Computing and Networks
Week 1
LBSC 690
Information Technology
Goals
•	By the end of this class, you will…
–	Understand what makes stupid computers seem smart
–	Have ways to think about “space,” “time” and “speed”
–	Know how the Internet got its name

Teaching Theater Introduction
•	Logging on
–	Userid and password are your university account

•	Directories
–	Your personal directory (to save notes) is at M: 
–	Nothing on the C: drive is saved!!!

•	Getting to notes you take from home
–	http://ttclass.umd.edu
Agenda
•	What “computers” do

•	How they do it

•	About the course

A Very Brief History of Computing
•	Hardware
–	Mechanical: essentially a big adding machine
–	Analog: designed for calculus, limited accuracy
–	Digital: early machines filled a room
–	Microchips: designed for missile guidance
•	Software
–	Numeric: computing gun angles
–	Symbolic: code-breaking
Commercial Developments
•	Mainframes (1960’s)
–	IBM
•	Minicomputers(1970’s)
–	DEC
•	Personal computers (1980’s)
–	Apple, Microsoft
•	Networks (1990’s)
–	Web
•	Convergence (2000’s)
–	Cell phone/PDA, HDTV/Computer, …

The Big Picture
Binary Data Representation
Hardware Processing Cycle
•	Input comes from somewhere
–	Keyboard, mouse, microphone, camera, …

•	The system does something with it
–	Processor, memory, software, network, …

•	Output goes somewhere
–	Monitor, speaker, robot controls, …
What is a computer?
Computer Hardware
•	Central Processing Unit (CPU)
–	Intel Xeon, Motorola Power PC, …
•	Communications “Bus”
–	FSB, PCI, ISA, USB, Firewire, …
•	Storage devices
–	Cache, RAM, hard drive, floppy disk, …
•	External communications
–	Modem, Ethernet, GPRS, 802.11, …

Units of Frequency
Units of Time
The Storage Hierarchy
•	Speed, cost, and size: 
–	You can easily get any 2, but not all 3

•	Fast memory is expensive
–	So large memory is slow!
–	But fast access to large memories is needed

•	Solution:
–	Keep what you need often in small (fast) places
•	Keep the rest in large (slow) places
–	Get things to the fast place before you need them
Best of Both Worlds
Locality
•	Spatial locality: 
–	If the system fetched x, it is likely to fetch data located near x

•	Temporal locality: 
–	If the system fetched x, it is likely to fetch x again
System Architecture
Everything is Relative
•	The CPU is the fastest part of a computer
–	3 GHz Core 2 Duo = 6,000 MIPS
•	3 operations per processor every nanosecond

•	Cache memory is fast enough to keep up
–	128 kB L1 cache on chip (dedicated, CPU speed)
–	4 MB L2 cache on chip (shared, CPU speed)

•	RAM is larger, but slower
–	1 GB or more, ~6 ns
Units of Size
The Storage Hierarchy
“Solid-State” Memory
•	ROM
–	Does not require power to retain content
–	Used for “Basic Input/Output System” (BIOS)
•	Cache (Fast low-power “Static” RAM)
–	Level 1 (L1) cache: small, single-purpose
–	Level 2 (L2) cache: larger, shared
•	(“Dynamic”) RAM (Slower, power hungry)
–	Reached over the “Front-Side Bus” (FSB)
•	Flash memory (fast read, slow write EEPROM)
–	Reached over USB bus or SD socket
–	Used in memory sticks (“non-volatile” storage)

System Architecture
“Rotating” Memory
•	Fixed magnetic disk (“hard drive”)
–	May be partitioned into multiple volumes
•	In Windows, referred to as C:, D:, E:, …
•	In Unix, referred to as /software, /homes, /mail, …
•	Removable magnetic disk
–	Floppy disk, zip drives, …
•	Removal optical disk
–	CDROM, DVD, CD-R, CD-RW, DVD+RW, …
How Disks Work
Trading Speed for Space
•	Hard disk is larger than RAM but much slower
–	typical: 10 ms access time, 100 GB (at 5400 rpm)
•	One thousand times larger than RAM
•	10 million times slower than the CPU!
•	The initial access is the slow part
–	Subsequent bytes sent at 17 MB/sec (60 ns/byte)
•	As “virtual memory,” makes RAM seem larger
–	But too little physical RAM results in “thrashing”

Discussion Point: Moore’s Law
•	Processing speed doubles every 18 months
–	Faster CPU, longer words, larger cache, more cores
•	Cost/bit for RAM drops 50% every 12 months
–	Less need for “virtual memory”
•	Cost/bit for disk drops 50% every 12 months
–	But transfer rates don’t improve much

•	Why????
Breaks
•	Typically, two breaks
–	10 minute break after the first hour
–	5 minute break after the second hour

•	No food or drink in the teaching theater
Who’s faster?
•	Intel Pentium 4 (2004): 3.80 GHz

•	Intel Core 2 Duo (2008): 2.6 GHz

RAID-5
•	Disks can fail in two ways:
–	Bad sectors (data sectors, directory sectors)
–	Mechanical failure

•	RAID-5 arrays “stripe” blocks across disks
–	“Parallel” data transfer is faster than “serial”
–	~30% “parity” allows reconstruction if one disk fails
Tape Backup
•	Tapes store data sequentially
–	Very fast transfer, but not “random access”

•	Used as backup storage for fixed disks
–	Weekly incremental backup is a good idea
•	With a complete (“level zero”) monthly backup

•	Used for archival storage
–	Higher data density than DVD’s
Discussion Point: Migration
•	What format should old tapes be converted to?
–	Newer tape
–	CD
–	DVD

•	How often must we “refresh” these media?

•	How can we afford this?
Discussion Point: 
What’s Special About Computers?
Course Goals
•	Conceptual
–	Understand computers and networks
–	Appreciate the effects of design tradeoffs
–	Evaluate the role of information technology
•	Practical
–	Learn to use some common tools
–	Solve a practical problem
–	Develop a personal plan for further study
Some Motivating Questions
•	What are the technical implications for:
–	Privacy? 
–	Copyright?
•	How will digital repositories develop?
–	How will they interact with distance education?
–	What are the implications for archives?
•	How might electronic dissemination impact:
–	Roles of authors, publishers, and readers?
–	Access by disenfranchised populations?
Some LBSC Courses on IT
•	708E	E-Government
•	708Q	Digital Preservation
•	708T	Transformational Technologies
•	708X	E-Discovery
•	715	Knowledge Management
•	733	Networks 
•	790	Programming for User Interfaces
•	793	Database Design 
•	795	Human-Computer Interaction
•	796	Information Retrieval Systems
Instructional Staff
•	Professor: Dr. Doug Oard
–	Offices: HBK 4121G/AVW 3145
–	Email: oard@umd.edu (finds me anywhere)

•	Teaching Assistant: Nishita Thakker
–	Office: TBA
–	Lab time+location TBA
–	Email: nthakker (at) umd.edu

•	Teaching Theater Technician
Approach
•	Readings
–	Provide background and detail

•	“Socratic” sessions
–	Provide conceptual structure

•	“Practicum” sessions, homework, project
–	Provide hands-on experience

•	Quiz, exams
–	Measure progress
The Grand Plan
A Personal Approach to Learning
•	Work ahead, so that you are never behind

•	Find new questions everywhere
–	Then find the answers somewhere

•	Enrich your practical skills relentlessly

•	Pick topics you want to learn more about

•	Start thinking about your project soon
–	Pick partners with complementary skills
Obtaining Recordings
•	All classes recorded
–	Fixed camera angle with screen in field of view
–	Microphones in the ceiling

•	Usually available over the Internet
–	Postage-stamp video, some audio distortion
–	Useful for seeing what slide we were on

•	Videotapes available outside my office
–	Please don’t take for more than 24 hours
Getting From Here to There
Grading
•	35-38% individual work
–	Exams: 25% for the best, 10% for the other
•	12-15% your choice (individual or group)
–	3% each for best 5 of the 7 homework/quiz
•	40% working in 3-person project teams
•	10% for demonstrated thought leadership
–	In class, on the mailing list, in your groups
Some Observations on Grading
•	One exam is worth more than all the homework
–	Message:  Use the homework to learn the material

•	Midterm grades predict final grades well
–	Message: Develop sound study skills early

•	You need not be good at everything to get an A
–	But you do need to be excellent at several things
The Fine Print
•	Group work is encouraged on homework
–	But you must personally write what you turn in

•	Deadlines are firm and sharp
–	Allowances for individual circumstances are included in the grading computation

•	Academic integrity is a serious matter
–	No group work during the exams or the quiz!
–	Scrupulously respect time limits
Course Materials
•	Readings

•	Optional Textbook

•	Daily access to a networked computer!
Computing at Maryland
•	Computer Labs
–	HBK 2018 (posted hours)
–	PG2 WAM lab (24 hours)
–	Need an OIT  “LPCR” account for printing

•	Sailor dial-in access
–	http://www.sailor.lib.md.us/help/ppp
Homework Goals
•	Think about relative speed and relative size

•	Interpret specifications for computer systems

•	Try some “back of the envelope” calculations

•	Some helpful hints:
–	There is a calculator in Windows accessories
–	If you’re rusty on math, the TA can help in lab
Team Exercise
•	Form into groups of 4
–	Be sure you have someone who has used Excel before in your group

•	Answer question 1(d) from the Fall 1996 final exam (available on the course Web site)
Network
•	Computers and devices connected via 
–	Communication devices
–	Transmission media
Why Network?
•	Sharing data
•	Sharing information
•	Sharing hardware
•	Sharing software
•	Increasing robustness
•	Facilitating communications
•	Facilitating commerce

Packet vs. Circuit Networks
•	Telephone system (“circuit-switched”)
–	Fixed connection between caller and called
–	High network load results in busy signals

•	Internet (“packet-switched”)
–	Each transmission is routed separately
–	High network load results in long delays
Packet Switching
•	Break long messages into short “packets”
–	Keeps one user from hogging a line

•	Route each packet separately
–	Number them for easy reconstruction

•	Request retransmission for lost packets
–	Unless the first packet is lost!
Networks of Networks
•	Local Area Networks (LAN)
–	Connections within a room, or perhaps a building

•	Wide Area Networks (WAN)
–	Provide connections between LANs

•	Internet
–	Collection of WANs across multiple organizations
Local Area Networks
•	Within a campus or an office complex
–	Short-distance lines are fast and cheap
–	Fast communications makes routing simple
•	Ethernet is a common LAN technology
–	All computers are connected to the same cable
•	Ordinary phone lines can carry 10 Mb/sec
•	100 Mb/s connections require special cables
•	1 Gb/s connections require special switches
–	Every host broadcasts everything to all others
•	Collisions limit throughput to about 50% utilization
Shared Network
•	All attach to the same cable
–	Ethernet and “cable modems”
•	Transmit anytime
–	Collision detection
–	Automatic retransmission
•	Inexpensive and flexible
–	Easy to add new machines
–	Robust to computer failure
•	Practical for short distances
–	Half the bandwidth is wasted
Switched (“Star”) Network
•	All attach directly to a hub
–	Switched Ethernet
–	Digital Subscriber Lines (DSL)
•	Higher cost
–	Line from hub to each machine
–	Hub must handle every packet
–	Hub requires backup power
•	Much higher bandwidth
–	No sharing, no collisions
–	Allows disks to be centralized
Local Area Networks
Wireless Networks
•	Radio-based Ethernet
–	Effective for a few rooms within buildings
•	“Access Point” gateways to wired networks
–	Available throughout most of the Maryland campus
–	Commercial providers offer “hot spots” in airports, etc.
•	“WiFi WLAN” is available in several speeds
–	IEEE 802.11b: 10Mb/s (good enough for most uses)
–	IEEE 802.11g: 54Mb/s (required for wireless video)
–	IEEE 802.11n: 248Mb/s (and longer range)
•	Computer-to-computer networks are also possible
–	“Bluetooth” is the most common (very short range)
Wide Area Networks
•	Campus, regional, national, or global scale

•	Expensive communications must be used well
–	Limiting to two hosts allows 100% utilization

•	Routing is complex with point-to-point circuits
–	Which path is shortest? Which is least busy? …

Maryland’s Campus Network
The Internet
•	Global collection of public “IP” networks
–	Private networks are often called “intranets”

•	Independent
–	Each organization maintains its own network

•	Cooperating
–	Internet Protocol (IP) address blocks
–	Domain names
–	World-Wide Web Consortium (W3C)
–	Computer Emergency Response Team (CERT)
Overview
A Short History of the Internet
•	1969: Origins in government research 
–	Advanced Research Projects Agency (ARPAnet)
–	Key standards: UDP, TCP, DNS
•	1983: Design adopted by other agencies
–	Created a need for inter-network connections
–	Key standards: IP
•	1991: World-Wide Web added point-and-click
–	Now 150 million Internet “hosts”
–	Key standards: HTTP, URL, HTML, XML
Internet  Web
•	Internet: collection of global networks

•	Web: way of managing information exchange
–	More details on this next week

•	There are many other uses for the Internet
–	File transfer (FTP)
–	Email (SMTP, POP, IMAP)

Thinking About Speed
•	Speed can be expressed two ways:
–	How long to do something once?
•	Memory speed measured as “access time”
–	How many things can you do in one second?
•	Processor speed measured in “instructions per second”

•	Convenient units are typically used
–	“10 microseconds” rather than “0.00001 seconds”
Some Definitions
•	Latency
–	The amount of time it takes data to travel from source to destination

•	Bandwidth
–	The amount of data that can be transmitted in a fixed amount of time
The Complete Picture
Before You Go
	On a sheet of paper, answer the following (ungraded) question (no names, please):

	What was the muddiest point in today’s class?