Computer Science 1BA3 Midterm Review
Chapter Two
Representing Digital Data (Page 5558)
Binary Numbering System:
The numbering system that represents all numbers using just two symbols
(0 and 1).
Byte: 8 bits
Kilobyte (KB): 1000 bites
Megabyte (MB): 1 million bytes
Gigabyte (GB): 1 billion bytes
Terabyte (TB): 1 trillion bytes
•
All data must be converted into bits before computer can store or process it
•
As the computer processes only bit operations (as directed by the programs), the
interpretation of a string of bits as numbers, words and other information is done by the
software
ASCII (American Data Standard Code for Information Interchange):
coding system traditionally
used with PCs
Unicode:
A coding system for textbased data using any written language
Unicode is a universal coding system designed to read any written language
•
16bit code providing 65,536 characters and symbols
EBCDIC:
A fixedlength, binary coding system widely used to represent textbased data on IBM
Representing Numbers
1.
We have ASCII codes for digits, so represent numbers as strings of ASCII characters
2.
Text may be practical for representing symbolic data that are number strings such as student I.D.
numbers or phone numbers (arithmetic operations not required)
3.
In general it is not practical to store numeric values
(arithmetic required) as strings of characters
4.
Largest number that can be represented by two bytes using ASCII codes = 99
Place value of decimal number system
The Binary Number System
•
To convert decimal data that humans use, into binary number system.
•
The binary number system works the same way as the decimal system, but has only two available
symbols (0 and 1) rather than ten (0, 1, 2, 3, 4, 5, 6, 7, 8, and 9).
•
A string of bits can be used to represent a subset of integers in several different ways:
If only positive integers are represented the range can be
0 to 65,535
•
If both negative and positive integers (signed integers
) are to be represented:
•
the bit patterns must encode the sign as well as the magnitude of the integers
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There are several methods when using 16 bits, the range of integers 32768 to +32767 can be
represented.
•
Using 32 or 64 bits can increase the range of integers that can be represented
Conversion of Binary to Decimal
Representing Real Numbers (Page 5657)
Graphics Data (Page 5859)
How Are Images Represented?
o
Made up of tiny dots called pixels
o
A pixel: the smallest part of an image; A number representing the colour in the image
o
Image is split up into columns and rows and the pixels take up all of them
o
Example: An image could have 60,000 pixels; if an image is just Black and White, it's called a
binary image.
o
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 Fall '08
 EBRAHIM
 Computer Science, Central processing unit, USB flash drive, Hard disk drive, Floppy disk

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