The Digital Deluge Lecture 3 Learning in Retirement

The Digital Deluge Lecture 3 Learning in Retirement David Coll Professor Emeritus Department of Systems and Computer Engineering Winter 2009

What are “Computers” Anyway? • Computers are digital machines that can acquire or create, store/retrieve, process, display, and communicate information in the form of finite binary numbers. • A computer is an electronic machine composed of three parts – Input/Output – Memory – Central Processor Unit

INPUT CENTRAL PROCESSING UNIT C PU MEMORY “BUS” 3 OUTPUT

• 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

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 6

Address Word Length 0000001 M e m o r y S i z e 000002 000003 000004 000005 1048576 7

Memory Address Content 0000 10100111 01101000 11001001 1111 0001 0010 0011 0100 0101 0110 0111 1000 1001 --1111 8

• 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”

CPU 10

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 11

• 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 •

Instruction Format OP CODE OPERAND ADDRESS 13

• 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.

Instruction Cycle • FETCH – Get the contents of the Memory Location whose address is in the Program Counter. – Put the contents of the Operation Code Field in the Instruction Register. – Put the contents of the Address Field in the Address Register – Increment the Program Counter. • EXECUTE – Carry out the instruction in the Instruction Register on the data referred to by the contents of the Address Register 15

Addition 1 01100001 A 11100101 B LDA A 01111011 ADD B C STA C 16

PC 23 STA C 87 276 A 88 513 AR ADA B 25 ACC LDA A 24 IR B C THEN WHAT DOES THE COMPUTER DO? 17

• What is the most important instruction? • [Answer: HALT].

Input-Output Units • Input Units: keyboard, scanner, modem, external disk memory, analog-to-digital converter, camera, sensor. • Output Units: screen, printer, modem, external memory; digital-to-analog converter, controller. 19

• OK, so that sort of explains how a digital computer works: • In a nutshell – the set of operations required to solve the problem at hand • add up the bills, or print the characters in a book, or whatever, – are expressed in a program (a list of instructions that when executed achieve the desired result); and the program is ’run’, i. e. , the individual instructions are carried out – one after another …

Introduction • The Digital Deluge – the flood of information pouring over the world and beyond, is a communications phenomenon. • The information representation is digital in in nature, and is handled by computers • The computers have evolved to positions of immense processing power on gigantic sets of data very rapidly, but • It is the information communication systems that make the phenomenon global.

Information Communications Technology • Telephone and messaging services to all parts of the world • Worldwide digital communications • Worldwide connectivity via the Internet and the World Wide Web • Access to information of all kinds • Text, Images, TV

ICT Services and Applications • Multimedia* Information Storage, Retrieval, Distribution, and Processing • Messaging: IM, email • Conferencing • Telemetry, Telematics • Reservations and Scheduling • Inventory and Catalog Management • Command Control • Billing, Accounting, Paying * Audio, Video, and Data

Applications Enabled by ICT • • Voice, Video and Data Communications E-Commerce Entertainment Multimedia Broadcasting Social Networking Banking and Financial Transactions Publishing Supply Chain Management

More … • • • Transportation and Travel Property Management Education Medicine, Health, and Pharmacology Security Military Affairs Justice Industry Science

How the information gets to us • We’ve looked at how information becomes digital and why. • Now, let’s briefly look at how this digital information gets to us • And why it’s a ‘good’ thing to deliver it using digital technology

How Did We Get to Where We Are • We started (1845) with simple handkeyed Morse code telegraphy • Moved to telegraphy and teletype communications

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 was, she was walking down the street, is : • do-wah-diddydum-diddy-do

Teletypewriter Service ASR 33 – Teletype Machine Binary Coded Characters

ASCII Code Set A = 11000001 a = 11100001

Teletype Service • “A printing telegraph system that replaced the sending key with a typewriter-like keyboard and the receiving sounder with a teleprinter. • Western Union introduced teletypewriter service in 1923 so that companies could link branches and even join other companies in private text messaging over leased privateline networks.

• “Teletype service was heavily used by banks, telephone companies, electric utilities, and others into the early 1970 s”. (http: //www. yourdictionary. com/teletype) • Canada: CN and CP – CNCP Telecommunications – Rates: 110 - 300 bps – (10 11 -bit characters per second) • Teletypewriters were used as the terminals for minicomputers in the early ‘ 60 s, hence the ASCII Code Set became a de facto standard 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 for both inputs and outputs. • First, data sources … which require high transmission rates communicate directly with the SAGE computer by means of digitally-coded data transmitted at 1300 pulses per second over voice-bandwidth telephone lines and radio channels. • Typical applications of this type of channel are inputs from search radars and intercommunication between adjacenters.

MIT Lincoln Lab SAGE Center - 1957

• “Teletype provides a second channel which is slower but equally automatic. • … voice telephone communications are used in cases where high automaticity is either unnecessary, too expensive, or not feasible. • If such information must be entered into the computer, either punched cards or operator keyboard inputs are used. ”

Then What? • Introduced voice telephone networks (1876) • Moved to digital technology within these • Then to the provision of data communication networks of two types: – the TDM synchronous, circuit-oriented, networks of the telephone industries and – the best-effort, packet-switched, internetworking strategies of the US Do. D Arpanet, which grew into the Internet and gave us the IP Networks of today.

Where Are We Today? • A ubiquitous, world-wide, broadband, multimedia, IP-based network – with a large set of communication services – serving an immense array of applications dependent on Information and Communications Technology (ICT) – which are available to enable and support all aspects of modern society.

Where Are We Now? Let me start by telling you something about how data communications works.

Early 21 st 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.

Shared Circuits - Multiplexing • Telephone wires and cables are expensive and must be shared • Your telephone call is multiplexed (combined) with thousands of others on a time-sharing basis on very high capacity digital transmission links as it moves along the established ‘circuit’ from one signal switch to another on its way to the destination. • This is called time division multiplexing

Time Division Multiplexing 1 2 3 In telephony each source is sampled 8, 000 time per second 1 2 3 Time, seconds

TDM Applications • • • Digital Telephony Data Communications Satellite Access Optical Fibre Cellular Radio

Data Communications • The digital time division multiplexed telephone (TDM) networks, based on 64 kbps digital voice channels, are the major carriers of data communications as well. • Data transmission rates on the world’s telecommunication networks vary from 56 kbps from a voiceband modem on your phone line to 1. 5 Mbps, or so, on DSL, to 10’s of Terabits per second on optical fiber trunks.

Digital TDM Hierarchy

SONET Rates Optical systems now carry 160 OC-192 signals using l. DM on a single fibre, and many cables carry 40 fibers That’s 8, 000, 000 bytes per second= 80 TBps

Computer Communications A parallel system of modern networks started with what some call “computer communications”, more properly referred to as “packet-switched communications” that grew out of a solution to requirements of the US Do. D for command control messaging networks that could survive nuclear war.

Bursty Data • The idea of sending information in packets is based on the observation that computer data is “bursty”. • This made perfectly good sense – at the time. • After all, the only time when data had to be communicated was when you hit the “ENTER” key on your keyboard and the contents of the keyboard memory buffer had to be sent to the mainframe, or when a screen full of characters had to be sent, or an email sent.

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

Circuit Sharing • The idea of using packets – short blocks of data together with addressing information – for communications between computers, in a day when telephone or data line charges were high, allowed the line to be shared in a simple way – first you, then me: • the Aphonse-Gaston protocol for getting through a narrow doorway.