fluency with information technology 2012-04-25katherine deibel, fluency in information technology 1...

An Architecture LessonConstructing the CPU

Fluency with Information Technology

2012-04-25 Katherine Deibel, Fluency in Information Technology 1

INFO100 and CSE100

Katherine Deibel

Computer History

Abacus: Fingers, strings, and stones Antikythera mechanism:

Greek mechanical astronomical tool Babbage Difference Engine:

Geared mechanical calculator Vacuum tube computers:

Colossus, Eniac, Univac Transistor Computers:

Manually-wired transistors Integrated Circuits:

Modern age computers


Integrated Circuits

Integrated circuits (ICs) powered the information revolution

When computers were made of discrete parts, millions of hand connections 3 wires per transistor

2 per capacitor

2 per resistor Labor intensive, expensive, error prone,

unreliable, cumbersome, … even with robot manufacturing!


Integrated Circuits

Integrated circuits (ICs) solved that by two ideas Integration:

Circuits built as a unit from alike parts Photolithography:

Printing process to make chips


Jack Kilby

Inventor of the integrated circuitand the handheld calculator

2000 Nobel Prize for Physics First integrated circuit:


Intel Core i7 Processor

758 million transistors (2008)


Photolithography


substrate

oxide

1. Prepare wafer

substrate

oxide

2. Add photoresist

photoresist

Photolithography


substrate

oxide

3. Align photomask 4. Expose to UV light

photoresist

glass

chrome chrome

substrate

oxide

PR

glass

chrome chrome

Photolithography


substrate

oxide

5. Develop and removephotoresist exposedto UV light

6. Etch exposed oxide

substrate

PRPR PRPR

oxide oxide

Photolithography

We now have our circuit board


substrate

7. Remove remainingphotoresist

oxide oxide

The Gist of Photolithography

Think bookmaking Used to be monks copying each page by hand

Printing press requires initial typesetting and then multiple copies are easy

Same idea with integrated circuits Used to require wiring of individual transistors

Create the photomask and the circuit can be created again and again


Semiconductors

Semiconductor: Sometimes it conducts

Sometimes it doesn’t One can control when semiconductors

do and don’t conduct That is the basis for PandA with silicon


Semiconductors

Example: an AND gate

True only if both inputs are true

Send “yes” signal on wire

Make semiconductor conduct if input 1 is true

Detect presence / absence of “yes”

Make semiconductorconduct if input 2 is true


Field Effect

A charged field can control whether a semiconductor conducts or not

A transistor has three wires Source (input)

Drain (output)

Gate (control) The charge of the control wire (gate) is key

Neutral gate, channel doesn’t conduct

Charged gate, channel conducts

In Out

Gate


Computers ...

Deterministically execute instructions to process information Chooses the next instruction as it is

programmed

Executes specific instructions based only on the program and input it is given


Fetch/Execute Cycle

A computer is an instruction execution engine

The fetch/execute cycle is the process that executes instructions

Instruction Fetch (IF)Instruction Decode (ID)Data Fetch (DF)Instruction Execution (EX)Result Return (RR)


Animation

Fetch/Execute cycle

http://courses.washington.edu/fit100/sp12/videos/fetch-execute.swf






Anatomy of a Computer

Memory

ALU Control Input

Floppy Disk

Hard Disk

ScannerKeyboardMouse

OutputSpeakersPrinterMonitor


Memory

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

0

G

1

o

2

D

3

a

4

w

5

g

6

s

7

!

8

!

9

0

10

...

11

byte = 8 bits

0 1 0 0 0 1 0 0

memory addresses

memory contents


Control

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

Instruction: ADDB 20, 10, 16

Put in memory location 20 the contents of memory location 10 + contents of memory location 16

6

10

11

12

13

14

15

12

16 17 18 19

Zz

20

...

21

6

10

11

12

13

14

15

12

16 17 18 19

18

20

...

21


Memory: Words

Memory not usually broken up byte by byte Many data types are longer than one byte

Integers are usually four bytes

Doubles (real numbers) are eight bytes A word is a chunk of several bytes

32-bit machine → 4 bytes per word

Integers are one word

Doubles are two words


Indirect Data Reference

Instructions tell where the data is, not what the data is

An instruction might produce different values even if the command is the same

8

10

11

12

13

14

15

7

16 17 18 19

15

20

...

21

60

10

11

12

13

14

15

-55

16 17 18 19

5

20

...

21

Instruction: ADDB 20, 10, 16


ALU (Arithmetic Logic Unit)

The Arithmetic/Logic Unit does the actual computation

Most computers have only about a 100-150 instructions hard wired

Each type of data has its own separate instructions

ADDB : add bytesADDH : add half wordsADD : add wordsADDS : add short decimal numbersADDD : add long decimal numbersADDBU: add bytes unsigned…


Input/Output

Input units bring data to memory from outside world;

Output units send data to outside world from memory

Most peripheral devices are “dumb” in that the processor assists their operation

Disks are both memory devices and input/output devices


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 (on a 32-bit machine)

110

111

112

113

114

115 116 117 118 119 120

...

121

ADD 210,216,220 AND 414,418,720

Program Counter: 112Program Counter: 112

OR688,724


Clocks Run The Engine

The rate a computer performs the Fetch / Execute cycle is controlled by its clock Current clocks run 2-3 GHz (2-3 trillion cycles a

second!) In principle, one instruction per cycle

Not always achieved as instructions may take multiple cycles

Clever use of multiple ALUs allows for more than one instruction to be completed per cycle


Clocks Run The Engine

Clock speed is not a good indicator of speed Only good to compare CPUs in same brand Other factors such as RAM and clock speed

Clock speed of the front-side bus▪ Nervous system of computer

▪ Electrical pathway that connects CPU, RAM, hard drive

Memory▪ Working memory of the computer

▪ Fast memory built into the CPU chip

▪ Having to save to disk is slooooooow


Summary

From the transistors to the CPU to the instructions, computers are well-structured Explicit transistor layouts printed out en masse

Binary instructions connecting memory, input, output, and the logic units

Logic follows logic Despite our experience, computers are not

vindictive or cruel Unless someone programs them that way


fluency with information technology 2012-04-25katherine deibel, fluency in information technology 1...

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