Computer Systems by O8u17v


									Computer Systems

   Mr. McCullough
 AP Computer Science
   August 7, 2012
      Quoth the College Board . . .

A working knowledge of the major hardware
 and software components of computer
 systems is necessary for the study of
 computer science as is the importance of
 considering the ethical and social
 implications of computing systems . . .
      Section VI, AP Computer Science

Go to the College Board Website
Major components of a computer
• Central Processing
• Memory
• Peripheral devices
         The central processing unit or

• Locates and executes
  program instructions
• Carries out simple
• Retrieves data from storage
  and input/ output devices
                                The Pentium 4
• Speed measured in Hz

• Fastest Desktop?

• The fastest computer
  in the world
        The price of speed . . .




               Faster than a speeding bullet?
               Um, faster, actually . . .
• To manipulate stored data
  within a computer system,
  we must have a way of
  storing and retrieving it
• Two types:
  – Primary
  – Secondary
                          Primary Storage
• RAM (Random
  Access Memory),
• Data can be accessed
  in any “random” order
• Holds the program
  code and data during
         Primary storage is electronic

• No moving parts
  very fast!
• Volatility
                      Secondary storage
– Includes magnetic
  tape and disks
– More permanent
            More Secondary Storage

                    Magnetic Tape

A Hard Disk Pack        DVDs
                ROM and ROM-BIOS
• Read-Only Memory
• Non-volatile
• BIOS (Basic Input/
  Output System)

                       Loads operating
                       System into RAM
           Some Peripheral Devices

•   Keyboard
•   Monitor
•   Speakers
•   Printer
•   Fax/modem
•   Mouse
•   Microphone
And some more . . .
                     Data Representation
Data can be represented
  in two different forms
• Analog: Represents
  continuously variable
  quantities that can fall
  anywhere on a
• Digital: Can only
  represent a finite
  number of times.
    Digitalization and binary code

• Computers are digital machines
• Bits: fundamental units of information
  – Short for “binary digit”
  – “on” or “off” status
                          Evolution of binary
•   Vacuum tubes
•   Transistors
•   Integrated Circuits
•   Microprocessors
                    Stage I: Vacuum Tubes

                            First electronic

Eniac, one of the world’s
    first computers
     Generation I: Vacuum Tubes

Vacuum tube assembly   The first computer bug.
              Generation II: Transistors

RCA transistor ad,
from Fortune 1953/03
       Generation III: Integrated Circuits

Integrated circuits placed all compon
ents in one chip, drastically reducing         Calculator, 1972
 the size of the circuit and its components.
 Generation IV: The Microprocessor

• For more than 30
  years, since the 1960's,
  the number of
  transistors per unit
  area has been doubling
  every 1.5 years.
• Moore's law, after
  Gordon Moore,

                             The Intel 4004
  How is “on” or “off” represented?

• In RAM: presence or
  absence of electrical charge
• Disk: Magnetic
  arrangement of surface
• CDs and CD-ROMS:
  Microscopic pits
• Fiber optic cable: Pulses of
        Binary representation and int

How many possibilities
can be conveyed?         How about now?
Binary representation and int

        How about now?
Binary representation and int

       How about now?
                          Bits and bytes

• Bits are combined in
  an encoding system to
  represent letters
• 8 bits in a byte
• How many numbers
                                           < p>
  can be represented by
  one byte?
Java and the 4-byte int
      Other “primitive” data types

• double: 8 byte floating
  point number.
• boolean: has only two
  possible values: true
  and false.
• char: 2 bytes, stores a   No offense.
  single character.

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