Transcript COMS 161
COMS 161 Introduction to Computing Title: The Digital Domain Date: September 3, 2004 Lecture Number: 5 1 Announcements • • • • • Questions Comments Concerns Criticism Jokes 2 Review • Analog (continuous) Information • Digital information – Advantages – Disadvantages 3 Outline • Digital information – Advantages 4 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 5 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 6 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? 7 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 COMS 161 is the best of the best classes at the H-S-C COMS 161 is the best of the best classes at the H-S-C COMS 161 is the best of the best classes at the H-S-C COMS 161 is the best of the best classes at the H-S-C COMS 161 is the best of the best classes at the H-S-C COMS 161 is the best of the best classes at the H-S-C COMS 161 is the best of the best classes at the H-S-C COMS 161 is the best of the best classes at the H-S-C COMS 161 is the best of the best classes at the H-S-C 8 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 9 Random –Can you guess what this picture is? 10 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 11 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 12 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 13 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 14 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 15 Positional notation • 365 means – Three hundreds – Six tens – Five ones 365 3*100 6 *10 5 *1 2 1 0 3 *10 6 *10 5 *10 • Each digit is multiplied by a power of 10 16 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 17 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 3658 3 * 8 6 * 8 5 * 8 192 48 5 24510 2 1 0 18 Binary number system –Binary • Positional, base-2 system • Each digit is multiplied by a power of 2 • Two unique symbols (digits), 0 and 1 101101 1* 2 0 * 2 1* 2 1* 2 0 * 2 1* 2 5 4 3 2 1 0 1011012 1* 32 0 *16 1*8 1* 4 0 * 2 1*1 1011012 32 8 4 1 4510 19 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 20 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 4510 1011012 21