COMS 161 Introduction to Computing

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

Announcements • May miss later part of office hours today and Wednesday

Review • Hexadecimal Numbers • Digitization

Outline • Digitization • Computer System Basics

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

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

Quantizing Images All gray values in each sample are averaged

Quantizing Images Different amount of sampling

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

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

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

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

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

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

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!!!

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

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

3 + 5 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

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

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

Computer Systems • 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 • 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

COMS 161 Introduction to Computing