Discovering
Computers 2010
Living in a Digital World
The System Unit
• The system unit is a case that contains electronic
components of the computer used to process data.
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The System Unit
• The common components found inside the
system unit includes:
Drive bay(s)
Power supply
Sound card
Video card
Processor
Memory
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The System Unit
• The motherboard is the main circuit board of the system
unit.
– It connects all the components of the computer system.
– Contains the processor, expansion slots, memory slots, and
– Also called the system board.
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The System Unit
• What is a chip?
– A small piece of semi-conducting material on which integrated
circuits are etched.
• Integrated circuits contain many microscopic pathways capable of
carrying electrical current.
– One of the most important chips in your
computer is the processor chip.
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Processor
• The processor interprets and carries out the basic
instructions that operate a computer.
– Also called the central processing unit (CPU).
– The processor is made up of two components:
1.
2.
The control unit is the component of the processor that directs and
coordinates most of the operations in the computer.
The arithmetic logic unit (ALU) performs arithmetic, comparison, and
other logical operations.
Processor
Control
Unit
Arithmetic
Logic Unit (ALU)
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Processor
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Processor
• For every instruction, a processor repeats a set of four basic
operations, which comprise a machine cycle.
Step 1. Fetch
Obtain program instruction
or data item from memory
Memory
Step 2.
Decode
Step 4. Store
Translate
instruction into
commands
Write result to memory
Processor
ALU
Step 3. Execute
Control Unit
Carry out command
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Processor
• What is pipelining?
– A technique used by the processor to speed up processing of instructions.
– Processor begins fetching a second instruction before it completes the
machine cycle for the first instruction.
– Results in faster processing.
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Processor
• What is a register?
– A temporary high-speed storage area, located on the
processor, that holds data and instructions.
Stores location
from where instruction
was fetched
Stores
instruction while it is
being decoded
Stores data
while ALU
computes it
Stores results
of calculation
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Processor
• What is the system clock?
– Controls the timing of all computer operations.
– Generates electronic pulses, or ticks, that set the pace for all
components of the system unit and operations.
– The pace of the system clock is called the clock speed or
clock rate.
• Clock speed is currently measure in gigahertz (GHz).
1 GHz = one
billion ticks of system
clock per second
2 GHz = two
billion ticks of system
clock per second
3 GHz = three
billion ticks of system
clock per second
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Processor
• What are dual-core and multi-core processors?
– A dual-core processor is a single chip that contains two
separate processors.
– A multi-core processor is a single chip that contains two or
more separate processors.
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Processor
• The processor generates a lot of
heat that can ruin the chip.
• Keeping things cool…
– A heat sink is a component with
fins that dissipates heat coming
from the processor.
– A heat pipe is a smaller device
used for laptop computers.
– Liquid cooling uses a continuous
flow of fluids to transfer heat
away from components.
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Processor
• The leading manufacturers
of processor chips are
Intel and AMD.
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Processor
• Parallel processing uses multiple processors
simultaneously to execute a single program or task.
– Massive parallel processing systems can involve hundreds or
thousands of processors.
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Data Representation
Analog signals are continuous and vary in
strength and quality
Digital signals are in one of two states: on
or off
• Most computers are digital.
• The binary system uses two unique digits (0 and 1)
• Bits and bytes
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Analog Computers
• Analog computers were also made.
– mechanical, hydraulic and electronic were the three
types of analog computers.
• These computers were used for gun fire control
systems.
• They had limitations, which is the reason
digital computers are widely used today.
• All modern computers are digital.
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Data Representation
• Most computers are digital.
• The binary system uses two unique digits (0 and 1) is used to
represent data and instructions.
– A bit is a binary digit, which is a single 1 or 0.
A computer circuit represents the 0 or
the 1 electronically by the presence or
absence of an electrical charge
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Data Representation
• What is a byte?
– Eight bits grouped together as a unit.
– Provides enough different combinations of 0s and 1s to
represent 256 individual characters.
• Numbers, letters, symbols, etc…
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Data Representation
• ASCII (American Standard
Code for Information
Interchange) is the most
widely used coding scheme
to represent data
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Data Representation
• How is the letter T converted into binary form and back?
Step 1.
Step 2.
The user presses
the capital letter T
(SHIFT+T key) on
the keyboard.
An electronic signal for the
capital letter T is sent to the
system unit.
T
Step 4.
After processing, the binary
code for the capital letter T is
converted to an image, and
displayed on the output device.
Step 3.
The system unit converts the
scan code for the capital letter T
to its ASCII binary code
(01010100) and stores it in
memory for processing.
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Memory
• What is memory?
– Electronic components that store instructions, data and the
results.
– Consists of one or more chips on the motherboard or other
circuit board.
– Each location in memory has an address.
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Memory
• Memory size is measured by the number of bytes it can
store.
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Memory
• The system unit contains two types of memory:
Volatile memory
Nonvolatile memory
Loses its contents when
power is turned off
Does not lose contents
when power is removed
Example includes RAM
Examples include ROM,
flash memory, and
CMOS
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Memory
Step 1. When you start the computer, certain
RAM
Operating system
instructions
Operating system
interface
operating system files are loaded into RAM from
the hard disk. The operating system displays the
user interface on the screen.
Step 2. When you start a Web browser, the
Web browser
instructions
Web browser
window
program’s instructions are loaded into RAM from
the hard disk. The Web browser window is
displayed on the screen.
Step 3. When you start a paint program, the
Paint program
instructions
Paint program
window
program’s instructions are loaded into RAM from
the hard disk. The paint program, along with the
Web Browser and certain operating system
instructions are in RAM. The paint program
window is displayed on the screen.
RAM
Step 4. When you quit a program, such as the
Web browser, its program instructions are
removed from RAM. The Web browser is no
longer displayed on the screen.
Web browser program
instructions are
removed from RAM
Web browser
window is no longer
displayed on
desktop
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Memory
• Three basic types of RAM chips exist:
Dynamic RAM
(DRAM)
Static RAM (SRAM)
Magnetoresistive
RAM (MRAM)
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Memory
• Where does memory reside?
– RAM chips usually reside on a small circuit board called a
memory module.
– Memory slots on the motherboard hold memory modules.
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Memory
• The amount of RAM necessary in a computer
often depends on the types of software you plan
to use
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Figure 4-21
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Memory
• What is a memory cache?
– Helps speed computer processes by storing frequently used
data and instructions.



L1 cache built into
processor
L2 cache slower but
has larger capacity,
built directly on
processor chip
L3 cache is separate
from processor chip on
motherboard.
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Memory
Read-only memory (ROM) refers to memory chips
that permanently store data and instructions
• Firmware
A PROM (programmable read-only memory) chip is a
blank ROM chip that can be written to permanently
• EEPROM can be erased
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Memory
• What is Flash memory?
– Non-volatile memory that can be erased electronically and
rewritten.
– Used with PDAs, smart phones, printers, digital cameras,
automotive devices, etc...
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Memory
• What is CMOS?
Complementary
metal-oxide
semiconductor
memory
Uses battery
power to retain
information when
other power is
turned off
Used in some
RAM chips, flash
memory chips, and
other types of
memory chips
Stores date,
time, and
computer’s
startup
information
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Memory
• Access time is the amount of time it takes the processor
to read items from memory.
– Measured in nanoseconds (ns)
– It takes 1/10 of a second to blink
your eye; a computer can
perform over 10 million
operations in same amount
of time.
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Expansion Slots and Adapter Cards
• An expansion slot is a
socket on the motherboard
that can hold an adapter
card
• An adapter card enhances
functions of a component of
the system unit and/or
provides connections to
peripherals
– Sound card and video card
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Expansion Slots and Adapter Cards
• With Plug and Play, the computer automatically
can configure adapter cards and other peripherals
as you install them
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Expansion Slots and Adapter Cards
• Removable flash memory includes:
– Memory cards, USB flash drives, and PC
Cards/ExpressCard modules
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Ports and Connectors
A port is the point at which a peripheral attaches to
or communicates with a system unit.
A connector joins a cable to a port.
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Ports and Connectors
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Ports and Connectors
• On a notebook computer, the ports are on the
back, front, and/or sides
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Ports and Connectors
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Ports and Connectors
• A USB port can connect up to 127 different peripherals
together with a single connector.
– You can attach multiple peripherals using a single USB port with
a USB hub.
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Ports and Connectors
• Other types of ports include:
Firewire
port
Bluetooth
port
SCSI port
eSATA
port
IrDA port
Serial port
MIDI port
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Ports and Connectors
A Bluetooth wireless port
adapter converts a USB port into
a Bluetooth port
A smart phone might
communicate with a notebook
computer using an IrDA port
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Buses
• What is a bus?
– Channels that allow all devices
connected to the computer to
communicate with each other.
– The system bus connects the
processor to RAM memory.
– The bus width determines the
number of bits that can be
transmitted at one time.
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Buses
• Expansion slots connect to expansion buses.
• Common types of expansion buses include:
PCI bus
PCI Express
bus
USB and
FireWire bus
Accelerated
Graphics Port
PC Card bus
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Bays
• A bay is an opening
inside the system unit in
which you can install
additional equipment.
– A drive bay typically
holds disk drives.
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Power Supply
The power supply converts the wall
outlet AC power into DC power
Some external peripherals have an AC
adapter, which is an external power
supply
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Quote of the Day
Change is inevitable …
Except from a vending machine.
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