Transcript Digital Basics

Digitizing information
• Information is knowledge in a form that is
understandable to humans
• Digital data are information that have been
transformed to be understandable to
computers
– Computers are getting smarter all the time, so maybe
we should say that information is digitized for digital
devices or transformed into continuous patterns for
analog devices (humans are considered mainly analog
devices)
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Data Representation
• Digital data are any data (text, audio, video,
touch, optics, numbers) that are represented by
a bit pattern (such as 00011100011000)
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Bit: binary digit
Can be represented by different voltage levels
Or orientation of magnetic particles
Or different frequencies , amplitudes, and/or phases
• Analog data is represented by an infinite scale
of continuous values.
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How to represent numbers?
Binary system (non-negative integers)
Base 2
Base 10
000000
0
000001
1
000010
2
000011
3
000100
4
000101
5
000110
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000111
7
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How to represent the digit 9?
• All characters that we type on a keyboard
are transmitted as a bit pattern
• ASCII encoding uses 7 bits
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http://www.neurophys.wisc.edu/comp/docs/ascii/
Some encoded values are non-printable
Extended ASCII (8 bits) encodes 128 additional
symbols
Unicode represents many language characters
http://www.unicode.org/versions/Unicode6.0.0/
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Growth of social media
• Social networking sites
– Facebook, linkedln, YouTube, etc.
• Blogs
• Twitter
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How is sound represented?
• On your analog phone line and phonograph
records, a sound wave is sent/recorded in
proportion to the input
• When sound is digitized it is sampled and
quantized
• Analog representation conceptually should
be more accurate than digital information
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How are images represented?
• 2-Dimensional sampling (perhaps)
– Each sample is called a pixel (picture element)
– It can be represented by 1 bit for black or white
(FAX messages)
– Each pixel may require 24 bits (8 for each of
the colors of red, green, blue)
• Various compression schemes are usually
applied (lossy or lossless)
• More levels provide better resolution
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Advantages of digitizing
• Sampling errors are not cumulative
• Small errors can be detected and corrected
• It is easier to integrate different types of
digitized information into one bit stream
than manipulate analog representations
• The same circuitry is used for different
applications
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Bits and byte
• A byte was initially defined as a character
encoding (so that, on some machines, a 6 or
7 bit pattern was called a byte)
• Today a byte is generally considered to be 8
bits
– Typically 8 bits are the number of bits used to
represent a character
• Even 7 bit ASCII encoding will be padded to 8 bits
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Metrics used
• Transmission speed is characterized in bps
(bits per second or b/s)
– 802.11 transmission speeds are typically given
in some multiple of Mbps (1000000 bits/s)
• Storage capacity is usually given in bytes
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4TB envisioned for hard disks
TB is 1024*1024*1024*1024 bytes
GB is 1024*1024*1024 bytes
MB is 1024*1024 bytes or 220 bytes
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Circuits and Chips
• Pulses flow over circuits
– We’ll say two states – perhaps 5 volts to
represent a 0 and -5 volts to represent a 1.
• Timing is critical in order to separate two
pulses that may each represent a 1.
• Computer chip (or integrated circuit) is
manufactured with wires (for delivery),
capacitors (store the charges), transistors
(amplify and switch voltages)
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Materials used
• Silicon and geranium are typically used for
semiconductors because of good conducting
and insulating properties
• Process is miniaturized
• Integrated circuits (chips) are packaged in
protective carriers
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Combining chips
• Components are housed on a motherboard
(system board)
– System boards contains buses to interconnect
the chips
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Programs and Instructions
– The Operating System is written by a
programmer in a programming language such
as C# or C (with a few lines of assembler).
– Application programs may be written in a
programming language such as Java or C++.
– Web pages are written in programming
languages such as html or xml.
– Sometimes graphical tools are used to write
programs
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Source code/ executable code
• Translator translates the source code to
machine code
– Compiler translates source code to object code, with
instructions that can be repeatedly executed once
translated
– Interpreter translates and executes source code one
statement at a time
• “Machine code” is directly executable by
the hardware
– Instruction is a set of op codes and operands
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Inside the processor
• Control Unit
– Interprets op code and sends signals to the
different registers for transferring data
• ALU (arithmetic logic unit)
– Add, multiply, shift, compare, etc.
• Registers
– Temporarily hold data
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Instruction Cycle
• Von Neumann architecture
– Data and program are stored in main memory
– Instructions are executed sequentially unless
they explicitly override this order
• Instruction cycle
– Instruction is fetched, decoded, pointer to next
instruction is incremented
– Instruction is executed
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Executing an instruction
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Fetch the instruction from memory
Decode the op code (say “add two operands”)
Increment the program counter (concurrently)
Send signals to different units to execute, e.g.,
– Fetch first operand from memory; send to ALU
– Fetch second operand and send to ALU
– Give signal to ALU to add
– Result will be in register – send it to specified register.
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Computer networks
• Computer Network: Set of computers and
associated devices together with a
communication infrastructure
– Links
– Routers
– Software and firmware protocols
• Originally developed for businesses and
Universities
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The Internet &Personal
Computers
• Personal computers became widespread
• The Arpanet was developed for national security purposes
(Cold War)
– DoD provided for the commercialization of the Internet
– Networked computers are used for
1) social networking
2) Email
3) Games
4) Hosting the World Wide web
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World Wide Web
• Collection of linked files
– Digitized graphics, sound, documents, etc.
– The Internet is the infrastructure for the Web
• Why might a web site be unavailable?
– Your computer or local connection may be
malfunctioning
– The Internet may be down
– The Site may be down or overloaded
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Cloud Computing
• Applications, Data Storage, Search, ecommerce and Web Information are all in
the cloud
– Basically high speed computers, high speed
communication lines, huge storage systems
• If your email files and application data are
in the cloud, you can access them anywhere
with a mobile device
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Cloud computing
• You do not have to maintain hardware and
software or personnel for the maintenance
• You need not add more memory
• You do not have to worry about crashes
• You do not have to upgrade your system
• Provides mobility
– You can’t work without an Internet connection
• Is it more or less secure?
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Convergence
• Several technologies with different
functionalities evolve to form a single
product
– Smart phones,
• Camera, music player, movie player, email,
telephony, compass, calendar, game console,
ebooks, web access
• iPhone hard Disk (64GB) filled with pictures
• apps
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The Digital Divide
• Gap between earning power and education
of those who understand and have digital
technologies and those who do not.
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Privacy and digital technology
• Surveillance by government
– Enabled by computers & networking
• Social media
– Teenagers & others tend to place personal
information on these sites
• Identity theft
– Hackers breaking into databases
• Cookies, gathering of marketing information
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Intellectual Property
• Software is soft
– Illegal copies of music & video were previously
common but of poorer quality
– Software copies are of equal quality as the
original
– Easier and faster to copy
– What rights do developers have?
– Patents????
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A further look at security
• Basic services that a system should provide:
– Confidentiality
• Prevent unauthorized access to information
• Chief mechanism: encryption
– Integrity
• Prevent unauthorized modification of information
• Sample mechanism: error detecting code attached
– Availability
• Sample mechanism: redundancy
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Secure your computer
• Do not download applications unless you
are sure of their integrity.
• Uninstall programs that you no longer use.
• These steps will aid performance as well as
security.
– Storage
– Processor speed
• Cloud computing aids some of these issues
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User IDs and Password
• Strong passwords prevent use of:
– Dictionary words
– Less than 8 characters
• System may require frequent change of
passwords
• System may keep history of previous
passwords used
– Passwords should not be kept on your desk
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Suggestions for password usage
• Use numbers, upper and lower case letters
• Change passwords often
• Try to use same ID for many accounts– Perhaps with some part of site attached
• Have low-security account for mundane
matters with same simple password
• Have high-security account with strong
password
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What if you forget password?
• Typically, it is mailed to your (previously
stated) email account
• May require a personal question
• How do you access the cloud?
– How secure is your password for cloud
computing?
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Password theft
• Intruder can possibly obtain credit cards
numbers and other personal information
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Shoulder surfing
Dumpster diving
Network sniffing
Brute force attack
Phishing – link to a fake site
Keylogging, spam
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Standalone password manager
• User is assigned a single (secure) password
to access the password manager
• Manager keeps track of accounts and
passwords (even generate them) in
encrypted form
• Some password managers are free,
shareware, or open source
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