CSC 110 – Intro to Computing Lecture 8: Computing Components

Announcements Course slides are available from web page  Posted both before and after class  Slides after class includes my drawings Homework #2 due by 5PM today  Solution will be posted tonight  Quiz #2 will be on Tuesday CSC tutors are still available  Hours posted outside Wehle 206 & 208

Service Learning Reminder Get your site selection site form in to me last week (or as soon as possible) Remember to write an experience page each time you volunteer  Web page documenting what you did, what you learned, how you felt  Should help you write end report First set of experience pages due Feb. 23

There’s Something About Adders… Understand what these circuits do:  Half-adder add two bits  Full-adder adds two bits and any carry from the previous digit Know when to use each of the circuits:  Half-adder adds rightmost (least significant) bit  Full-adder adds all other bits, since a 1 may be carried into it

There’s Something About Adders… Be able to combine circuits to add multi- digit binary numbers:  Use carry-out from one adder as the carry-in for the next adder  Use half-adder to add least significant bit; full- adder everywhere else Do NOT memorize the gates in each  I will not ask you to draw this from memory  If you need it after this course, you can always look it up

Half-Adders Adds two input bits  Outputs result bit and carry bit  Cannot be used if there could be a carry-in bit So used to add least significant (rightmost) bit Very important circuit in computers  Addition is very common  Half-adder is found in every computer, calculator, digital watch…

Half-Adder Only this circuit is a Half-Adder  Other circuits may be equivalent, however Result Carry

Half-Adder How to know a circuit is equivalent to half- adder  Circuit is equivalent to a half-adder if both truth tables have identical output  Equivalence can be found in two ways: Memorizing the half-adder circuit and its truth table Memorizing the half-adder circuit and its truth table  Checking that the output matches the result of adding the input together 

Full-Adders Full-adder adds two input bits and the carry bit from the previous  Outputs result bit and another carry bit Needed to add all but least significant bit  Do not know when designing a processor everyplace we will ever carry a 1

Full-Adder More complex than a half-adder because we need to include the carry bit Result

How Does a Computer Work? Discussions usually begin with processor  More formally called the CPU or Central Processing Unit  Examples include: Pentium IV, PowerPC, Itanium, Pentium M…

CPU Design Processor includes many parts  Calculate mathematical & logical functions  Direct actions in rest of computer  Storing small amount of VERY fast memory

How a Computer Is Organized

Connecting the Computer

Arithmetic/Logical Unit Calculates mathematical & logical actions  Adds, subtracts, multiplies, divides, ANDs, ORs, NOTs, NORs… Uses only simply instructions which take one or two inputs a + b/c is two instructions: division and addition  Uses “registers”: VERY fast memory Run at speed of processor Only registers available on a machine

“Input Units” Input Unit A device through which data and programs from the outside world are entered into the computer

“Output Units” Output unit A device through which results stored in the computer memory are made available to the outside world

Storage Devices Still need someway of remembering information  Secondary storage devices used to read/write information

Memory Hierarchy Time required changes depending on where you access memory  Registers: Drive 1 mile  RAM: Drive to Detroit (214 miles)  Hard Drive: Drive to Moon and back (twice!)  CD Rom: Drive to Sun and back Where something stored has slight impact

What’s New in Processors Lots of really interesting work going on  Have names like “Dynamic Branch Prediction” or “Register Renaming Windows”  Actually much more interesting than it sounds First ongoing revolution we will discuss  Most processors are 32-bit, …  … but newest processors are 64-bit

Why Bits Matter 1 bit captures 2 states: 0 or 1 2 bits captures 4 states: 00, 01, 10, 11 3 bits capture 8 states: 000, 001, 010, 011, 100, 101, 110, bits captures 16 states: 0000, 0001, 0010, 0011, 0100, 0101, 0110, 0111, 1000, 1001, 1010, 1011, 1100, 1101, 1110, 1111

Binary Representation Each time we add a bit, we increase the number of states by a multiple of ____ How many different states can n bits represent? This is important because more states means more colors, more pixels, ability to process more money…

Sizes in Perspective 8 bits = 1 byte  4 bits = 1 nibble 1 GB = 1,073,741,824 bytes 1 TB = 1,099,511,627,776 bytes Federal debt (as of Feb. 3 rd ) $8,195,544,127, Largest database 549,755,813,888,000 bytes 1 PB = 1,125,899,906,842,624 bytes

Hard Drive Sizes in Perspective Problem with simplicity: MARKETING  Normally sizes are powers-of-two, but…  Hard drives sizes measured in powers-of-ten SizeActual SizeHard Drive Size 1 KB1024 bytes 1 MB1,048,576 bytes1,000,000 bytes 1 GB1,073,741,824 bytes1,000,000,000 bytes 60 GB64,424,509,440 bytes60,000,000,000 bytes 400 GB429,496,729,600 bytes400,000,000,000 bytes

Control Unit Organizes and directs program execution  Uses several special registers: Instruction Register (IR) holds instruction to execute Program Counter (PC) states instruction to execute next  Control unit insures program executes step- by-step in logical, orderly manner Often to the chagrin of people writing and using the program

von Neumann Architecture Prevalent in all computers today  Store data and instructions together  Uses control unit to drive entire machine  Assumes existence of input & output devices

von Neumann Computer Connections

Harvard Architecture Early “competitor” to von Neumann’s idea  Keep data and instructions in completely different areas  Uses separate controllers to handle programs (instructions) and everything else  Now used only in DSPs and other specialized data-intensive systems

Harvard Computer Connections Program Data

Memory Modern desktop machines are 32-bit  Means they access memory 32-bits at a time  How computers view memory contents:

Memory What does the data represent?  Could be a program, picture, mp3, CSC110 grades, …  Processor translates this data into something more meaningful  Output units then present this information

For next lecture Study for the quiz! Finish reading Section 5 Be ready to finish discussing:  Computer components