 642 is in BASE 10 The base of a number determines the number of digits and the value of digit positions Natural Numbers

7 6 Continuing with our example… 642 in base 10 positional notation is: 6 x 10 2 = 6 x 100 = x 10 1 = 4 x 10 = x 10º = 2 x 1 = 2 = 642 in base 10 This number is in base 10 The power indicates the position of the number Positional Notation

8 7 d n * R n-1 + d n-1 * R n d 2 * R + d 1 As a formula: 642 is 6 3 * * R is the base of the number n is the number of digits in the number d is the digit in the i th position in the number Positional Notation

9 68 What if 642 has the base of 13? 642 in base 13 is equal to 1068 in base = x 13 2 = 6 x 169 = x 13 1 = 4 x 13 = x 13º = 2 x 1 = 2 = 1068 in base 10 Positional Notation

10 9 Decimal is base 10 and has 10 digits: 0,1,2,3,4,5,6,7,8,9 Binary is base 2 and has 2 digits: 0,1 In a given base R, the digits range from 0 up to R-1 R itself cannot be a digit! (in base R) Why? The question is “How many digits?” “Off by one” error Binary

Practice binary numbers: = ??? 10 11

There are only 10 kinds of people: those who understand binary and those who don’t 12

13 7 d n * R n-1 + d n-1 * R n d 2 * R + d 1 In CS, binary digits are numbered from zero, to match the power of the base: Positional Notation revisited d n-1 * R n-1 + d n-2 * R n d 1 * R 1 + d 0 * R 0 d n-1 * 2 n-1 + d n-2 * 2 n d 1 * d 0 * 2 0 Bit zeroBit oneBit n-1

14 10 How are digits in bases higher than 10 represented? With distinct symbols for 10 and above. Base 16 (hexadecimal, a.k.a. hex) has 16 digits: 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E, and F Bases Higher than 10

Practice hex numbers: 2AF 16 = ??? 10 15

16 What is the decimal equivalent of the octal number 642? = ??? Converting Octal to Decimal

17 What is the decimal equivalent of the octal number 642? 6 x 8 2 = 6 x 64 = x 8 1 = 4 x 8 = x 8º = 2 x 1 = 2 = 418 in base Converting Octal to Decimal

18 What is the decimal equivalent of the hexadecimal number DEF? DEF 16 = ??? 10 Converting Hexadecimal to Decimal

19 What is the decimal equivalent of the hexadecimal number DEF? D x 16 2 = 13 x 256 = E x 16 1 = 14 x 16 = F x 16º = 15 x 1 = 15 = 3567 in base 10 Remember, the digits in base 16 are 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F Converting Hexadecimal to Decimal

20 What is the decimal equivalent of the binary number ? = ??? Converting Binary to Decimal

21 What is the decimal equivalent of the binary number ? 1 x 2 6 = 1 x 64 = x 2 5 = 1 x 32 = x 2 4 = 0 x 16 = x 2 3 = 1 x 8 = x 2 2 = 1 x 4 = x 2 1 = 1 x 2 = x 2º = 0 x 1 = 0 = 110 in base Converting Binary to Decimal

Are there any non-positional number systems? Hint: Why did the Roman civilization have no contributions to mathematics? 22

See you in the lab! 23

24 Remember that there are only 2 digits in binary, 0 and is 0 with a carry Carry Values Addition in Binary

25 Practice addition: Carry values go here Addition in Binary Check in base ten!

26 Remember borrowing? Apply that concept here: Subtracting Binary Numbers Borrow values Check in base ten!

27 Practice subtraction: Subtracting Binary Numbers Borrow values Check in base ten!

28 While (the quotient is not zero) Divide the decimal number by the new base Make the remainder the next digit to the left in the answer Replace the original decimal number with the quotient Algorithm for converting number in base 10 to other bases, a.k.a. repeated division (by the base): 19 Converting Decimal to Other Bases

29 Example: Convert to binary 179  2 = 89 rem. 1  2 = 44 rem. 1  2 = 22 rem. 0  2 = 11 rem. 0  2 = 5 rem. 1  2 = 2 rem. 1  2 = 1 rem =  2 = 0 rem. 1 Notes: The first bit obtained is the rightmost (a.k.a. LSB) The algorithm stops when the quotient (not the remainder!) becomes zero 19 Converting Decimal to Binary LSBMSB

30 Practice: Convert to binary 42  2 = rem = 2 19 Converting Decimal to Binary

31 Converting Decimal to Octal What is 1988 (base 10) in base 8? Try it!

32 Converting Decimal to Octal Answer is :

33 What is 3567 (base 10) in base 16? Try it! 20 Converting Decimal to Hexadecimal

D E F 21 Converting Decimal to Hexadecimal

35 Counting in Binary/Octal/Decimal

36 On a new page in your notebook: Count from 0 to 30 in decimal Add the binary column Add the octal column Add the hex column Add the “base 5” (quinary) column

37 Mark groups of three (from right) Convert each group is 253 in base 8 17 Converting Binary to Octal

38 Mark groups of four (from right) Convert each group A B is AB in base Converting Binary to Hexadecimal

39 End-of-chapter ex. 25: Explain how base 8 and base 16 are related A B 253 in base 8 = AB in base Converting Octal to Hexadecimal

40 Converting with calculators Use these only to check your results! In the homework and exams you have to show all the work for credit! eal/Calculators/BaseConv_calc_1.htm The Windows calculator

41 Computers have storage units called binary digits or bits Low Voltage = 0 High Voltage = 1 all bits have 0 or 1 22 Binary Numbers and Computers

42 Byte 8 bits The number of bits in a word determines the word length of the computer, but it is usually a multiple of 8 32-bit machines 64-bit machines etc. 23 Binary and Computers

43 Ethical Issues Homeland Security How does the Patriot Act affect you? your sister, the librarian? your brother, the CEO of an ISP? What is Carnivore? Against whom is Carnivore used? Has the status of the Patriot Act changed in the last year?

44 Who am I? Can you tell the person sitting next to you three things about me?

45 Do you know? What concept makes positional notation possible? What three sets can children identify? What words represent the third set? How does an abacus work? How does bi-quinary work?

Individual work To do by next class (Wednesday): Read the entire Ch.2 Read the bio of Grace Murray Hopper (p.44) and Ethical issues (p.46) and take 1 page of notes in your notebook (total) Answer end-of-chapter questions 1 – 20 and in your notebook 46

Homework Due next Friday, Sept. 11: End-of-chapter exercises 21, 23, 26, 28, 29, 33, 35, 38 There is a file on the webpage with all the work assigned (individual work + homework) No class this Monday – university is closed for Labor Day! 47