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Module 5. Hardware. What Computers Do. Process Information. Produce Output. Receive Input. Store Information. 4 Primary Components of a Computer. Secondary - hard disks - removable disks - CDs - tapes. Primary - memory - RAM - ROM. Storage Devices. Input Devices. Processing.

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Module 5

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Module 5 l.jpg

Module 5


What computers do l.jpg

What Computers Do

Process Information

Produce Output

Receive Input

Store Information

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4 Primary Components of a Computer


- hard disks

- removable disks

- CDs

- tapes


- memory



Storage Devices

Input Devices


Output Devices

- keyboard

- mouse

- scanner

- digital camera

- touchpad

  • CPU

  • Control Unit

  • Arithmetic & Logic Unit

- monitor

- printer

- speakers

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Processing - CPU

  • “Central Processing Unit”


    • evolution of processors

  • the “brains” of the computer, where calculations take place

  • two parts:

    • ALU - Arithmetic Logic Unit

      • electronic circuitry that does all arithmetic and logic operations

    • Control Unit

      • circuitry that directs all other parts of the computer

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Input Devices

  • accept input from the outside world.

  • most common is the keyboard, followed by the mouse

  • sends signals to the computer, telling it what you’ve “told” it

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Output Devices

  • sends output to the outside world

  • converts and displays the computer’s internal bit patterns to a format that humans can understand

  • Main output devices are

    • monitors for immediate visual output

    • printers for permanent paper output

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Screen Output

  • A monitor or video display terminal (VDT) displays characters, graphics, photographic images, animation and video.

    • Video adapter—connects the monitor to the computer

    • VRAM or video memory—a special portion of RAM to hold video images (the more video memory, the more detail of a picture displayed)

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Screen Talk

  • Monitor size - measured as a diagonal line across the screen.

  • Pixels(or picture element) - tiny dots that compose a picture

  • Resolution- the number of pixels displayed on the screen (the higher the resolution, the closer together the dots)

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Image Quality

  • Image quality is affected by resolution and color depth (or bit depth)

  • Color depth refers to the number of different colors a monitor displays at the same time

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4-bit depth

1-bit depth

8-bit depth

16-bit depth

Examples of Color Depth

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Paper Output

  • Printers produce paper output or hard copy

  • 2 kinds of printers:

    • Impact printers

    • Non-impact printers

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Impact Printers

  • Line printer

    • Used by mainframes to produce massive printouts

    • Limited to printing characters

  • Dot matrix printer

    • Images created by a matrix of tiny dots

    • Low print quality

    • Low cost

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Non-impact Printers

  • A laser beam reflected off a rotating drum to create patterns of electrical charges

  • Faster and more expensive than dot matrix printer

  • High-resolution output

Laser Printer

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More on Non-impact Printers

  • Sprays ink onto paper to produce printed text and graphic images

  • Prints fewer pages/minute than laser printer

  • High-quality color costing less than laser printer

Ink-jet Printer

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Storage devices

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Storage/Memory Devices

  • Divided into two groups:

    • Primary storage

      • usually a temporary storage for the data and programs currently in operation or currently being accessed.

      • it’s fastest and most expensive

    • Secondary storage

      • long-term storage locations

      • cheap but slower than primary memory

      • some are portable/removable

      • larger capacity than primary memory

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Primary Storage - RAM

  • RAM: Random Access Memory

  • very fast - access times < 1 billionth of a second – in nanoseconds

  • volatile storage - once the computer is turned off, everything is lost

  • this is where data and programs currently being used reside

    • a document that has not yet been “saved” is in RAM and will be lost if the computer freezes or the power goes off

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Primary Storage - ROM

  • ROM = Read Only Memory

  • permanent memory (doesn’t disappear if the computer is turned off)

  • normally holds the data/programs needed to start (“boot up”) the computer

  • typically, cannot be altered except by physically changing the chip



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Secondary Storage

  • Secondary storage devices are computer peripherals capable of performing both input and output functions

  • Information is stored semi-permanently on tape and disk drives

  • Examples of storage devices

    • Magnetic tapes and disks

    • Zip, Jaz and SuperDisks

    • Optical disks

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Secondary storage - Magnetic Tape

  • Magnetic tapes

    • Sequential access

    • Can store large amounts of information in a small space at a relatively low cost

    • Limitation: sequential access

    • Used mainly for backup purposes

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Magnetic Media

  • Magnetic drives

    • Random access

    • Floppy disks for inexpensive, portable storage

    • Hard disks are typically non-removable, rigid disks that spin continuously and rapidly thus providing much faster access than a floppy disk.

    • Removable media (Zip & Jaz disks) provide high-capacity portable storage.

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Hard Disk

  • magnetic storage

  • data is saved until something is written over it (or it gets damaged somehow)

  • data saved on “platters” and read with a “head”

  • platters spin at 3600-7200RPM

    • head can move to center and back to edge about 50 times per second

    • platters divided into “tracks” and “sectors” to make it easier to retrieve data.

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Optical Media

  • Not as fast as magnetic hard disks

  • Massive storage capacity and reliability

Optical disk drive uses laser beams to read and write bits of information on the disk surface.

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Types of Optical Media

  • CD-ROM drives are optical drives that read CD-ROMs.

  • CD-R are WORM media (write-once, read many). Hold about 700megabytes of info

  • CD-RWcan read CD-ROMs and write (onto CD-R), erase and rewrite data onto CD-RW disks.

  • DVD(digital video disks) store & distribute all kinds of data. They hold between 3.8 and 17 gigabytes of information.

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Solid-state Storage Devices

  • Flash memory is an erasable memory chip.

    • Compact alternative

    • No moving parts

    • Designed for specific applications such as storing pictures in digital cameras

    • Likely to eventually replace disk and tape storage

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The microprocessor that makes up your personal computer’s central processing unit, or CPU, is the ultimate computer brain, messenger, ringmaster and boss. All the other components—RAM, disk drives, the monitor— exist only to bridge the gap between you and the processor.

Ron White, in How Computers Work

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  • The CPU:

    • interprets and executes instructions

    • performs arithmetic and logical data manipulations

    • communicates with the other parts of the computer system.

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  • The CPU is a complex collection of electronic circuits.

    • When all of those circuits are built into a single silicon chip, the chip is referred to as amicroprocessor.

    • The circuit board that contains a computer’s CPU is called the motherboard or system board.


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CPU Speed

  • A computer’s speed is determined in part by the speed of its internal clock

    • The clock is a timing device that produces electrical pulses to synchronize the computer’s operations.

    • A computer’s clock speed is measured in units called megahertz (MHz), for millions of clock cycles per second

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CPU Speed

  • Parallel processingplaces multiple processors in a computer.

  • Most supercomputers have multiple processors that divide jobs into pieces and work in parallel on the pieces.

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Ports and Slots

Tying things together

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Ports and Slots

  • The system or motherboard includes several standard ports:

    • Serial Portfor attaching devices that send/receive messages one bit at a time (modems)

    • Parallel Portfor attaching devices that send/receive bits in groups (printers)

    • Keyboard/Mouse Portfor attaching a keyboard and a mouse

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More on Ports and Slots

  • Other ports are typically included on expansion boards rather than the system board:

    • Video Portused to plug in a color monitor into the video board

    • Microphone, speaker, headphone, MIDI ports used to attach sound equipment

    • SCSI port allows several peripherals to be strung together and attached to a single port

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Expansion Made Easy

With the open architecture of the PC and the introduction of new interfaces, you can now hot swap devices.

  • USB(Universal Serial Bus) transmits a hundred times faster than a PC serial port

  • Firewire (IEEE 1394) can move data between devices at 400 or more megabits per second

    • high speed makes it ideal for data-intensive work like digital video

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Bits and Bytes

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Information comes in many forms

Computers store information in digital form

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Bit Basics

  • A bit (binary digit)

    • is the smallest unit of information

    • can have two values: 1 or 0

    • can represent numbers, codes, orinstructions


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Bits as Numbers

  • Each switch can be used to store a tiny amount of information, such as:

    • An answer to a yes/no question

    • A signal to turn on a light

  • Larger chunks of information are stored by grouping bits as units

    • 8 bits (byte) = 256 different messages

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Bits As Codes

ASCII – American Standard Code for Information Interchange

Most widely used code, represents each character as a unique 8-bit code.

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Bits as Instruction

  • The computer stores instructions as collections of bits. For instance, 01101010 might instruct the computer to add two numbers.

  • Other bit instructions might include where to find numbers stored in memory or where to store them.

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Kilobyte (KB)

Megabytes (MB)

Gigabytes (GB)

Terabytes (TB)

= 8 bits

≈1 Thousand Bytes

≈1 Million Bytes

≈1 Billion Bytes

≈1 Trillion Bytes

Bits, Bytes, and Buzzwords

Terms used to describe file size or memory size:

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The logic machine

  • How do we build a computer that doesn’t need to be rewired each time we want to perform a different task?

  • Connect the components in such a way that the program itself controls the “rewiring” by signaling the hardware to switch the components on and off in the proper sequence

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Logic Gates

  • Using switches, we can reproduce the logical operators

    • AND

    • OR

    • NOT

  • 0 = false = off

  • 1 = true = on

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AND is written like a multiply

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OR is written like an


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NOT is written with an ’ after the letter

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Simple Truth Table

“if both P and Q are the same, then the result is true”

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Example: check to see if P and Q are equal

  • Step 1: build Truth Table

    • The truth table for “P and Q are equal” looks like:

P = 0, Q = 0 they are equal so result is true (1)

P = 1, Q = 1 they are equal, so result is true (1)

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Step 2:

  • Build an AND statement for each line where Result = 1

the ’ means NOT… so P’ means that P is off/0

P’ AND Q’ = P’Q’


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Step 3:

  • Join each line with OR-statements

result=P’Q’ + PQ

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Example 2:

Step 1: Build Truth Table … already done for us

Step 2: Build equation terms using ANDs

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Step 3: Build equation by joining terms from step 2 with ORs

S = P’Q’ + PQ’ + PQ

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Drawing circuits

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One output

Two inputs

  • AND=*=

  • OR=+=

  • NOT= ’ =

Two inputs

One output

One output

One input

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Gates to switches

  • Logical gates can be converted to physical switches that operate exactly as expected

  • We can combine gates to act like our statements from the truth tables since we have a gate for each of AND, OR, NOT

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Building Circuits

  • We build the circuit in the exact same order as we build the equation

    • figure out the inputs

    • do all the NOTs

    • next all the ANDS

    • lastly all the ORs

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Result = PQ + P’Q’




Step A: Inputs

One input (light switch) for each letter in the equation

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Result = PQ + P’Q’

Step B: NOTs





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Step C: ANDs

Result = PQ + P’Q’

Remember AND is the same as a multiply

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PQ + P’Q’


Step D: ORs

Result = PQ + P’Q’

Remember OR is the same as addition



The light will light up when the inputs are both the same, as described in the truth table

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Example3 inputs, light-up if exactly 2 inputs are true

Step 1: Build Truth Table

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Step 2: build terms with ANDs (where result is true)

Step 3: Build equation by joining terms with ORs

result = X’YZ + XY’Z + XYZ’

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Step 4: Build circuit

result = X’YZ + XY’Z + XYZ’

Step A: Inputs

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result = X’YZ + XY’Z + XYZ’

Step B: NOTs

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result = X’YZ + XY’Z + XYZ’

Step C: ANDs


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result = X’YZ + XY’Z + XYZ’





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result = X’YZ + XY’Z + XYZ’





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Using Loggo to combine gates

  • Go to the class homepage and look for the Loggoapplet in the Miscellaneous section

  • Try implementing different equations to see if they match the truth tables

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Corresponding Readings

  • Chapter 2

  • Chapter 3

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To Know – Module 5

  • Vocabulary/definitions

  • Truth tables / circuits

    • From a description, write truth table

    • From truth table, write equation

    • From equation, build circuit

  • Login