Lesson 3

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Lesson 3 How a Computer Processes Data
Unit 1 Computer Basics

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Objectives

• Identify computer system components.
• Explain how the CPU works.
• Differentiate between RAM and ROM.
• Describe how data is represented.

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Computer System Components

• A computer system requires many components to do
  its job
• It requires some device or method to input data
  so it can be processed.
• It requires circuits and programs in order to
  process the data.
• It needs some type of output device to give the
  result of its processing to the user.
• It needs some mechanism for storing data.

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Common System Components
This figure shows several devices that are common
com-ponents of a com-puter system.
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System Motherboard

• Inside the case of a modern PC is the
  motherboard, which contains the electronic
  circuitry of the computer.
• Components found on the motherboard include
• The primary processing chip (CPU).
• The memory chips.
• Expansion slots for system interface cards.
• Ports for connecting external devices.
• BIOS chips that control system start-up.
• The circuitry that enables all of these
  components to communicate.

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Example of a Motherboard
This figure shows the devices inside a PC case,
including the motherboard, the power supply, and
some storage devices.
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The Central Processing Unit

• The CPU is the brains of a computer system.
• The CPU is housed on a silicon chip that contains
  millions of switches and circuits.
• The CPU has two primary sections
• Arithmetic/Logic Unit (ALU)
• This section performs arithmetic and logical
  operations.
• Control Unit
• This section is the boss of the CPU and
  coordinates all activity within the CPU. It uses
  programming instructions to control what actions
  the CPU performs and when it performs them.

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A CPU Chip
This figure shows a CPU chip for a small
computer. The CPU determines which of the
millions of switches that it contains should be
turned on or off by processing program statements
that tell it what to do.
Computer programs are written in programming
languages, and each program statement causes one
or more actions to occur in the CPU.
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Computer Memory

• Data being processed by a CPU is stored in system
  memory.
• Memory consists of addressable locations within
  the machine that the computer can access
  directly.
• Data stored in memory is not permanent. If the
  power fails, everything in memory is lost.
• Data must be stored on a disk or some other
  device when not being processed so it is not lost
  each time the computer shuts down.

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Types of Memory

• RAM Random Access Memory
• This is short-term memory where data is processed
  while a program is running.
• Data stored here can be accessed and modified as
  needed.
• This type of memory loses any data it holds if
  the computer is shut down.
• ROM Read-Only Memory
• ROM is memory placed on the motherboard by the
  manufacturer and contains instructions that tell
  the computer how to start itself.
• This data cannot be accessed or modified by
  application programs.
• The contents of this memory are not lost when the
  computer is shut down.

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The Instruction and Execution Cycles
This figure illustrates the basic cycle involved
in process-ing a program statement. This process
is called the instruction cycle. The amount of
time required to complete the instruction cycle
is referred to as the execution cycle.
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The Machine Cycle
The instruction cycle and one or more exe-cution
cycles create a machine cycle, as shown here.
Machine cycles are measured in microseconds, and
the faster your computer can process machine
cycles, the faster it can process data.
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Computer System Controllers

• A PC motherboard also contains several
  controllers.
• Controllers are devices that control the transfer
  of data between the computer and peripheral
  devices.
• Common peripheral devices include a mouse, a
  monitor, a printer, a keyboard, and so on.
• Controllers are usually found on a single chip
  which can handle all usual devices.

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Ports and Expansion Slots

• Serial and parallel ports are used to connect
  peripheral devices to the computer circuitry.
• Serial devices (mice/monitors) transmit data one
  bit at a time.
• Parallel devices (printers) transmit data several
  bits at time.
• USB is a newer, high-speed method of connecting
  devices and is beginning to replace serial and
  parallel ports.
• Expansion slots are electrical connections in the
  motherboard that can accept circuit cards to
  perform specific functions.
• These are commonly used to plug in sound cards,
  video cards, scanners, and other devices.

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A Typical Expansion Card
It has electrical prongs along the bottom to plug
into the expansion slot and make an electrical
connection to the main board.
This port sticks out of the back of the PC case
and is used to attach the device that this card
controls.
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Data Representation

• Data is stored in a computer in binary format as
  a series of 1s and 0s.
• Computers use standardized coding systems (such
  as ASCII) to determine what character or number
  is represented by what series of binary digits.
• Data is stored in a series of 8-bit combinations
  called a byte.
• Every letter, number, punctuation mark, or symbol
  has its own unique combination of ones and zeros.

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Summary

• Just about all computers perform the same general
  options input, processing, output, and storage.
• Input, output, and processing devices grouped
  together represent a computer system.
• The motherboard is the center of all processing.
• The motherboard contains the CPU, memory, and
  basic controllers for the system.

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Summary (continued)

• The motherboard also contains ports and expansion
  slots.
• The central processing unit is the brains of the
  computer.
• The computer is given instructions through
  computer programs.
• The CPU has two main sectionsthe arithmetic
  logic unit and the control unit.

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Summary (continued)

• All calculations and comparisons take place in
  the ALU.
• The control unit coordinates the CPU activities.
• The motherboard contains different types of
  memory.
• Random access memory is volatile and is used to
  store instructions, data, and information
  temporarily.

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Summary (continued)

• Read-only memory is nonvolatile and is used to
  store instructions, data, and information
  temporarily.
• The machine cycle is made up of the instruction
  cycle and the execution cycle.
• A controller is used to control the transfer of
  data between the computer and peripheral devices.
• Peripheral devices are connected to the computer
  through serial and parallel ports.

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Summary (continued)

• The Universal Serial Bus is a new standard
  expected to replace serial and parallel ports.
• Expansion boards are used to connect specialized
  peripheral devices or to add more memory to the
  computer.
• The ASCII code is a standard code used to
  represent the alphabet, numbers, symbols, and
  punctuation marks.