Notes

Outline

Announcements Project 1b is due Monday Tests are graded, expect them back shortly. (I was pleased with the results.)

Computer Basics How exactly does a computer work?

Integrated Circuits Integrated circuits (ICs) are the power source of the information revolution When computers were made of discrete parts, wires of every transistor (3), capacitor (2), resistor (2), etc. had to be hand-connected Labor intensive, expensive, error prone, unreliable, cumbersome, … Integrated circuits solved that by 2 ideas Integration -- circuits built as a unit from like parts Photolithography -- printing process to make chips

Photolithography Consider process for depositing wires

Remove Resist

Semiconductors Silicon, a semiconductor -- sometimes conducts and sometimes does not When semiconductors do and don’t conduct can be controlled The degree to which semiconductors conduct can be enhanced Ex.: Use control to test Thai AND cuisine

Field Effect Charged objects are familiar -- use a nylon comb on a dry day A charged field can control whether a semiconductor conducts or not The plan The control wire’s charge is the key Neutral control wire, wire does not conduct Charged control wire, implies wires conduct

MOS TRansistors The field effect idea is implemented in metal-oxide-semiconductor transistors

Operation The two cases are, the gate is neutral or the gate is charged

Computers ... Deterministically execute instructions to process information “Deterministically” means that when a computer chooses the next instruction to perform it is required by its construction  to execute a specific instruction based only on the program and input it is given

Fetch/Execute Cycle Computer = instruction execution engine The fetch/execute cycle is the process that executes instructions

Anatomy of a Computer

Memory ... Programs and their data must be in the memory while they are running

Control The Fetch/Execute cycle is hardwired into the computer’s control, i.e. it is the actual “engine”

Indirect Data Reference Instructions tell where the data is, not what the data is … contents change

ALU The Arithmetic/Logic Unit does the actual computation

Input/Output Input units move data from memory to outside world; output units bring data from outside world into memory Most peripheral devices are “dumb” meaning that the processor assists in their operation Disks are memory devices because they can output information and input it back again

The PC’s PC The program counter (PC) tells where the next instruction comes from Instructions are a word long, so add 4 to the PC to find the next instruction

Clocks Run The Engine The rate a computer “spins around” the Fetch/Execute cycle is controlled by it’s clock rate Current clocks run 2-3 GHz In principle, the computer should do one instruction per cycle, but often it fails to Modern processors try to do more than one instruction per cycle, and often succeed