InputOutput Systems and Secondary Memory

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Input/Output Systems and Secondary Memory
Lecture 7
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Electronic Digital Computers

• based on stored program design
• processor system
• CPU
• memory
• input/output system
• input/output devices
• secondary storage

Peripherals
Just about everything outside of the CPU/Main
Memory falls under the general classification of
a Peripheral Device
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I/O Subsystem

• Input/Output
• exchanging data and instructions between
• the user and the computer
• The user may be a human being, but it may
• also be a machine.like a car engine!
• Secondary Storage
• auxiliary storage for data and instructions

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Secondary Memory (Storage)

• Backup or alternative storage in place of
  (volatile) RAM
• cheaper, mass storage for long term use
• secondary memory devices (and media) are
  distinguished by their capacities, speed, and cost

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Types of Access

• RANDOM ACCESS
• items are independently addressed
• access time is constant
• DIRECT ACCESS
• items are independently addressed in regions
• access time is variablethough not significantly
• SEQUENTIAL ACCESS
• items are organized in sequence (linearly)
• access time is significantly variable

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Memory Hierarchy I
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Memory Hierarchy II
Flash Memory
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Secondary Memory

• SEQUENTIAL ACCESS STORAGE DEVICES AND MEDIA
  (SASD)
• magnetic tape
• DIRECT ACCESS STORAGE DEVICES AND MEDIA (DASD)
• magnetic floppy disks
• magnetic hard disks
• optical discs (CD-ROM/DVD)
• Flash Memory Cards

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Magnetic Tape

• stores data represented by magnetized particles
  in linear tracks
• magnetized clusters or domains are aligned to
  represent binary codes

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Longitudinal (9-track)
Magnetic Tape had a density of 6250 bits per inch
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Tape Drives in action1950s-80s
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Direct Access Storage Devices

• magnetic hard and floppy disks
• removable hard disks
• optical discs
• CD-ROM, CD-R, DVD
• DVD-R

GEOMETRY TRACKS and SECTORS
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Direct Access

• SEEK controller advances read/write head to
  proper track
• LATENCY waits for proper sector to rotate under
  head
• READ/WRITE disk head scans the sector for read
  or write

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Magnetic Disks

• FLOPPY DISKS
• 5.25 and 3.5 inch diskettes
• 1.44 2.88 MBytes capacity
• access drive speeds 600 r.p.m.
• inexpensive, archival uses for small amounts of
  data

• HARD DISKS
• 3.5 inch has approx 3,000 tracks per side
• multiple disk, sides (cylinders)
• high capacity 1 Terabyte
• access drive speeds 3,600 up to 7,200 r.p.m.
• on-line storage

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Floppy / Hard Disks
Hard Disk Drive
Floppy Diskfits in your shirt pocket !
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Disk vs. File Organization

• data is stored in blocks
• blocks occupy sectors
• sectors on tracks
• files have names
• files are indefinite in size
• files may be updated (in part or whole)

Files may become fragmented over time, which
causes data transfers to slow down
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Optical Discs

• Compact DiscRead Only Memory (CD-ROM)
• archived and published information
• Relatively high capacity (650 Mbytes)
• Compact DiscRecordable (CD-RW
• recordable
• readable using CD-ROM technology
• Digital Versatile Discs (DVD)/DVD-R)
• Very high capacity, read-only storages (5-15
  Gbytes)
• Multiple Layers, tighter spacing in the same size
  as CD
• Now BLUE RAY and DVD-HD! (3-10 times the capacity
  of todays DVDs)

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Optical Drives Reading and Writing

• discs are burnt one at a time
• high intensity laser beam used for
  reading/recording pregrooved tracks
• low intensity beam for reading/ higher intensity
  for burning

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Flash Memory Cards

• Non Volatile Solid State Memory
• Small, Convenient and Reliable up to gt10K writes
• Random Access
• Relatively expensive in terms of cost/Mb
• Prices dropping every day, capacity increasing!
• Bridging the Gap between CD-ROM and Dynamic Memory

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SanDisk Flash Card
One Gigabyte on a chip...and growing!
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The future disk technology

• Looks like a hard drive storage unit  but there
  are no moving parts inside.

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Output Peripherals

• video display monitors
• monochrome and color
• CRT and LCD
• printers
• character, line, and page
• sound and voice output
• MIDI synthesizers

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CRT technology

• cathode ray tube (CRT)
• phosphors excited by electron gun beams
• RGB composite color
• horizontal scanning pattern to refresh phosphors

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LCDs, How do they work?

• Way too complex to describe here!
• If you really want to know go to
• www.howstuffworks.com/lcd1.htm

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Printers

• CHARACTER
• dot matrix
• low-cost, text and graphic printers
• slow-speed, low quality
• inkjet
• medium-priced
• general-purpose

• PAGE
• laser printers
• high-quality
• assortment of sizes, performance, and cost

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Input Peripherals

• keyboard
• mouse
• scanners (flatbed, slide, and drum)
• digital cameras
• sound digitizers
• MIDI (Musical Instrument Digital Interface)
• Video digitizers

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Connecting all this stuff

• Parallel Bus
• Contains many signal paths for very fast data
  transfer
• Bulkier, expensive cable and connectors
• Limited distance capability
• Serial Bus
• Limited paths
• Lower cost, lower size, lower weight
• Longer distance (generally)

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Parallel / Serial Bus
Flat Parallel Computer Cable
Serial Computer Cable
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Where are parallel busses used?

• All of the paths inside the CPU and between the
  CPU, main memory and video processor are
  implemented using parallel busses for the very
  fastest transfer rates.
• Any plug in cards use parallel busses as well as
  internal magnetic and optical disk drives.
• Most of these busses are either 16 or 32 bits wide

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Where are serial busses used?

• Serial busses are primarily used to connect
  external devices and peripherals. The data
  transfer rates of peripherals connected via
  serial are generally much slower than those
  connected by parallel.
• Serial is convenient, relatively inexpensive and
  getting faster all of the time.
• The current serial standard for peripherals is
  called USB 2.0

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USB 2.0, Todays serial standard (2000)

• Max transfer speed of 400Mbps (Megabits per
  second), 40 times faster than the predecessor USB
  1.1
• Supports up to 127 devices connected to the same
  controller chip!
• A USB cable can be 5 meters long without causing
  any performance problems
• USB has become the ubiquitous serial connection
  standard for practically every external PC
  peripheral

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IEEE 1394, aka Firewire

• Another high speed serial bus in wide use is the
  Firewire bus, first introduced by Apple
• Similar in performance to USB 2.0
• Designed primarily for video devices such as
  camcorders, digital TVs, DVD devices and VCRs
• Many PCs today also include Firewire for use with
  Video authoring software and downloading video
  onto your computer

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USB 3.0!

• Standard introduced in 2008
• Up to 5 Gigabits per second!
• 10 times faster than USB 2.0

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Clocking Data

• Both serial and parallel busses transfer data
  using a clock signal that ensures that data is
  sent and received at certain times based on the
  clock speed.
• Without the clock, data transfers would be less
  reliable given the variation in cable length and
  other environmental factors

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Questions?
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Numeric Processingand SpreadSheets
(Excel)Lecture 7, Part II
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• First we thought the computer was a calculator.
  Then we found out how to turn numbers into
  letters with ASCII and we thought it was a
  typewriter. Then we discovered graphics, and we
  thought it was a television. With the World Wide
  Web, weve realized its a brochure.
• -Douglas Adams

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The problem with numbers

• Storage space for numbers in computers is
  predetermined based on the size of the numbers
  specified in the computer program
• Errors can occur!

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Digital Number Representations

• Integers
• infinite discrete subset of the number line
• are represented with a limited range
• Decimal numbers (real numbers)
• infinite and continuous
• are represented with limited range and limited
  precision

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Integer Storage

• All integers between two values (one negative and
  one positive) are stored with exact precision
• The specific values marking the range limits
  depend on the particular computer system being
  used
• If calculations with integers give rise to
  numbers outside the allowable range, we say that
  an integer overflow error has occurred

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Positive Integers
1101



8 4 0
1 13
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Integer Addition in Binary
10010 18 1110
14 100000 32
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Integers in a Finite Machine

• In some current day machines an integer quantity
  is given 16 bits of space.
• This means than when representing numbers as 16
  bit integers, we cannot represent any positive
  integer larger than 216. (65536) or /- 32767
• If we try to represent larger numbers than we
  have bits available to represent them we get an
  Overflow condition

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Real (Decimal) Number Storage

• Real numbers are stored in floating point
  representation
• a sign
• an exponent
• a mantissa (normalized decimal fraction)
• no digits to the left of the decimal
• first digit to the right of the decimal is
  nonzero
• Limited precision because most real numbers have
  an infinite decimal expansion

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Floating-point Numbers
sign-bit
Exponent
Mantissa
0
11111000001111111111111
11111111

• 30 23 22
  0
• MSB LSB

Most Significant Bit
Least Significant Bit
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Example of fractional valuesin Binary
Binary Decimal Fraction Decimal
Value .1 1/2 .5 .01 1/4 .25 .001 1/8 .
125 .0001 1/16 .0625 .00001 1/32 .03125
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Decimal Fraction Factored As... Binary 1/2 1/2
.1 1/4 1/4 .01 3/4 1/2 1/4 .11 1/8 1/8
.001 7/8 1/2 1/4 1/8 .111 3/8 1/4
1/8 .011 1/16 1/16 .0001 3/16 1/8
1/16 .0011 5/16 1/4 1/16 .0101
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Real Number StorageLimited Range and Precision

• There are three categories of numbers left out
  when floating point representation is used
• numbers out of range because their absolute value
  is too large (similar to integer overflow)
• numbers out of range because their absolute value
  is too small (numbers too near zero to be stored
  given the precision available
• numbers whose binary representations require
  either an infinite number of binary digits or
  more binary digits than the bits available

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Limited Range and Precision Some Consequences

• Limited range will invalidate certain
  calculations
• If integers are involved, this can often be
  avoided by switching to real numbers
• For real number calculations, this problem arises
  infrequently and in those cases can sometimes be
  handled by special methods. It is not a common
  occurrence in non-scientific work.
• Limited precision for real numbers is very
  pervasive
• Assume that most decimal calculations will, in
  fact, be in error by a very small amount!
• Evaluate and use computer calculations with this
  in mind

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Real Number StorageLimited Range and Precision
Illustrated
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Demousing Excel
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Risks in Numerical Computing

• Almost all complex computer numerical
  calculations involve roundoff error (limited
  precision error)
• If not monitored and planned for carefully, such
  errors can lead to unexpected and catastrophic
  results
• Arianne 5 Rocket Failure
• Patriot Missile Failure during Gulf War

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Spreadsheets

• Spreadsheets are without doubt the way most users
  do numerical processing.

A B C
If I am changed, redo B4
106 231 111 448
1 2 3 4 5
B1B2B3
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SpreadsheetsBrief History

• First spreadsheets appeared in early 1980s
• Visicalc was the first killer app for Apple
• helped popularize personal computers
• Basic Organization Hasnt Changed
• computations organized on a two-dimensional
  worksheet
• both built-in and user-supplied formulas used to
  facilitate computation

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SpreadsheetsBasic Features

• Worksheet Organization
• rectangular grid of cells
• cells are identified by the row (indicated by an
  integer) and column (indicated by a letter) in
  which they appear
• Entering Data
• one cell is active at a time (called the current
  cell)
• a separate data entry bar is associated with the
  current cell
• text, numerical data, dates, and formulas can be
  entered into the current cell through the entry
  bar

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Worksheet OrganizationIllustrated
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SpreadsheetsBasic Features (contd)

• Formatting Data
• variety of formats depending on the type of data
• data format is associated with the cell and can
  be changed later
• Using Formulas in a Worksheet
• cell addresses (column, row) can be used like
  variable names in formulas
• formulas begin with an or other special symbol
  (like _at_)

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Using Spreadsheet FormulasAn Example
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SpreadsheetsBasic Features (contd)

• Copying (Replicating) Formulas
• formulas can be copied to perform repetitive
  calculations
• especially useful when similar calculations take
  place on a group (block,row, column) of
  contiguous data
• Cell Referencing
• cell references will be adjusted automatically
  when formulas are copied if relative cell
  addressing is used in formulas
• cell references will remain the same if absolute
  cell addressing is used in formulas
• relative cell addressing is the default
  addressing scheme

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Copying Spreadsheet FormulasAn Example
The formula in cell B12 has been copied to cells
C12 and D12. Note how the cell references are
automatically adjusted.
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SpreadsheetsAdditional Features

• Using absolute references and problem parameters
• Using built-in functions
• Using logical functions
• Displaying data in charts
• Spreadsheets as decision support tools

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Spreadsheet ModelsUsing Problem Parameters

• Most spreadsheet models will require
  modifications over time as underlying assumptions
  and important problem values change
• Good spreadsheet design will minimize the danger
  of making errors when updating spreadsheet models
• Problem parameters are important problem values
  that are subject to change over time
• Separating problem parameters, placing them in
  clearly identified cells, then referring to them
  by absolute references in formulas within the
  model makes changing them relatively error-proof

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Spreadsheet ModelsDecision Support

• Modeling problem parameters as clearly identified
  separate entities enables convenient what if
  analysis in spreadsheet models
• What if analysis involves observing modified
  calculations and results when problem parameters
  change. In other words, the model is examined in
  response to questions of the form What if
  changes to ?

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Spreadsheet ModelsUsing Built-in Functions

• Built-in functions act on arguments to produce
  resulting values
• A user of a built-in function need not know all
  the details of how the function does its
  calculation
• The user needs to understand only what input
  arguments are required and what type of result is
  produced
• An extensive library of financial and statistical
  functions adds powerful problem-solving
  capabilities for the average user

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Spreadsheet ModelsUsing Built-in Logical
Functions

• Logical functions allow spreadsheet models to
  make decisions during calculations
• Such processing is called conditional processing
  and is a fundamental property of programming
  languages
• For example, the IF function acts on a logical
  (or Boolean) expression to take one of two
  actions, as shown here

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Spreadsheet ModelsDisplaying Data in Charts

• Graphical display and summary of data is often
  easier to interpret than the raw data itself
• Spreadsheets typically provide several types of
  charts
• bar charts
• pie charts
• 3D Charts

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Bar ChartAn Example
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Pie ChartAn Example
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3D Charts
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Summary

• Integers are stored with limited range real
  numbers (decimals) with limited range and limited
  precision
• Almost all large decimal calculations involve
  round off errors because of limited precision
• Spreadsheets provide powerful, yet easy to use,
  calculation environments
• formulas and relative referencing provide for
  easy calculation extension
• absolute referencing and problem parameters
  enable modeling
• built-in functions (arithmetic and logical)
• displaying data in charts
• decision support tool