Chapter 2
What is the system unit?
A boxlike case that houses the
computer’s main hardware components
What are the different types of system units?
Desktops
Personal Digital
Assistant
Notebook
What’s inside the system unit?
Motherboard (mainboard)- Large printed circuit board
with thousands of electrical circuits
Power supply- Transforms alternating current (AC) from
wall outlets to direct current (DC) needed by the computer
Cooling fan- Keeps the system unit cool
Internal Speaker- Used for beeps when error is
encountered
Drive bays- Housing for the computer’s hard drive,
floppy drive and CD-ROM / DVD-ROM drives
Click N Learn
What’s on the motherboard?
System clock- Synchronizes the computer’s internal
activities
Microprocessor (CPU)- Central processing unit
interprets and carries out instructions given by software
Memory- Enables the computer to retain information
Chipset- A collection of chips that provide the switching
circuitry needed to move data
Input/Output buses- Pathways that allow the
microprocessor to communicate with input and output
devices
Click N Learn
The Motherboard
Microprocessor
Keyboard /
Mouse Ports
Memory Slots
Printer Port
Video Port
AGP Slot
PCI Slots
Chipset
What are the types of CPUs?
Intel
Pentium IV
Pentium III
Advanced
Micro Devices
(AMD)
Pentium MMX
Cyrix
Motorola (Apple)
What are the components of the CPU?
Control unit- Coordinates and controls all parts of
the computer system
Arithmetic-Logic unit- Performs arithmetic or
logical operations
Registers- Stores the most frequently used
instructions and data
Click N Learn
How do CPUs work?
Control Unit- Manages four basic operations
(machine cycle)
Fetch- Gets next program instruction from the computer’s memory
Decode- Figure out what the program is telling the computer to do
Execute- Perform the requested action
Write-back (Store)- Write (store) the results to a register or to memory
Arithmetic-Logic Unit (ALU)- Perform basic
arithmetic or logic operations
Add, Subtract, Multiply, Divide
Compare two items to see which one is larger or
smaller
Intel
Click to
animate.
Click one
time only
How a CPU works
Control unit
Memory
ALU
What determines a CPUs performance?
Data bus width- The number of pathways within the
CPU that transfers data (8, 16, 32, 64)
Word size- The maximum number of bits of data that
the CPU can process at a time (8 bits, 16 bits, 32 bits, 64
bits)
Operations per cycle (clock speed)- The number of
clock cycles per second measured in Megahertz (MHz)
or Gigahertz (GHz)
Specifications:
Clock Speed: 1.0 GHz
System / Front Side Bus Speed: 133 MHz
Level 1 Cache: 16K Instruction + 16K data
Level 2 Cache: 256 KB
What is memory?
A term for a device that enables the
computer to retain (store) information.
What are the types of memory?
Volatile memory (Random Access Memory/RAM;
Cache Memory; Virtual Memory)- Contents of
memory are erased when power supply is turned
off. Also called Temporary storage.
Nonvolatile memory (Read Only Memory/ROM;
Flash Memory)- Contents of memory are not erased
when power is turned off. Also called Permanent
storage.
What is Random Access Memory / RAM?
A type of volatile memory that stores
information temporarily so that it’s available to
the CPU.
What are the different types of RAM?
Dynamic RAM- A memory chip that needs to be
refreshed periodically or it loses its data
 Synchronous DRAM (SDRAM)- Synchronized with
the computer’s system clock
 Rambus DRAM (RDRAM)- Uses fast bus to send
and receive data within one clock cycle. Faster than
SDRAM
 Double Data Rate SDRAM (DDR SDRAM)- A type of
SDRAM that can send and receive data within one
clock cycle.
Kingston
What is a memory module?
A narrow printed circuit board that
holds memory chips
Three types
 Single Inline Memory Module (SIMM)- 30 or
72 pin connectors. Available in 1MB, 4MB,
16MB, and 32MB versions
 Dual Inline Memory Module (DIMM)- 168 or
184 pin connectors. Available in 8MB, 16MB,
32MB, 64MB, 128MB, 256MB, and 512MB
versions
 Rambus Inline Memory Module (RIMM)
Kingston
DIMM
RIMM
NOTEBOOK
DIMM
SIMM
HOW DOES RAM WORK?
CHIPS CONTAIN MEMORY LOCATIONS
CALLED MEMORY ADDRESSES
THE CPU STORES AND RETRIEVES DATA
BY GOING TO THE MEMORY ADDRESSES
Intel
HOW RAM WORKS
CLICK TO BEGIN
ANIMATION
MONITOR
WEB
RAM
KEYBOARD
CPU
What is cache memory?
Primary cache (Level 1 or L1)- Located within the
CPU chip, it is the memory the microprocessor uses to
store frequently used instructions and data.
Secondary cache (Level 2 or L2; Backside Cache)Located near the CPU, it is the memory between the
CPU and RAM
Faster than RAM
What is virtual memory?
Part of the hard disk is reserved as RAM
When RAM modules become full the CPU
accesses the hard disk to store and retrieve
data
Slower than RAM
FULL
What is a chipset?
A collection of chips that work
together
Provides circuitry to move data to
and from the rest of the computer
What are input/output (I/O) buses?
Pathways that enable the CPU to
communicate with input/output devices
Typically the buses contain slots
called expansion slots, in which
expansion cards are inserted
Expansion slots
Expansion card
What are the types of I/O buses?
Industry Standard Architecture (ISA)- Slowest type
of bus
Personal Computer Interface (PCI)- Faster than ISA;
supports plug and play
Accelerated Graphics Port (AGP)- Designed for
video adapters
Universal Serial Bus (USB)- Allows up to 127 devices
to be connected to the computer at one time; supports
plug and play
What’s on the outside of the system unit?
Power switch- Located on the back; turns power on/off
to the computer
Receptacles- Called connectors or ports; Usually
located on the back; Used to plug in peripheral devices,
keyboard, mouse and monitor
Front panel- Contains drive bays, various buttons and
lights
BACK
FRONT
Drive bays
On/off switch
Reset button
Indicator lights
What types of ports do computers have?
Serial port- Data flows in a series of pulses, one after another one
bit at a time; Slow data transfer rate; Modems
Parallel port- Data flows through eight wires allowing the transfer of
eight bits of data simultaneously; Faster than serial port; Printers
PS/2 port (mouse port)- Special serial port to connect mouse
Small Computer System Interface (SCSI)- Found mostly on
MacIntosh computers; A parallel port allowing up to eight devices to
be connected at a time
Universal Serial Bus (USB)- Allows up to 127 devices to be
connected at a time
1394 port (Firewire)- Similar to USB; allows up to 63 devices to be
connected at a time
IrDA port- Use infrared signal; No physical connection
VGA connector- A 15 pin connector used for monitors
Telephone, Network, PC card, and Sound connectors
Types of ports/connectors
What’s the difference between serial and parallel ports?
SERIAL
PARALLEL
How does a computer represent data?
Electronic signals or impulses
Two types of signals
 Analog- Continuous waveform; Examplestalking and computerized gas pumps.
 Digital- On/off electrical states (bit); Exampleslight switches and transistors; Most computers
use digital signals.
Analog
Digital
ON OFF
ON OFF
What are bits and bytes of data?
Bit (Binary digit)- On or off state of electric
current; Basic unit of information; Represented by
1’s and 0’s (binary numbers).
Byte- Eight bits grouped together to represent a
character (Alphabetical letters, numbers and
punctuation symbols); 256 different combinations.
OFF
ON
OR
0
= 1 bit
1
= 1 Byte
OR
0
0
1
1
0
1
0
0
= 1 Byte
0
1
0
0
0
0
0
1
What are character codes?
Numerical data, that computers
use, translated into characters
readable by humans.
 American Standard Code for
Information Interchange (ASCII)- Eight
bits; Used by minicomputers and
personal computers
 Extended Binary Coded Decimal
Interchange Code (EBCDIC)- Eight bits;
Used by mainframe computers
 Unicode- Uses 16 bits; over 65,000
combinations
=4
0
0
1
1
0
1
0
0
=A
0
1
0
0
0
0
0
1
What are kilobits, megabits and gigabits?
Terms that describe units of data
Used for measuring data transfer rate
(bits per second). Example- 56kbps Modem
1000 bits = 1 kilobit (kb)
1,000,000 bits = 1 megabit (mb)
1,000,000,000 bits = 1 gigabit (gb)
What are Kilobytes, Megabytes, Gigabytes
and Terabytes?
Terms that describe units of data
Used to measure data storage. Example- 20 GB
hard drive
8 bits = 1Byte
1024 Bytes = 1 Kilobyte (KB)
1,048,576 Bytes = 1 Megabyte (MB)
1,043,741,824 Bytes = 1 Gigabyte (GB)
1,099,511,627,776 Bytes = 1 Terabyte (TB)
THE
END