1 COMS 161 Introduction to Computing Title: The Digital Domain Date: September 3, 2004 Lecture Number: 5

2 Announcements Questions Comments Concerns Criticism Jokes

3 Review Analog (continuous) Information Digital information –Advantages –Disadvantages

4 Outline Digital information –Advantages

5 Digital advantages 8.Random Access Direct access to digital data, provided we know where to look for it Random access –All accesses take the same amount of time (latency) regardless of where the data resides

6 Digital advantages 8.Random Access(Cont.) Sequential access –Analog information –Must pass information that comes before what you wish to find 9.Selective Access Searched by content (selective) Find occurrences of a given word in a document

7 Digital advantages 10.Compression Useful information is not totally redundant or totally random Redundant information –Repeating quality Random information –Nothing in common –TV snow –This lecture?

8 Redundant –How many times does this message have to be transmitted, heard, or seen before it is not necessary to continue »COMS 161 is the best of the best classes at the H-S-C

9 Redundant –Redundancy permits data compression Remove some of the redundancy Keep enough –Reconstruct the original exactly –Reconstruct a reasonable approximation of the original Example of compression –Repeat the following phrase eleven times »COMS 161 is the best of the best classes at the H-S-C

10 Random –Can you guess what this picture is?

11 Digital advantages 11.Content Analysis and Synthesis Digital data can be processed, combined, and analyzed Ordered based on content Cookies –Allow web sites to tailor to you 12.Broad usefulness Many different forms of information can be represented this way

12 Digital Domain Analog information –The natural form for many different types of information –Continuous in at least one dimension Digital information –Language of the computer –Analog information must be converted into a discrete (digital) form –Multimedia is all digital information

13 Digital Domain Converting analog to digital information –We need a digital representation of the information –Recall, digital is a discrete system Where symbols are numbers The digital advantages –Therefore, we need a numerical encoding of the data Numerical means numbers

14 Numbers Two types of notion used to represent numbers –Non-positional notation No special significance is given to order –Counting numbers on your fingers –Tick mark counting method »The number of items is important, not the order –My honey do list »Not important which task I do first, just so I get them all done

15 Numbers –Positional notation Significance is given to order the digits appear in the number The decimal numbering system uses positional notation –This is the system we use –365 is not the same a 653 »These are completely different numbers »They use the same digits

16 Positional notation 365 means –Three hundreds –Six tens –Five ones Each digit is multiplied by a power of 10

17 Decimal number system Synonyms –Decimal number system –Decimal notation –Base-10 system Both digits and their location in the number are important Ten unique symbols (digits) –0, 1, 2, …, 9

18 Octal number system Decimal is not the only positional number system available –Octal Positional,base-8 system Each digit is multiplied by a power of 8 Eight unique symbols (digits) –0, 1, 2, …, 7

19 Binary number system –Binary Positional, base-2 system Each digit is multiplied by a power of 2 Two unique symbols (digits), 0 and 1

20 Binary number system Digital and binary relationship –The language of computers use binary digits –Only 2 possible values 0 and 1 –Much simpler to make electronics that distinguish between one of two values Distinguishing between more than two values is very difficult

21 Binary number system Since binary digits have two possible values Binary digits are called bits –They only contain a little “bit” of information –Numbers represented in binary form will (most likely) require more digits (bits) than the decimal form