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1. Chapter 2
The Components of the
System Unit

2. Chapter Objectives
Identify chips, adapter cards, and other
components in system unit
Identify chips, adapter cards, and other
components in system unit
Describe the components of a processor and how
they complete a machine cycle
Describe the components of a processor and how
they complete a machine cycle
Identify characteristics of various personalIdentify characteristics of various personal
Describe the types of expansion slots and
adapter cards
Describe the types of expansion slots and
adapter cards
Explain the differences among a serial port, a parallel
port, a USB port, a FireWire port, and other ports
Explain the differences among a serial port, a parallel
port, a USB port, a FireWire port, and other portsIdentify characteristics of various personal
computer processors on the market today
Identify characteristics of various personal
computer processors on the market today
Define a bit and describe how a series of bits
represents data
Define a bit and describe how a series of bits
represents data
Differentiate among the various
types of memory
Differentiate among the various
types of memory
Describe how buses contribute to a
computer’s processing speed
Describe how buses contribute to a
computer’s processing speed
Identify components in mobile computers
and mobile devices
Identify components in mobile computers
and mobile devices

3. The System Unit
What is the system unit?
Case that contains
electronic components
of the computer used
to process data
Also known asAlso known as
chassis

4. Learning Outcome
Successful students will be able to:
Describe the characteristics of computer hardware
devices and explain their functionalities.

5. The System Unit
What are common components inside the system
unit?
Memory
Adapter cards
Sound card
power supply drive bays
processor
Processor
Sound card
Video card
Ports
Drive bays
Power supply
ports memory
sound card
video card

6. The System Unit
What is the motherboard?
Main circuit
board in system
unit
Contains adapter
cards, processorcards, processor
chips, and
memory chips
Also called
system board

7. The System Unit
What is a chip?
Small piece of semi-conducting material on which
integrated circuits are etched
Integrated circuits contain many microscopic pathways
capable of carrying electrical current – can contain
millions of elements: resistors, capacitors, transistors,…
p. 186
millions of elements: resistors, capacitors, transistors,…
Chips are packaged so they can be attached to a
circuit board

8. ProcessorProcessor
ControlControl
UnitUnit
ArithmeticArithmetic
Logic Unit (ALU)Logic Unit (ALU)
ArithmeticArithmetic
Logic Unit (ALU)Logic Unit (ALU)
Processor
What is the central processing unit (CPU)?
Interprets and carries
out basic instructions
that operate a computer
InstructionsInstructions
DataData
InformationInformation
ControlControl
UnitUnit
Control unit directs and
coordinates operations in
computer
p. 187 Fig. 4-4
InputInput
DevicesDevices
StorageStorage
DevicesDevices
OutputOutput
DevicesDevicesMemoryMemoryDataData InformationInformation
InstructionsInstructions
DataData
InformationInformation
InformationInformationcomputer
Arithmetic logic unit
(ALU) performs
arithmetic, comparison,
and logical operations
Also called the processor

9. Processor
What is a machine cycle?
Step 1. Fetch
Obtain program instruction
or data item from memory
Four operations of the CPU comprise a machine cycle
Processor
Control Unit
Memory
ALU
Step 2.
Decode
Translate
instruction into
commands
Step 4. Store
Write result to memory
Step 3. Execute
Carry out command

10. Processor
What is pipelining?
CPU begins fetching second instruction before
completing machine cycle for first instruction
Results in faster processing

11. Stores locationStores location
from where instructionfrom where instruction
Processor
What is a register?
Temporary high-speed storage area that holds
data and instructions
from where instructionfrom where instruction
was fetchedwas fetched
StoresStores
instruction while it isinstruction while it is
being decodedbeing decoded
Stores dataStores data
while ALUwhile ALU
computes itcomputes it
Stores resultsStores results
of calculationof calculation

12. Processor
What is the system clock?
Controls timing of all computer operations
Generates regular electronic pulses, or ticks, that set
operating pace of components of system unit
Each tickEach tick
is ais a
clock cycleclock cycle
Pace of systemPace of system
clock isclock is clock speedclock speed
Most clock speeds areMost clock speeds are
in the gigahertz (GHz)in the gigahertz (GHz)
range (1 GHz = onerange (1 GHz = one
billion ticks of systembillion ticks of system
clock per second)clock per second)
Processor speed canProcessor speed can
also be measured inalso be measured in
mmillions ofillions of iinstructionsnstructions
pperer ssecondecond (MIPS)(MIPS)

13. Processor
Comparison of some of the
more widely used
processors

14. Quick Quiz
1) What is the system unit?
Answer:
A case that contains electronic components of the computer
used to process data
Answer:
Many microscopic pathways capable of carrying electrical
2) What does an integrated circuit contain?
Many microscopic pathways capable of carrying electrical
current
Answer: The control unit is the component of the processor
that directs and coordinates most computer operations; the
arithmetic logic unit is the component that performs
arithmetic and comparison operations.
3) How is the control unit different from the
arithmetic logic unit?

15. Processor
What are heat sinks, heat pipes,
and liquid cooling?
Heat sink —small ceramic or metal component
with fins – absorbs & disperses heat produced
by electrical components
Heat pipe —smaller
Besides computer’s main fan,
today’s processors require
additional cooling
Heat pipe e—smaller
device for notebook
computers
Liquid cooling —uses a
continuous flow of fluids (water,
glycol,..) to transfer heat away
from processor to a radiator type
grill and returns the cooled fluid
to the processor

16. Processor
Mobile computers & devices often have Low
Voltage or Ultra Low Voltage (UVL) processors
Have such low power demands that they do not
require additional cooling.

17. Processor
What is parallel processing?
Control ProcessorControl Processor
Processor 1Processor 1 Processor 2Processor 2 Processor 3Processor 3 Processor 4Processor 4
Using multiple
processors
simultaneously to
execute a program
faster MemoryMemory MemoryMemory MemoryMemory MemoryMemoryfaster
Requires special
software to divide
problem and bring
results together

18. Parallel Processing
Single problem divided into portions
Multiple processors work on their assigned
portions of the problem at the same time
Some PC use dual-core or multi-core processors
Others have two or more separate processorsOthers have two or more separate processors
chips.
Massively parallel processing
large scale parallel processing
involves hundreds or thousands of processors.
Used by supercomputers – AI & weather forecasting
applications.

19. Data Representation
How do computers represent data?
Recognize only two discrete
states: on or off
Use a binary system to
Most computers are digital
Use a binary system to
recognize two states
Use Number system with two
unique digits: 0 and 1, called
bits (short for binary digits)

20. Data Representation
Computers – electronic devices powered by
electricity – has only two states: ON and OFF
The digit 0 represents the electronic state OFF:
absence of electronic charge
The digit 1 represents the electronic state ON:
presence of electronic charge
The digit 1 represents the electronic state ON:
presence of electronic charge
The binary system is a number system that has
just two unique digits, 0 and 1, called bit.
A bit (is not very informative) is the smallest unit of
data the computer can process.

21. 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
UppercaseUppercase
and lowercase
letters
Punctuation
marks
Other

22. Data Representation
What are three popular coding systems to represent data?
ASCII - American Standard Code for Information Interchange
- Used in PCs & servers
EBCDIC - Extended Binary Coded Decimal Interchange Code
- Used primarily on mainframe & supercomputers
(both coding schemes sufficient for English & Western Europe languages
but not for Asian, using different alphabets)
Unicode - 16-bit coding scheme capable of representing all
world’s languages
- implemented in Windows Vista, XP, Mac OS & Linux
ASCII Symbol EBCDIC
00110000 0 11110000
00110001 1 11110001
00110010 2 11110010
00110011 3 11110011

23. Data Representation
How is a letter converted to binary form and back?
Step 1.
The user
presses the
capital letter D
(shift+D key)
on the
keyboard.
Step 2.
An electronic signal for
the capital letter D is
sent to the system unit.
Step 3.
The signal for the capital
letter D is converted to its
ASCII binary code
(01000100) and is stored in
memory for processing.
Step 4.
After processing, the
binary code for the capital
letter D is converted to an
image, and displayed on
the output device.

24. Quick Quiz
1) What is a dual-core processor?
Answer: A single chip that contains two separate processors
2) How are analog signals different from digital
signals?
Answer:
Analog uses continuous (wave form) signals that vary in
strength and quality; digital signals, which are used by most
computers, recognize only two discrete states: on and off
signals?

25. Memory
What is memory?
Electronic components that store:
- instructions waiting to be executed,
- data needed by those instructions, and
- the results of processed data (information)
Consists of one or more chips on motherboard or other
circuit board
Each byte stored in memory at unique location called
an address

26. Memory
What is memory? (cont.)
A byte (a character) – 8 bits - is the basic storage unit in
memory
Each byte resides temporarily in a location in memory
that has an address – a unique number that identifies the
location of a byte in memorylocation of a byte in memory
To access data or instruction in memory, computer
references the addresses that contain bytes of data

27. Memory
How is memory measured?
Term Abbreviation Approximate Size
Kilobyte KB or K 1 thousand bytes
By number of bytes available for storage
Kilobyte KB or K 1 thousand bytes
Megabyte MB 1 million bytes
Gigabyte GB 1 billion bytes
Terabyte TB 1 trillion bytes
Actually a kilobyte = 1,024 bytes

28. Memory
What is random access memory (RAM)?
Also calledAlso called
Most RAM isMost RAM is
Memory chips that can beMemory chips that can be
read from and writtenread from and written
to by processor & other devicesto by processor & other devices
The more RAM aThe more RAM a
computer has, thecomputer has, the
faster it respondsfaster it responds
Also calledAlso called
main memorymain memory
or primaryor primary
storagestorage
volatilevolatile, it is lost, it is lost
when computer’swhen computer’s
power ispower is
turned offturned off

29. Memory
How do program instructions transfer in and out of RAM?
Step 1. When you start the computer,
certain operating system files are loaded
into RAM from the hard disk. The
operating system displays the user interface
on the screen.
Operating systemOperating system
instructionsinstructions
Web browserWeb browser
instructionsinstructions
Operating systemOperating system
interfaceinterface
Web browserWeb browser
windowwindow
RAM
Step 2. When you start a Web browser, the
program’s instructions are loaded into
RAM from the hard disk. The Web browser
window is displayed on the screen.
Word processingWord processing
program instructionsprogram instructions
Word processingWord processing
program windowprogram window
RAM
Web browser programWeb browser program
instructions areinstructions are
removed from RAMremoved from RAM
Web browserWeb browser
window is no longerwindow is no longer
displayed ondisplayed on
desktopdesktop
window is displayed on the screen.
Step 3. When you start a word processing
program, the program’s instructions are
loaded into RAM from the hard disk. The
word processing program, along with the
Web Browser and certain operating system
instructions are in RAM. The word
processing program window is displayed
on the screen.
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.

30. Do not have toDo not have to
be rebe re--energizedenergized
as often asas often as
DRAMDRAM
MostMost
commoncommon
typetype
Memory
What are two basic types of RAM chips?
StaticStatic
Must beMust be
rere--energizedenergized
constantlyconstantly
Faster andFaster and
more reliablemore reliable
than DRAMthan DRAM
chipschips
RAMRAM
(SRAM)(SRAM)
DynamicDynamic
RAMRAM
(DRAM)(DRAM)
Newer Type: Magnetoresistive RAM (MRAM)

31. 1 Gb SDRAM Dual-in-line Memory
Module

32. Two types of
DIMMs: a 168-pin
SDRAM module
(top) and a 184-pin
DDR SDRAM
module (bottom).
30- (top) and 72-pin
(bottom) SIMMs.
Early 30-pin
modules commonly
had either 256 KB or
1 MB of memory.
http://www.maplin.co.uk/images/Full/a23aj.jpg
http://www.makeitsimple.com/articles/ramguide/ramguidep2.htm

33. Memory
Where does memory reside?
Resides on small circuit
board called memory
module
Memory slots on
motherboard hold memory
dual inline memory module
motherboard hold memory
modules
memory chip memory slot

34. Memory
How much RAM does an application require?
Depends on the types of
software you plan to
use
For optimal
performance, youperformance, you
need more than
minimum specifications

35. Memory
How much RAM do you need?
Depends on type of applications you intend to run
on your computer
RAM
Use
256 MB to 1 GB 512 MB to 1 GB 2 GB and up
• Home and business
users managing
• Users requiring more advanced
multimedia capabilities
• Power users creating
professional Web sites
personal finance
• Using standard
application software
such as word processing
• Using educational
or entertainment
CD-ROMs
• Communicating with
others on the Web
• Running number-intensive
accounting, financial, or
spreadsheet programs
• Using voice recognition
• Working with videos, music, and
digital imaging
• Creating Web sites
• Participating in video conferences
• Playing Internet games
• Running sophisticated
CAD, 3D design, or
other graphics-intensive
software

36. Memory
What is cache?
L1 cache built into processor
L2 cache slower but has larger
Helps speed computer processes by storing frequently used
instructions and data
Also called memory cache
L2 cache slower but has larger
capacity
L2 advanced transfer cache is
faster, built directly on processor
chip
L3 cache is separate from processor
chip on motherboard (L3 is only
on computers that use L2 advanced
transfer cache)

37. Memory Cache
Cache speeds up processing time
It stores frequently used instruction & data.
When the processors needs them, it searches the
memory in an order with greater delay in
processing for each level of memory it must search
as the following order:as the following order:
L1 cache, then
L2 cache, then
L3 cache if it exists, then
RAM
If the instruction or data is not found in memory,
then it must search a slower speed storage medium
(h/disk, CD, or DVD)

38. Memory
What is read-only memory (ROM)?
Memory chips that storeMemory chips that store
permanent datapermanent data
and instructionsand instructions
Nonvolatile memoryNonvolatile memory, it is not, it is not
lost when computer’slost when computer’s
power is turned offpower is turned off
Three types:Three types:
EEPROMEEPROM
((eelectricallylectrically
eerasablerasable pprogrammablerogrammable
FirmwareFirmware——
ROM chips manufacturedROM chips manufactured
with permanently writtenwith permanently written
data, instructions,data, instructions,
or informationor information
eerasablerasable pprogrammablerogrammable
rreadead--oonlynly mmemory)emory)——
Type of PROMType of PROM
containing microcodecontaining microcode
programmerprogrammer
can erasecan erase
PROMPROM
((pprogrammablerogrammable
rreadead--oonlynly
mmemory)emory)——
Blank ROMBlank ROM
chip onto whichchip onto which
a programmera programmer
can write permanentlycan write permanentlyUse Microcode
instructions to program
a PROM chip
Erase microcode with an
electrical signal

39. Memory
What is flash memory?
Nonvolatile memory that can be erased electronically and rewritten
Used with PDAs, digital cameras, smart phones, music players, digital
voice recorders, printers, Internet receivers, and pagers
flash memoryflash memory
chips
USB
port
from the
computer
Portable media player
earphones
cable

40. Memory
What is CMOS?
Complementary
metal-oxide
semiconductor
memory
Used in some
RAM chips, flash
memory chips, and
other types of
memory chips
Uses battery
power to retain
information when
other power is
turned off
Stores date,
time, and
computer’s
startup
information
memory chips
The flash memory
chips that store
computer’s startup
information
often use CMOS
technology

41. Memory
What is access time?
Amount of time it takes processor
to read data from memory
Measured in nanoseconds (ns),
one billionth of a second
It takes 1/10 of a second to blink
10 million operations = 1 blink
It takes 1/10 of a second to blink
your eye; a computer can perform
up to 10 million operations in same amount of
time
Term Speed
Millisecond One-thousandth of a second
Microsecond One-millionth of a second
Nanosecond One-billionth of a second
Picosecond One-trillionth of a second

42. Memory Access Time
The access time (speed) of memory contributes to
the overall performance of the computer.
Accessing data in memory – 200,000 times faster
than h/disk, because of h/disk’s mechanical motion.
Access time also stated in MHz
667 MHz DDR2 SDRAM667 MHz DDR2 SDRAM
Divide 1 billion ns by the megahertz number
667 MHz = (1,000,000,000/667,000,000)ns ≈ 1.5ns
Manufacturers & retailers list a computer’s
memory in terms of its size, not its access time.
512 MB of SDRAM upgradeable to 4 GB

43. Expansion Slots and Adapter Cards
What is an adapter card?
A circuit board that
enhances system unit or
provides connections to
external devices called
peripherals – devicesperipherals – devices
connected to system unit &
controlled by processor:
modems, disk drives,
printers, scanners,
keyboards,…
Also called an
expansion card

44. Expansion Slots and Adapter Cards
What is an expansion slot?
An opening, or socket,
on the motherboard
that can hold an
adapter card
With Plug and Play,With Plug and Play,
the computer
automatically
configures cards
and other devices
as you install them

45. Expansion Slots and Adapter Cards

46. Expansion Slots and Adapter Cards
What are PC cards, and flash memory cards?
PC card
thin removable flash memory device to
enable wireless Internet access to
notebook computers
ExpressCard moduleExpressCard module
Next generation of PC Cards.
Removable flash memory device, to add
memory, storage, sound, fax/modem,
communications, and other capabilities
to computers

47. Expansion Slots and Adapter Cards
What are PC cards, and flash memory cards?
Flash memory card
allows users to transfer data from
mobile devices to desktop computers
storage capacity range: 32 MB – 8 GB
hot plugging – feature allows user tohot plugging – feature allows user to
insert & remove the removable flash
memory & other devices while
computer is running
USB Flash drive
flash memory storage that plugs in a
USB port on a computer
32 MB – 64 GB

48. Ports and Connectors
What are ports and connectors?
Port connects external devices to system unit
Connector joins cable to peripheral
Male connector: have 1 or more pins
Female connector: have matching hollows to accept the pins on a male
connector

49. Ports and Connectors
What are different types of connectors?

50. Ports and Connectors
What is a serial port?
Transmits one bit of data at a
time
Connects slow-speed devices,
such as mouse, keyboard,
modemmodem
E.g. COM port

51. Ports and Connectors
What is a parallel port?
Connects devices that can
transfer more than one bit at
a time, such as a printer
Can transfer 8 bits of data
(one byte) simultaneously(one byte) simultaneously
through 8 separate lines in a
single cable

52. Ports and Connectors
What are USB ports?
USB (universal serial bus) port can connect
up to 127 different peripherals together
with a single connector type
USB (universal serial bus) port can connect
up to 127 different peripherals together
with a single connector type
Third USB
device connects
to second USB
device, and so on
Third USB
device connects
to second USB
device, and so on
Second USB
device connects
to first USB
device
Second USB
device connects
to first USB
deviceFirst USB
device connects
to USB port
on computer
First USB
device connects
to USB port
on computer
Single USB port can
be used to attach
multiple peripherals
in a daisy chain
Single USB port can
be used to attach
multiple peripherals
in a daisy chain
PCs typically have
six to eight USB ports
on front or back of
the system unit
PCs typically have
six to eight USB ports
on front or back of
the system unit

53. Ports and Connectors
What are FireWire ports?
Similar to a USB port
Connects multiple types of devices that require
faster data transmission speeds: digital video
camera, color printer, scanners, digital cameras,camera, color printer, scanners, digital cameras,
DVD drives,…
Allows you to connect up to 63 devices together
Can use FireWire hub to attach multiple devices
to a single FireWire port

54. Ports and Connectors
What are special-purpose ports?
MIDI (Musical Instrument Digital Interface) port
eSata (external SATA – Serial Advances Technology
Attachment) port – connect SATA h/disk to computer
Not included in typical computer
Allow users to attach specialized peripherals or transmit data
to wireless devices
Attachment) port – connect SATA h/disk to computer
SCSI (small computer system interface) port
IrDA (Infrared Data Association) port – data transmission via
infrared light waves; need to align the IrDA port on the
device with IrDA port on the computer (like television
remote control)
Bluetooth port – Bluetooth technology uses radio waves to
transmit data between two devices; do not need to be
aligned with each other)

55. Ports and Connectors

56. Ports and Connectors
USB & FireWire ports are replacing
traditional ports completely

57. Buses
What is a bus?
Channel that allows devices
inside computer to communicate
with each other
Data bus – transfers actual data
Address bus – transfers the info. where
the data should reside in memorythe data should reside in memory
System bus connects processor and RAM
Bus width determines number of bits
transmitted at one time (32-bit, 64-bit bus)
Word size is the number of bits processor
can interpret and execute at a given time;
in most computers, the word size is the
same as the bus width
Bus clock speed: 1066 MHz
Memory
chips

58. Buses
System Bus/Front Side Bus (FSB)
Part of motherboard
Connects processor to main memory
Expansion Bus
Allows processor to communicate with peripherals
PCI bus (Peripheral Component Interconnect bus)PCI bus (Peripheral Component Interconnect bus)
PCI Express bus
Accelerated Graphics Port (AGP) bus
USB & FireWire bus
PC Card bus
FireWire
Bus
PCI
Bus
AGP
Bus
USB
Bus

59. Bays
What is a bay?
Open area inside system
unit used to install
additional equipment
Drive bays typically hold
disk drivesdisk drives
External drive bay – allow
user to access the drive from
outside the system unit: CD
& DVD drives
Internal drive bay – within
system unit: h/disk

60. Power Supply
What is a power supply?
Converts
AC Power
into
Fan keeps
system unit
components
External peripherals
might use an AC
adapter, which is an
external power supply
DC Power cool
One end of AC adapter plugs in the wall outlet
& the other end attached to the peripheral.
The AC adapter converts the AC power into DC
power that the peripheral requires.

61. Mobile Computers and Devices
What is a mobile computer?
Notebook, weighing between 2.5 and 8 pounds, or
mobile device such as a PDA

62. Mobile Computers and Devices
What ports are on a notebook computer?

63. Mobile Computers and Devices
What ports and slots are on a tablet PC?

64. Putting It All Together
What are suggested processor, clock speed, and RAM
requirements based on the needs of various types of
users?

65. Keeping Your Computer Clean
Over time, the system unit collects dust – even in a
clean environment
Preventative maintenance requires a few basic
products: