Transcript Module 5

Module 5


What Computers Do

Process Information Receive Input Store Information Produce Output

4 Primary Components of a Computer


- memory - RAM - ROM Input Devices Storage Devices Processing


- hard disks - removable disks - CDs - tapes Output Devices - keyboard - mouse - scanner - digital camera - touchpad -CPU -Control Unit -Arithmetic & Logic Unit - monitor - printer - speakers

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

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

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

Screen Output

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

 

Video adapter

the computer —connects the monitor to


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

Screen Talk

Monitor size

- measured as a diagonal line across the screen.


(or picture element) - tiny dots that compose a picture 


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

Image Quality

 Image quality is affected by resolution depth and color (or bit depth)  Color depth refers to the number of different colors a monitor displays at the same time

Examples of Color Depth

4-bit depth 1-bit depth 8-bit depth 16-bit depth

Paper Output

 Printers produce paper output or hard copy  2 kinds of printers:  Impact printers  Non-impact printers

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

Non-impact Printers

Laser Printer

 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

More on Non-impact Printers

Ink-jet Printer

 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

Storage devices

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

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

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


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

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

Magnetic Media

 Magnetic drives   Random access

Floppy disks

storage for inexpensive, portable  

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.

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.

Optical Media

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

 Not as fast as magnetic hard disks  Massive storage capacity and reliability

Types of Optical Media


drives are optical drives that






media (write-once, read many). Hold about 700megabytes of info 


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


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

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



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


The CPU:

 interprets and executes instructions  performs arithmetic and logical data manipulations  communicates with the other parts of the computer system.


 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 a



 The circuit board that contains a computer’s CPU is called the



system board


motherboard CPU

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

CPU Speed

Parallel processing

places multiple processors in a computer.

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

Ports and Slots

Tying things together

Ports and Slots

 The system or motherboard includes several standard ports: 

Serial Port

for attaching devices that send/receive messages one bit at a time (modems) 

Parallel Port

for attaching devices that send/receive bits in groups (printers) 

Keyboard/Mouse Port

and a mouse for attaching a keyboard

More on Ports and Slots

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

Video Port

used 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

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

Bits and Bytes


Information comes in many forms Text Pictures 2 1 3 Numbers Sounds Computers store information in digital form

Bit Basics

On/off  A bit (binary digit)  is the smallest unit of information  can have two values:




 can represent

numbers, codes,



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

Bits As Codes


– American Standard Code for Information Interchange Most widely used code, represents each character as a unique 8-bit code.

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.

Bits, Bytes, and Buzzwords

Terms used to describe file size or memory size:      Byte Kilobyte (KB) Megabytes (MB) Gigabytes (GB) Terabytes (TB) = 8 bits ≈ 1 Thousand Bytes ≈ 1 Million Bytes ≈ 1 Billion Bytes ≈ 1 Trillion Bytes

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

Logic Gates

 Using switches, we can reproduce the logical operators   AND OR  NOT  0 = false = off  1 = true = on



0 0 1 1


0 1 0 1

PQ 0 0 0 1

AND is written like a multiply



0 0 1 1


0 1 0 1

P+Q 0 1 1 1

OR is written like an addition



0 1

P’ 1 0

NOT is written with an ’ after the letter

Simple Truth Table


0 0 1 1 0 1 0 1

Q PQ + P’Q’ (result)

1 0 0 1 “if both P and Q are the same, then the result is true”

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

0 1

1 Q 0

1 0

1 Result 1 0 0 1

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

Step 2:

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

P 0 1 Q 0 1 Result 1 1

the ’ means NOT… so P’ means that P is off/0 P’ AND Q’ = P’Q’ P AND Q = PQ

Step 3:

 Join each line with OR-statements P’Q’



result = P’Q’ + PQ

Example 2:

Step 1: Build Truth Table … already done for us


0 0

1 P’Q’

0 1


1 1 0 1

1 1 PQ’ PQ

Step 2: Build equation terms using ANDs


0 0 1 1


0 1 0 1

S 1 0 1 1 P’Q’ PQ’ PQ

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

S = P’Q’ + PQ’ + PQ

Drawing circuits

 AND =  OR =  NOT = *


Two inputs = Two inputs + = One input ’ = One output One output One output

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

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

Result = PQ + P’Q’


Step A: Inputs P Q One input (light switch) for each letter in the equation

Step B: NOTs Result = PQ + P’Q’ P



Q P’ Q’

Result = PQ + P’Q’ Step C: ANDs P Q

P Q P’ Q’ PQ P’Q’

Remember AND is the same as a multiply

Step D: ORs Result = PQ + P’Q’ P Q Remember OR is the same as addition

PQ P’Q’ PQ + P’Q’

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


3 inputs, light-up if exactly 2 inputs are true Step 1: Build Truth Table


0 0 0 0 1 1 1 1


0 0 1 1 0 0 1 1


0 1 0 1 0 1 0 1

Result 0 0 0 1 0 1 1 0

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







Result 0

0 0 0 1 1 0

0 0

0 1 1 0 1 0

1 0

X’YZ 1 1 0 1 1 0

1 1

XY’Z XYZ’ 1 1 1


Step 3: Build equation by joining terms with ORs result = X’YZ + XY’Z + XYZ’

Step 4: Build circuit result = X’YZ + XY’Z + XYZ’ Step A: Inputs X Y Z

Step B: NOTs result = X’YZ + XY’Z + XYZ’ X X’ Y Y’ Z Z’

Step C: ANDs result = X’YZ + XY’Z + XYZ’ X X’ Y X’Y Z X’YZ Y Y’ X Z Y X XY’ Z Z’ XY XY’Z XYZ’

X Y Z result = X’YZ + XY’Z + XYZ’


X Y Z result = X’YZ + XY’Z + XYZ’ X’YZ




Using Loggo to combine gates

 Go to the class homepage and look for the


applet in the Miscellaneous section  Try implementing different equations to see if they match the truth tables

Corresponding Readings

 Chapter 2  Chapter 3

To Know – Module 5

 Vocabulary/definitions  Truth tables / circuits  From a description, write truth table  From truth table, write equation  From equation, build circuit