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Input/Output Systems and Secondary Memory

Lecture 7

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

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

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

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

Memory Hierarchy I

Memory Hierarchy II

Flash Memory

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

Magnetic Tape

- stores data represented by magnetized particles

in linear tracks - magnetized clusters or domains are aligned to

represent binary codes

Longitudinal (9-track)

Magnetic Tape had a density of 6250 bits per inch

Tape Drives in action1950s-80s

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

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

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

Floppy / Hard Disks

Hard Disk Drive

Floppy Diskfits in your shirt pocket !

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

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)

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

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

SanDisk Flash Card

One Gigabyte on a chip...and growing!

The future disk technology

- Looks like a hard drive storage unit but there

are no moving parts inside.

Output Peripherals

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

CRT technology

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

LCDs, How do they work?

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

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

Input Peripherals

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

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)

Parallel / Serial Bus

Flat Parallel Computer Cable

Serial Computer Cable

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

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

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

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

USB 3.0!

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

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

Questions?

Numeric Processingand SpreadSheets

(Excel)Lecture 7, Part II

- 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

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!

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

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

Positive Integers

1101

8 4 0

1 13

Integer Addition in Binary

10010 18 1110

14 100000 32

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

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

Floating-point Numbers

sign-bit

Exponent

Mantissa

0

11111000001111111111111

11111111

- 30 23 22

0 - MSB LSB

Most Significant Bit

Least Significant Bit

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

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

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

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

Real Number StorageLimited Range and Precision

Illustrated

Demousing Excel

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

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

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

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

Worksheet OrganizationIllustrated

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_)

Using Spreadsheet FormulasAn Example

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

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.

SpreadsheetsAdditional Features

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

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

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 ?

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

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

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

Bar ChartAn Example

Pie ChartAn Example

3D Charts

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