The Digital DelugeLecture 3

Learning in RetirementDavid Coll

Professor EmeritusDepartment of Systems and Computer

Engineering

Winter 2009

What are “Computers” Anyway?

• ComputersComputers are digital machines that can are digital machines that can acquire or create, store/retrieve, process, acquire or create, store/retrieve, process, display, and communicate information in the display, and communicate information in the form of finite binary numbers.form of finite binary numbers.

• A computer is an electronic machine A computer is an electronic machine composed of three partscomposed of three parts– Input/OutputInput/Output– MemoryMemory– Central Processor UnitCentral Processor Unit

3

MEMORY

CENTRAL PROCESSING UNITC PU

INPUT OUTPUT

“BUS”

• Data in the form of binary words• Can be moved

– From the input unit• to the memory or • to the processor

– From the memory• to the processor or • to the output unit

Components

• The Memory consists of a number of storage spaces, – each having a unique address,

• in which data in the form of finite-length binary numbers can be stored

• Instructions, in the form of binary numbers, are also stored in the memory

6

Instructions & the Basic Operation

• What the computer does is specified by INSTRUCTIONS

• An Instruction specifies:– what operation is to be performed on – what data, and – where to put the result

• Instructions are coded as binary words and stored in the same memory as the data

7

Word LengthAddress

000000

000001

000002

000003

000004

000005

1048576

8

MemoryAddress Content

0000 101001110001 011010000010 110010010011 111111110100

0101

0110

0111

1000

1001

---

1111

• The Central Processor Unit (CPU) consists of – a Program Counter, which holds the address

of the instruction being executed. – an Instruction Register, which holds the

instruction being executed– An Address Register, which holds the

address of the operand– An Arithmetic Logic Unit, which carries out

the “current instruction” i.e. the instruction “being executed”

10

CPU

11

Instructions

• There are instructions to – Move data– Perform arithmetic or logical operations on

data, including comparisons– Change the order in which instructions are

carried out– Control the machine and its peripherals

• The instructions stored in memory constitute a program.

• A single address computer instruction usually has two parts:– The Operation Code and the Operand– e.g., ADD B

• which, when executed– leaves the sum of the contents of the

Accumulator and the contents of Memory Location B in the Accumulator  

•  

13

Instruction Format

OP CODE

OPERAND ADDRESS

• When an instruction is executed• It is moved

– from the location indicated by the Program Counter

• into the Instruction Register• The Program Counter is incremented by

one• The operation and operand are ascertained• and the operation is carried out.

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Instruction Cycle• FETCHFETCH

– Get the contents of the Memory Location Get the contents of the Memory Location whose address is in the Program Counter.whose address is in the Program Counter.

– Put the contents of the Operation Code Field Put the contents of the Operation Code Field in the Instruction Register.in the Instruction Register.

– Put the contents of the Address Field in the Put the contents of the Address Field in the Address RegisterAddress Register

– Increment the Program Counter. Increment the Program Counter. • EXECUTEEXECUTE

– Carry out the instruction in the Instruction Carry out the instruction in the Instruction Register on the data referred to by the Register on the data referred to by the contents of the Address Registercontents of the Address Register

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Addition

11100101

01111011

11100101

01111011

1 01100001

A

B

01100001

C

LDA A

ADD B

STA C

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THEN

WHAT DOES THE COMPUTER DO?

LDA A

ADA B

STA C

276

23

513

24

25

87

88

PC IR ACC AR

A

B

C

• What is the most important instruction?

• [Answer: HALT].

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Input-Output Units

• Input UnitsInput Units: keyboard, scanner, modem, : keyboard, scanner, modem, external disk memory, analog-to-digital external disk memory, analog-to-digital converter, camera, sensor.converter, camera, sensor.

• Output UnitsOutput Units: screen, printer, modem, : screen, printer, modem, external memory; digital-to-analog external memory; digital-to-analog converter, controller.converter, controller.

• OK, so that sort of explains how a digital OK, so that sort of explains how a digital computer works: computer works:

• In a nutshellIn a nutshell– the set of operations required to solve the the set of operations required to solve the

problem at handproblem at hand• add up the bills, or print the characters in a add up the bills, or print the characters in a

book, or whatever, book, or whatever, – are expressed in a program (a list of instructions are expressed in a program (a list of instructions

that when executed achieve the desired result); that when executed achieve the desired result); and the program is ’run’, i.e., the individual and the program is ’run’, i.e., the individual instructions are carried out – one after another instructions are carried out – one after another ……

Introduction

• The Digital Deluge – the flood of information The Digital Deluge – the flood of information pouring over the world and beyond, is a pouring over the world and beyond, is a communications phenomenon.communications phenomenon.

• The information representation is digital in The information representation is digital in in nature, and is handled by computersin nature, and is handled by computers

• The computers have evolved to positions of The computers have evolved to positions of immense processing power on gigantic sets immense processing power on gigantic sets of data very rapidly, butof data very rapidly, but

• It is the information communication systems It is the information communication systems that make the phenomenon global.that make the phenomenon global.

Information Communications Technology

• Telephone and messaging services to all Telephone and messaging services to all parts of the world parts of the world

• Worldwide digital communications Worldwide digital communications • Worldwide connectivity via the Internet and Worldwide connectivity via the Internet and

the World Wide Webthe World Wide Web• Access to information of all kindsAccess to information of all kinds• Text, Images, TVText, Images, TV

ICT Services and Applications

• Multimedia* Information Storage, Multimedia* Information Storage, Retrieval, Distribution, and ProcessingRetrieval, Distribution, and Processing

• Messaging: IM, email Messaging: IM, email • ConferencingConferencing• Telemetry, TelematicsTelemetry, Telematics• Reservations and SchedulingReservations and Scheduling• Inventory and Catalog ManagementInventory and Catalog Management• Command and ControlCommand and Control• Billing, Accounting, PayingBilling, Accounting, Paying

* Audio, Video, and Data* Audio, Video, and Data

Applications Enabled by ICT

• Voice, Video and Data CommunicationsVoice, Video and Data Communications• E-CommerceE-Commerce• EntertainmentEntertainment• Multimedia BroadcastingMultimedia Broadcasting• Social NetworkingSocial Networking• Banking and Financial TransactionsBanking and Financial Transactions• PublishingPublishing• Supply Chain ManagementSupply Chain Management

More …

• Transportation and TravelTransportation and Travel• Property ManagementProperty Management• EducationEducation• Medicine, Health, and PharmacologyMedicine, Health, and Pharmacology• SecuritySecurity• Military AffairsMilitary Affairs• JusticeJustice• IndustryIndustry• ScienceScience

How the information gets to us

• We’ve looked at how information becomes We’ve looked at how information becomes digital and why.digital and why.

• Now, let’s briefly look at how this digital Now, let’s briefly look at how this digital information gets to usinformation gets to us

• And why it’s a ‘good’ thing to deliver it using And why it’s a ‘good’ thing to deliver it using digital technologydigital technology

How Did We Get to Where We Are

• We started (1845) with simple hand-We started (1845) with simple hand-keyed Morse code telegraphykeyed Morse code telegraphy

• Moved to telegraphy and teletype Moved to telegraphy and teletype communicationscommunications

J-38 Telegraph Key WWII Army Signal Corps http://www.pbase.com/boyett/image/70609670

Morse Code: Dots, Dashes, and Spaces

Morse Code

• Code Generator

• And the character to emphasize that there she And the character to emphasize that there she was, she was walking down the street, is :was, she was walking down the street, is :

• do-wah-diddy-diddy-do-wah-diddy-diddy-dum-diddy-do dum-diddy-do

Teletypewriter Service

Binary Coded Characters

ASR33 – Teletype Machine

ASCII Code Set

A = 11000001a = 11100001

Teletype Service

• ““A printing telegraph system that replaced A printing telegraph system that replaced the sending key with a typewriter-like the sending key with a typewriter-like keyboard and the receiving sounder with a keyboard and the receiving sounder with a teleprinter.teleprinter.

• Western Union introduced teletypewriter Western Union introduced teletypewriter service in service in 19231923 so that companies could so that companies could link branches and even join other link branches and even join other companies in private text messaging over companies in private text messaging over leased privateline networks.leased privateline networks.

• ““Teletype service was heavily used by Teletype service was heavily used by banks, telephone companies, electric banks, telephone companies, electric utilities, and others into the early 1970sutilities, and others into the early 1970s”. ”. (http://www.yourdictionary.com/teletype) (http://www.yourdictionary.com/teletype)

• Canada: CN and CP Canada: CN and CP – CNCP TelecommunicationsCNCP Telecommunications– Rates: Rates: 110 - 300 bps 110 - 300 bps – (10 11-bit characters per second)(10 11-bit characters per second)

• Teletypewriters were used as the terminals Teletypewriters were used as the terminals for minicomputers in the early ‘60s, hence for minicomputers in the early ‘60s, hence the ASCII Code Set became a de facto the ASCII Code Set became a de facto standard for computersstandard for computers..

MITRE: A Data Processing System for Air Defense R. R. Everett. Technical Director, MITRE Corp.; C. A. Zraket, Head, Advance Design Dept., MITRE Corp.H. D. Bennington, System Development Corp ; http://ed-thelen.org/sage.html

• ““Three types of data transmission are used Three types of data transmission are used for both inputs and outputs. for both inputs and outputs.

• First, data sources … which require high First, data sources … which require high transmission rates communicate directly transmission rates communicate directly with the SAGE computer by means of with the SAGE computer by means of digitally-coded data transmitted at 1300 digitally-coded data transmitted at 1300 pulses per second over voice-bandwidth pulses per second over voice-bandwidth telephone lines and radio channels. telephone lines and radio channels.

• Typical applications of this type of channel Typical applications of this type of channel are inputs from search radars and are inputs from search radars and intercommunication between adjacent intercommunication between adjacent centers. centers.

MIT Lincoln Lab SAGE Center - 1957

• ““Teletype provides a second channel Teletype provides a second channel

which is slower but equally automatic. which is slower but equally automatic.

• … … voice telephone communications are voice telephone communications are used in cases where high automaticity is used in cases where high automaticity is either unnecessary, too expensive, or not either unnecessary, too expensive, or not feasible. feasible.

• If such information must be entered into If such information must be entered into the computer, either punched cards or the computer, either punched cards or operator keyboard inputs are used.”operator keyboard inputs are used.”

Then What?

• Introduced voice telephone networks Introduced voice telephone networks (1876)(1876)

• Moved to digital technology within theseMoved to digital technology within these• Then to the provision of data Then to the provision of data

communication networks of two types: communication networks of two types: – the TDM synchronous, circuit-oriented, the TDM synchronous, circuit-oriented,

networks of the telephone industries and networks of the telephone industries and – the best-effort, packet-switched, the best-effort, packet-switched,

internetworking strategies of the US DoD internetworking strategies of the US DoD Arpanet, which grew into the Internet and Arpanet, which grew into the Internet and gave us the IP Networks of today. gave us the IP Networks of today.

Where Are We Today?

• A ubiquitous, world-wide, broadband, A ubiquitous, world-wide, broadband, multimedia, IP-based network multimedia, IP-based network – with a large set of communication services with a large set of communication services – serving an immense array of applications serving an immense array of applications

dependent on Information and dependent on Information and Communications Technology (ICT) Communications Technology (ICT)

– which are available to enable and support all which are available to enable and support all aspects of modern society. aspects of modern society.

Where Are We Now?

Let me start by telling you Let me start by telling you something about how data something about how data

communications workscommunications works.

Early 21st Century Telephony

• The voice signal generated by the microphone in your telephone set is transmitted along a twisted pair of copper wires to the nearest Local Office. – It is sampled 8000 times per second– The sample values are quantized

into one of 255 amplitude levels and

– represented by an 8-bit binary number: an octet or byte of 1’s and 0’s.

• Telephone wires and cables are Telephone wires and cables are expensive and must be sharedexpensive and must be shared

• Your telephone call is Your telephone call is multiplexed multiplexed (combined) with thousands of others on a (combined) with thousands of others on a time-sharing basis on very high capacity time-sharing basis on very high capacity digital transmission links as it moves digital transmission links as it moves along the established ‘circuit’ from one along the established ‘circuit’ from one signal switch to another on its way to the signal switch to another on its way to the destination.destination.

• This is called This is called time division multiplexingtime division multiplexing

Shared Circuits - Multiplexing

Time Division Multiplexing

332211

332211

1 32

Time, seconds

In telephony each source is sampled 8,000 time per secondIn telephony each source is sampled 8,000 time per second

TDM Applications

• Digital TelephonyDigital Telephony• Data CommunicationsData Communications• Satellite AccessSatellite Access• Optical FibreOptical Fibre• Cellular RadioCellular Radio

• The digital time division multiplexed The digital time division multiplexed telephone (TDM) networks, based on telephone (TDM) networks, based on 64 kbps digital voice channels, are the 64 kbps digital voice channels, are the major carriers of major carriers of data communicationsdata communications as well.as well.

• Data transmission rates on the world’s Data transmission rates on the world’s telecommunication networks vary from telecommunication networks vary from 56 kbps from a voiceband modem on 56 kbps from a voiceband modem on your phone line to 1.5 Mbps, or so, on your phone line to 1.5 Mbps, or so, on DSL, to 10’s of Terabits per second on DSL, to 10’s of Terabits per second on optical fiber trunks. optical fiber trunks.

Data Communications

Digital TDM Hierarchy

D Level Bit rate Mbps

Message Channels

DS0 0.064 1 DS1 1.544 24 DS2 6.312 96 DS3 44.736 672 DS4 274.176 4032

SONET Rates

OC Level Data Rate Mbps OC-1 51.840 OC-3 155.250 OC-9 466.560 OC-12 622.080 OC-48 2488.32

OC-192 9953.26

Optical systems now carry 160 OC-192 signals using DM on a single fibre, and many cables carry 40 fibers

That’s 8,000,000,000,000 bytes per second= 80 TBps

Computer Communications

A parallel system of modern networks A parallel system of modern networks started with what some call started with what some call

“ “computer communicationscomputer communications”,”,

more properly referred to as more properly referred to as

“ “packet-switched communicationspacket-switched communications”” that that

grew out of a solution to requirements of the grew out of a solution to requirements of the US DoD for command and control US DoD for command and control messaging networks that could survive messaging networks that could survive nuclear war.nuclear war.

Bursty DataBursty Data• The idea of sending information in The idea of sending information in

packets is based on the observation that packets is based on the observation that computer data is “bursty”. computer data is “bursty”.

• This made perfectly good sense – at the This made perfectly good sense – at the time.time.

• After all, the only time when data had to After all, the only time when data had to be communicated was when you hit the be communicated was when you hit the “ENTER” key on your keyboard and the “ENTER” key on your keyboard and the contents of the keyboard memory buffer contents of the keyboard memory buffer had to be sent to the mainframe, or when had to be sent to the mainframe, or when a screen full of characters had to be sent, a screen full of characters had to be sent, or an email sent. or an email sent.

• So, knowing that data is bursty one can So, knowing that data is bursty one can package each burst of data with the package each burst of data with the address of the sender and the address of address of the sender and the address of the recipient written on the face of the the recipient written on the face of the envelop and give it to the network to deliver. envelop and give it to the network to deliver.

Circuit Sharing

• The idea of using The idea of using packetspackets – short blocks of – short blocks of data together with addressing information – data together with addressing information – for communications between computers, in for communications between computers, in a day when telephone or data line charges a day when telephone or data line charges were high, allowed the line to be shared in a were high, allowed the line to be shared in a simple way – first you, then me: simple way – first you, then me:

• the Aphonse-Gaston protocol for getting the Aphonse-Gaston protocol for getting through a narrow doorway. through a narrow doorway.