Data
(資料) Text
(文字) Number
(數字) Image
(影像) Audio
(音訊) Video
(視訊) Numbers, text, images, audio, and video are all forms
of data. Computers need to process all types of data.
Multimedia
The computer industry uses the term
“multimedia” (多媒體) to define
Information that contains numbers,
text, images, audio, and video.
2.2
Data Inside
The Computer
(電腦裡的資料)
Bit Pattern (位元樣式)
All data types from outside a computer are transformed into a uniform(一致的) representation(表示) called a bit pattern for processing by computers.
A bit is the smallest unit of data that can be stored in a computer
Bit Pattern (位元樣式)
1 byte = 8 bits 1 KB = 1024 bytes 1 MB = 1024 KB 2 bytes = 16 bits 1 GB = 1024 MB K : kilo (千)
M: mega (百萬)
G: giga (十億) 210 = 1024 A bit pattern of length 8 is called a byte
Byte also been used to measure(測量) the size of memory or other storage devices
Bit Pattern (位元樣式)
1000101010111111 A switch, with its two states of on and off, can represent a bit(0 or 1)
A bit pattern is a sequence of bits that can represent a symbol
Examples of Bit Patterns
Data are coded (邊碼) when they enter a computer and decoded (解碼) when they are presented to the user
2.3
Representing Data
(表達資料)
Representing Symbols Using Bit Patterns (用位元樣式來表達符號)
How many bits are needed in a bit pattern to represent a symbol in a language?
Depend on how many symbols are in the set (集合)
Number of Symbols and Bit Pattern Length (符號數量與位元長度)
Number of Symbols ---------------------
2
4
8
16
…
128
256
…
65,536 Bit Pattern Length ---------------------
1
2
3
4
…
7
8
…
16
Codes (編碼法)
Code: different sets of bit patterns have been designed to represent text symbols
ASCII: popular code for symbols
EBCDIC: used in IBM mainframes (IBM大型主機)
Unicode (萬國碼): 16-bit code, allow a greater number of symbols
ISO: 32-bit code, allow a greater number of symbols
Coding (編碼)
Coding is the process of transforming data into a bit pattern
ASCII
27 = 128 American Standard Code for Information Interchange (美國資訊交換標準碼)
The code be developed from the American National Standards Institute (ANSI, 美國國家標準局)
ASCII uses 7 bits for each symbol
Some Features of ASCII
ASCII uses a 7-bit pattern: 0000000 ~ 1111111
0000000 null character (空字元); 1111111 delete character (刪除字元)
There are 31 control (nonprintable，無法印出的) characters
The numeric (數字) characters (0~9) are coded before letters (字母)
Some Features of ASCII
There are several special printable (可列印出的) characters
The uppercase letters (A~Z) come before the lowercase letters (a~z)
The upper and lowercase characters are distinguished by only 1 bit. (A 1000001; a 1100001)
There are six special characters between the upper and lowercase letters
Extended ASCII (擴充的 ASCII)
To make the size of each pattern 1 byte (8 bits), the ASCII bit patterns are augmented with an extra 0 at the left.
Extended ASCII uses a 8-bit pattern: 00000000 ~ 01111111
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