Administrivia

• Has everyone been to the course web site?• First assignment ready – pick it up on web• Labs to begin Monday

– Lab times: TWTH 7:30pm – 10:30pm– Location : Friend 006/007– Details Pick up lab on web, read it, do it; go to

lab to get help or use the computers if you like.

• Questions??

What Does a Computer Do?

Whatever I tell it to do

• I say: Add 2 and 3 and show me the result– Computer says: 5

• I say: Multiply that result by 7 and show me the result– Computer says: 35

• I say: Show me the home page of the Princeton CS department– Computer says:

What’s Going On?

• Who’s doing the work?

• How do I tell it what to do?

The Ghost in the Machine• Read an input and memorize it• Read another input and memorize it• Add the inputs and display result• Read input and memorize it• Multiply input with previous result and display the result

• Hardware does the work• Programmer writes a program for the machine• Program tells hardware what to do at each step

• But not in English: In a computer programming language …

What Programs Look Like

read (a)

read (b)

c = a + b

read (d)

e = d * c

print (e)

; Read first input and store it in variable a

; Read second input and store it in variable b

; Add the values of a and b and store the result in variable c

; Read third input and store it in variable d

; Multiply the values of c and d and store the result in variable e

; Display the value of variable e

• The computer takes each of these instructions and executes it

The Computer’s Job

• Computing outputs from inputs by performing operations

• Representing and translating information

• Storing, reading and writing data to/from memory

• Accepting inputs from and producing outputs to the external world (keyboards, displays, printers)

• Sequencing steps

• Maintaining state

• Networking

• Compiling and managing programs

Computer’s Job: Compute Outputs from Inputs

CPU

out = in1 + in2

2

3

5in1

in2out

Computer’s Job: Read/Write Variables From/To Memory

CPU

c = a + b

a

c

b

2

5

3

c = a + b

2

3Memory

5

Computer’s Job: Input and Output

CPU

Memory

2

read (a)

2

a

c

b

2

read (a)read (b)

print (c)c = a + b

Computer’s Job: Input and Output

CPU

Memory

3

3

read (b)

a

c

b

2

3

read (a)read (b)

print (c)c = a + b

Computer’s Job: Input and Output

CPU

Memory

a

c

b

2

5

3

c = a + b

2

3

5

read (a)read (b)

print (c)c = a + b

Computer’s Job: Input and Output

CPU

Memory

read (a)read (b)a

c

b

2

5

3

print (c)

print (c)c = a + b

5

5

5

• How does computer understand “a”, “b”, “4”, etc.– i.e. data values?

• How does computer understand “read (a)”; that it should add its inputs, when to read from memory, when to take next step etc.– i.e. control

Computer’s Job: Representing and Translating Information

• Answer: Everything is represented as 1’s and 0’s– Computer only sees 1’s and 0’s– All data values, instructions etc are encoded as combinations of 1’s and 0’s

The World of 1’s and 0’s

CPU

c = a + b

010111001

0010

Memory0011

0101

0010

0011

0101

0000000001

00010

10011

11111

Computer’s Job: Sequencing

• Executing programs requires the computer to take several discrete steps, one after another

• A “clock” is an input to the CPU that orchestrates the sequencing – each time clock changes its value, CPU takes next step

• So there are lots of inputs to the CPU, of different types:– Data values (2, 3, etc)

– Program instructions (read a; c=a+b; etc)

– Clock

Computer’s Job: Maintaining State

• The computer also maintains “state” i.e. remembers information across steps of execution; e.g.– Holds results from previous step for use in next step

– Values of a,b and c in memory

– Internal state in CPU (later)

• Computer can be viewed as a “state machine.” It steps from one state to another based on the current inputs, including instructions, data and clock signal

• Except, it is a “programmable state machine.”The states and transitions it makes are not fixed in hardware or the same every it starts, but rather are controlled in part by program instructions which can be changed easily (in software)

Memory

CPU

Network

WebServer

AtPrinceton CS

Network Card

Graphics Card

Sound Cardhttp://www.cs.princeton.edu

Network

CPU

When user enters URL, CPU needs to fetch the page.

Network device sends request to web server www.cs.princeton.edu over the network (Internet)

Computer’s Job: Networking

CPU talks to a network device, asking it to request page corresp. to the URL

Memory

CPU

Network

WebServer

AtPrinceton CS

Network Card

Graphics Card

Sound Cardhttp://www.cs.princeton.edu

Network

WebServer

AtPrinceton CS

CPU

Web server sends reply (page) back, which network device receives

Network device forwards the page to CPU, which sends it to graphics device for rendering and then to display

Computer’s Job: Networking

Computer’s Job: Compiling and Managing Programs

• Convert high-level, human-readable programming languages, data representations and sequencing methods to machine-readable data, control and sequencing in 1’s and 0’s

– Compilers do this

• Manage hardware resources so that multiple programs can run at the same time (email, MS Word and MP3 Player), security is provided, etc.

– Operating systems do this

Summary: The Computer’s Job

• Computing outputs from inputs by performing operations

• Representing and translating information

• Storing, reading and writing data to/from memory

• Accepting inputs from and producing outputs to the external world (keyboards, displays, printers)

• Sequencing steps

• Maintaining state

• Networking

• Compiling and managing programs

Rest of the Course

• Hardware: Building a computer– How arithmetic and logical operations are realized– How data are represented– How memory is realized– How sequencing is done and state machines are realized

• Software: Programming and Using a computer– Programs and Programming languages– Algorithms– Applications: Graphics and Sound

• Operating Systems, Networking and Distributed Computing– Operating Systems– Basic Networking– Applications: E-mail and the Internet– Peer-to-peer and music sharing

• Hard Problems and Limits of Computing

• Security, Privacy, Artificial Intelligence

Let’s Go Buy a Computer

So What’s in a Computer?

• Processor brains• Memory scratch paper• Disk long term memory• I/O communication (senses)

• Software reconfigurability

What’s in a Computer?

CPUCommunications

I/OText

SoundSoftware

Power

Disk

RAM

Ports

Let’s Go Buy a Computer

Computer Configuration

• Processor (Pentium IV, 2.8 GHz)• RAM (512 MB of SDRAM (expandable))• Disk (80 GB)• CD ROM/ CD RW/DVD/…• 17" XGA TFT Display (1280 x 1024 res.) • 3.5" 1.44MB Floppy Disk Drive • S3 Savage IX 128-bit AGP 2x graphics

– 8MB memory, 3D Hardware acceleration, composite TV-Out support, …

• 16-bit Sound

Computer Configuration (contd)

• 2 Type-I or Type-II slots or 1 Type-III slot • 2 USB Ports • Built-in 56Kbps V.90 Data/fax modem • Built-in 10/100 Ethernet Adapter and

802.11b/g wireless

• Also – universal AC adapter, – built-in Lithium-Ion battery, – Microsoft Windows XP, – Encarta World Encyclopedia online version…

Putting Together an Application

• Word (is a part of the Office application)• Runs on Windows (an operating system)• Which runs on a Dell PC (a computer)• Which has a Pentium (a processor)• Enhanced by connections to monitor, printer, network• Uses random access memory (RAM) to work on

document, disk (non-volatile) memory to store in• Need a CD-ROM to install application (or install off

the Internet over a broadband connection)

What’s Special About a Computer?

• Most complex object made by humans• A rich communication mechanism for society• Amazing how it works• Reconfigurability• Moore’s Law

More for Less --Moore’s Law

• 1985 when I was a student here– A desktop machine in the lab

• $150,000 (now < $1,000)

• 700 KHz chip (now ~3 GHz)

• 1 MB memory (now 128-512 MB)

• 80 MB disk (now 80 GB +)

• CD-ROM had just been invented (83)

• Minimal Internet connection

• Communication to Internet 9600 bps (now 10 Mbps)

Moore’s Law (contd)

• $150,000 (now < $1,000)– Factor of 150

• 700 Khz processor (now 2 GHz chip)– Factor of 3000

• 1 MB memory (now 256MB)– Factor of 256

• 80 MB disk (now 40/80 GB)– Factor of 1000

• Communication 9600 bps (now 10 Mbps)

– Factor of 1000

An interesting example: Walmart/Microtel PC

• AMD 1.5 GHz Sempron processor with 3DNow! Technology• 128 MB DDR Memory, expandable to 2 GB• 20 GB Ultra ATA-100 Hard Drive / 5400 RPM• 52x CD-ROM drive• Integrated 10/100 Ethernet Connection• Integrated graphics up to 64 MB shared video memory• Integrated 5.1 Channel AC'97 Audio• Available drive bays: Two 5.25", one 3.5“• No operating system installed• Speakers, but no display

• Price: $198

Moore’s Law (contd)

year

log

(p

eo

ple

pe

r c

om

pu

ter)

Mainframe

Minicomputer

Workstation

PC

Laptop

PDA

???

* This slide and the next lifted from a presentation by David Culler

Moore’s Law (contd)

Itanium2 (241M )

nearly a thousand 8086’swould fit in a modern microprocessor

Processing & Storage

LNAmixerPLL basebandfilters

I Q

CommunicationSensingActuation

SOON:

The Rest of the Course

Rest of the Course

• Hardware: Building a computer– How arithmetic and logical operations are realized– How data are represented– How memory is realized– How sequencing is done and state machines are realized

• Software: Programming and Using a computer– Programs and Programming languages– Algorithms– Applications: Graphics and Sound

• Operating Systems, Networking and Distributed Computing– Operating Systems– Basic Networking– Applications: E-mail and the Internet– Peer-to-peer and music sharing

• Hard Problems and Limits of Computing

• Security, Privacy, Artificial Intelligence (?)

Hardware: Building a computer

• Start with simplest part – switch

• Build logic gates – AND/OR– Use to solve logic problems

• Build memory

• Build processing power– Arithmetic Unit

• Build simple programming language

• How to represent data

• How to manipulate data

• How to manage information

• Algorithms– Simple algorithms for sorting and searching

– Recursion

• Two special applications– Picture processing on the computer

– Sound processing on the computer

Programming and Using a Computer

Operating Systems

• Running programs– How do you programs run and communicate

• Resource Management– How do multiple applications share resources and run

“at the same time”

– How do you ensure that applications get their fair share

• Virtualization– How do you hide the details of different hardware from

the upper levels of software

• How do computers communicate– Protocols TCP/IP, HTTP, FTP, …

• The InterNet– What it is and where it came from

– How it transports email and displays web pages

• Differing network connections– Client/server vs. peer-to-peer

– How networks facilitate music sharing

Networking and Distributed Applications

Hard Problems and the Limits of Computing

• Hard problems– Problems unlikely to be solved in our lifetime

– Problems unlikely to be solved in millennia

• Undecidable problems– Problems that provably can never be solved

Security and Privacy

• Security– Preventing break-ins, eavesdropping, etc

– Using the hardness of problems

• Privacy– Systems are not secure

– How much information should be public

• Digital rights management– Old ideas of copyright law may not work

– When is sharing legal? Safe communication

– Should you send your credit card over the internet?

If we have time …

• How well can computers– Understand written text

– Understand spoken text

– Understand hand drawn pictures

– Play chess?

– Compose music

– Listen to music???

– “Enjoy” music?

• Possibly a look inside a big program