1. 1 COMS 161 Introduction to Computing Title: Computing Basics Date: September 13, 2004 Lecture Number: 9

2. 2 Announcements May miss later part of office hours today and Wednesday

3. 3 Review Hexadecimal Numbers Digitization

4. 4 Outline Digitization Computer System Basics

5. 5 Images are digitized using a two step process Sampling the continuous tone image Quantizing the samples Digitizing Images

6. 6 Sample image by pixel resolution Spatial Sampling Sample two- dimensional space Sampling Images

7. 7 All gray values in each sample are averaged Quantizing Images

8. 8 Different amount of sampling Quantizing Images

9. 9 Different amount of sampling Quantizing Images

10. 10 Different amount of sampling Quantizing Images

11. 11 Computer Systems A dime a dozen!! –They are everywhere and their uses continue to expand Microwaves Clocks Cars Watches What’s next –Shoes??

12. 12 Computer System Electronic digital data processing machines –Data: symbolic representation of information –Digital: numeric codes –Computers are discrete state machines Finite number of states –All are distinct and different Always in a state

13. 13 Computer System Programs, Applications, or Process –Set of actions –Traversing certain states Sequence of distinct states –Fast to go from one state to another Billionths of a second –So fast, a process appears continuous As do light bulbs Your TV screen

14. 14 Computer System Mechanical computers Mechanical and electrical Electromechanical Electronic –Fastest, but still performs simple steps –One of the great illusion of the computer: Lots of simple steps performed quickly enough make the computer appear complicated

15. 15 Computer Systems Evolution State transitions are simple –Baby steps –States are independent Does not matter on state before or after Instructions cause state transitions –Going from one state to the next –Must be precise and unambiguous Causing the desired state transition –Instructions are executed

16. 16 DWIM The notorious instruction –Prof P’s grand challenge $1000.00 reward –Make a machine the executes the DWIM instruction Do What I Mean

17. 17 Computer Systems Unlike students (and my daughters) –Computers do what they are told to do Nothing more, nothing less Computer Programs (applications) –Consist of a sequence of instructions –Running a program Executing one instruction after another –This is the primary job of the computer!!!

18. 18 Computer Systems Think of the computer as a dogg! –Here boy, here boy, … –Fetch-decode-execute cycle –No good boy or treats are necessary!! Fetch the next instruction Decode the instruction Execute the instruction Repeat

19. 19 Computer Systems The fetch-execute cycle –This is not your fathers Orange County Chopper!!

20. 20 Computer Systems Data instructions –Instructions that perform an operation on specified data add 3, 5 Instruction refers to the values to be added directly –Instruction has direct access to the values to be added 3 5 +

21. 21 Computer Systems Indirection –Advantageous to refer to data indirectly Makes programs more general –Instruction tells where the data is, not what the data is Other values can be stored and processed –add val1, val2 val1 and val2 refer to locations that contain the values to add

22. 22 Indirection Computer Systems 3 7 12 1 5 234 2 3 45 135 5 + val1 val2 val1 and val2 could refer to any other place which contains other values

23. 23 Instructions that refer to data –Put the values in special places Get the values from where they are Save them in a place where the adder looks for its input –Execute the add instruction –Place the result someplace Computer Systems

24. 24 Computer Systems Slight variant of the add instruction add val1, val2, val3 –Fetch the values (operands) to be added Read the memory at the location of val2 Put the value on one of the adder inputs Read the memory at the location of val3 Put the value on the other adder inputs –Execute the add –Put result in memory at location val1