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Ch. 3 Number and Character Coding Systems - Coggle Diagram
Ch. 3 Number and Character Coding Systems
Number System
Denary number system
Hexadecimal number system
Binary number system
Number Representation in Computer Systems
Byte
A data unit used in computers
Consists of 8 bits and is the smallest addressable unit in a
microprocessor.
Word
Modern computers can handle data stored in two or more bytes at a time.
The natural unit of data used by a computer is called a word.
The word length(word size) is measured in bits.
Modern computers usually have a word length of 16, 32 or 64 bits.
Bit
A single digit
The base unit for storing data in a computer
A single bit can only represent two distinct values.
For example: 0 or 1, True or False, On or Off
An n-bit binary number can represent 2^n distinct values
Addition and Subtraction of Different Number Representations
The calculation on both addition and subtraction of unsigned in other number
systems is the same as that in the denary system.
A ‘ carry ’ is generated when the sum of digits equals or exceeds the base value.
A ‘ borrow’ from the left digit is necessary if a larger digit is subtracted from a smaller
one.
Overflow Error
Occur when the calculation result is outside the range that the digits can
represent.
Character Coding Systems
Other than numeric data, a computer needs to store and process characters.
The character coding system is a way to represent characters in a form that can be
manipulated efficiently in a computer.
ASCII
American Standard Code for Information Interchange (ASCII)
Each ASCII character consists of 7 bits and it can contain 2^7 (i.e. 128) different characters
Standard ASCII: 128 characters
Extended ASCII: 256 characters
Chinese characters are usually represented in:
Big 5 code : traditional Chinese
Guo Biao (GB) code: simplified Chinese
Unicode
Used to represent all the existing languages in the world
Contain about 100,100 characters
The representations of Unicode known as code points are variable in length.
Made up of one to four bytes
The code points are carefully defined so that the most frequently used characters, such as the ASCII, are put at the front of the code table.
These characters can be represented by a one-byte code point.
Extended Binary-Coded Decimal Interchange Code (EBDIC)
Each code represents either a printable character or a non-printable character (e.g. end-of-line character)