# Unit 3 Data Representation

Jarrow School
19 de Oct de 2016
1 de 14

### Unit 3 Data Representation

• 1. Unit 3 – Data representation
• 2. 65 Denary to Binary Start by writing out the place values. 1248163264128 Then write 1s underneath the place values that add up to the denary number. 0 1 0 0 0 0 0 1
• 3. 64 16 1+ + = 81 Binary to Denary 0 1 0 1 0 0 0 1 Start by writing the place values above each bit. 1248163264128 Then write out the place values of the 1s. Finally add the numbers together.
• 4. Binary Addition The process of performing addition in binary is very similar to addition in denary. 1 1 1 1 0 1 1 0 1 0 0 1 1 1 + 1 0 1 0 0 Rules: 0 + 0 = 0 0 + 1 = 1 1 + 1 = 0 carry 1 1 + 1 + 1 = 1 carry 1 0 1 1 0 0 1 0 1 1 1 + 1 1 1 0 0 1 0 1 0 1 +
• 5. Overflow When there isn’t enough room for a result, this is called an overflow and it produces an overflow error. 1 1 1 1 1 1 1 0 1 1 1 0 1 1 1 + 1 1 0 1 0 0 No room for a carry, so it is lost and we get the wrong answer. Humans can easily work around this, but it isn’t so easy for a computer.
• 6. Binary Subtraction The process of performing subtraction in binary is very similar to subtraction in denary. 1 1 0 0 0 1 0 0 - 1 0 0 0 Rule: 0 - 1 won’t go so borrow 10 (2) from the column to the left. 2 - 1 = 1. 10 10 1 1 0 1 0 1 1 1 - 0 1 1 0 1 1 1 0 0 1 0 1 -
• 7. Sign and Magnitude This is the simplest method of representing negative numbers in binary. The most significant bit is the ‘sign bit’. Sign bit 128 64 32 16 8 4 2 1 0 0 0 0 1 1 0 1 1 +27 1 0 0 0 1 1 0 1 1 -27 1 = minus 0 = plus
• 8. The Problem with Sign and Magnitude The problem with sign and magnitude is that addition doesn’t always work. 0 0 0 0 0 1 1 1 (+7) 1 0 0 0 0 1 0 1 (-5) + 1 0 0 0 1 1 0 0 (-12)
• 9. Two’s Complement Two’s complement is an alternative method of representing negative numbers. This method works with binary addition. The most significant bit is a minus number. -128 64 32 16 8 4 2 1 1 0 0 0 1 1 0 1 -128 + 8 + 4 + 1 = -115
• 10. Floating Point Numbers In binary floating point numbers are split into two parts; the Mantissa and the Exponent. Mantissa Exponent 0111 1000 0000 0011 0 . 1 1 1 1 0 0 0 The mantissa contains the actual number and the exponent defines the position of the binary point.
• 11. Floating Point Numbers The numbers to the right of the binary point define the fraction. 0 1 1 1 . 1 0 0 0 In denary the number above is: 7 ½ 1/2 1/4 1/8 1/16 8/16 4/16 2/16 1/16
• 12. Hexadecimal Programmers often use hexadecimal numbers as a shorthand for binary to save time. Hexadecimal (hex) numbers are based on the number 16. Each column has a value 16 times that of the one on its right. place value 256 16 1 There are 16 different values available in hex: Letters are used for values 10-15 to ensure that only single digits are used. 0 1 2 3 4 5 6 7 8 9 A B C D E F
• 13. Hexadecimal to Binary Converting between hexadecimal and binary is particularly easy. You just take each character and convert it into the equivalent binary number. Hex D B Denary 13 11 Binary 1 1 0 1 1 0 1 1 In this example we will convert DB hex to binary.
• 14. Binary to Hexadecimal You convert between binary and hexadecimal by doing the reverse. You just take each group of four binary digits, starting from the right and convert it into the equivalent hex number. Binary 1 1 1 1 0 0 1 1 Hex F 3 In this example we will convert 11110011 to hexadecimal: