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Published byMichael O’Neal’ Modified over 9 years ago
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Number Representation
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Representing numbers n Numbers are represented as successive powers of a base, or radix
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Representing numbers n Numbers are represented as successive powers of a base, or radix n The powers increment upwards to the left, starting with zero to the far right
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Representing numbers n Numbers are represented as successive powers of a base, or radix n The powers increment upwards to the left, starting with zero to the far right n For any base, b: b 0 b 1 b 2 b 3 etc....
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Representing numbers n We typically use a base of 10 (presumably because we have ten fingers), the decimal system 10 0 1 2 3 etc.... ones column tens column hundreds column thousands column
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Representing numbers n For any base b, there are b digits
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Representing numbers n For any base b, there are b digits n In base 10, there are 10 digits – 0 through 9
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Representing numbers n For any base b, there are b digits n In base 10, there are 10 digits – 0 through 9 10 0 1 ones column tens column When we want to represent a value greater than the highest digit, we have to make a change in the appropriate column to the left 1234567891708920 etc....
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Representing numbers n In any base b, if we have n digits, the range of values we may represent is b n n If we have two digits in base 10, b=10 and n=2 n With two digits, we can represent 10, or 100, values – 0 through 99 2
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Representing numbers in computers n Computers may store and transmit numbers in the form of circuits
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Representing numbers in computers n Computers may store and transmit numbers in the form of circuits n A circuit has two states: ON and OFF
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Representing numbers in computers n Computers may store and transmit numbers in the form of circuits n A circuit has two states: ON and OFF n Computers are therefore able to represent numbers in a system that has two digits
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Representing numbers in computers n Computers may store and transmit numbers in the form of circuits n A circuit has two states: ON and OFF n Computers are therefore able to represent numbers in a system that has two digits n Base two, the binary system, fits this description
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Representing numbers in computers n Computers may store and transmit numbers in the form of circuits n A circuit has two states: ON and OFF n Computers are therefore able to represent numbers in a system that has two digits n Base two, the binary system, fits this description n The binary number system has the digits 0 and 1
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Binary numbers n Binary numbers have only two digits
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Binary numbers n Binary numbers have only two digits n But that distinction aside, the system of representing numbers is exactly the same as in the decimal system: 2 0 2 1 2 2 2 3 etc.... ones column twos column fours column eights column 2 4 sixteens column
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Binary numbers n With only two digits, a sequence of binary numbers changes columns more quickly than a series of decimal numbers: Decimal Binary 0 0 1 1 2 10 3 11 4 100 5 101 6 110 7 111 8 1000 etc....
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Essential terminology n When a binary number is used by a computer, a single digit is called a bit (short for binary digit) 10110010 bit n Numbers (computer words) are often stored in sequences of eight bits, called a byte byte n A sequence of four bits is called a nibble nibble
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Essential terminology n The bit that represents the lowest power is called the least significant bit 10110010 least significant bit n The bit that represents the highest power is called the most significant bit most significant bit
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Essential terminology n Larger numbers need to be represented with two or more bytes (16 bits form a two-byte word) 10110010 least significant byte n The byte that represents the lower powers of the number is called the least significant byte most significant byte 10110010 n The byte that represents the higher powers of the number is called the most significant byte
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Bit resolution n A computer system is often referred to as an “n bit system,” meaning it represents numbers with n digits
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Bit resolution n A computer system is often referred to as an “n bit system,” meaning it represents numbers with n digits n In a binary system, b=2, so this is a statement to describe the resolution of the system
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Bit resolution n A computer system is often referred to as an “n bit system,” meaning it represents numbers with n digits n In a binary system, b=2, so this is a statement to describe the resolution of the system n An 8-bit system can represent 2, or 256, values 8
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Bit resolution n A computer system is often referred to as an “n-bit system,” meaning it represents numbers with n digits n In a binary system, b=2, so this is a statement to describe the resolution of the system n An 8-bit system can represent 2, or 256, values n A 16-bit system can represent 2, or 65,136 values 8 16
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Hexadecimal notation n Base 16, the hexadecimal system, is often used in computer parlance
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Hexadecimal notation n Base 16, the hexadecimal system, is often used in computer parlance n Since our Arabic number system does not have digits to represent values greater than 9, alphabetic characters are used: DecimalHexadecimal 0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 A 11 B 12 C 13 D 14 E 15 F
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Hexadecimal notation n Hexadecimal notation is a convenience
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Hexadecimal notation n Hexadecimal notation is a convenience n A four-bit nibble can be expressed as one hexadecimal bit
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Hexadecimal notation n Hexadecimal notation is a convenience n A four-bit nibble can be expressed as one hexadecimal bit n An eight-bit byte can be expressed as two hex bits 10100110 A6 To convert to decimal, multiply the most significant nibble by 16, then add the least significant nibble: (10 * 16) + 6 = 166
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