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Components
of
System Unit
Course Instructor: Fariha Sabahat
1

The System Unit
• What is the system
unit?
 Case that contains electronic
components of the computer used
to process data
 Sometimes called
the chassis
2

The System Unit
• What are common components inside the
system unit?
 Memory
 Adapter cards
 Sound card
 Modem card
 Video card
 Network card
 Ports
 Drive bays
 Power supply
power supply
ports
drive bays
processor
memory
sound card
video card
modem card
network card
 Processor
3

The System Unit
• What is the
motherboard?
 Main circuit
board in system
unit
 Contains adapter
cards, processor
chips, and
memory chips
 Also called
system board
processor chip
adapter cards
memory chips
memory slots
motherboard
Expansion
slots for
adapter cards
5

The Motherboard and CPU
• The motherboard is the main
circuit board of a
microcomputer. It contains
the central processing unit
(CPU), the Basic Input/Output
System (BIOS), memory,
mass storage interfaces,
serial and parallel ports,
expansion slots, and all the
controllers for standard
peripheral devices like the
keyboard, disk drive and
display screen.
6

The System Unit
• What is a chip?
dual inline
packages (DIP)
holds memory
chips
pin grid
array (PGA)
package
holds processor
chips
 Small piece of semi-conducting
material on which integrated
circuits are etched
 Integrated circuits contain
many microscopic pathways
capable of carrying electrical
current
 Chips are packaged so they can
be attached to a circuit board
7

Processor
Control
Unit
Arithmetic
Logic Unit (ALU)
Arithmetic
Logic Unit (ALU)
Processor
What is the central processing unit (CPU)?
Input
Devices
Storage
Devices
Output
Devices
 Interprets and carries
out basic instructions
that operate a computer
Memory
Data Information
Instructions
Data
Information
Instructions
Data
Information
Control
Unit
 Control unit directs and
coordinates operations in
computer
 Arithmetic logic unit
(ALU) performs
arithmetic, comparison,
and logical operations
 Also called the processor
8

Processing Sequence
Two crucial aspects are related with Processors
& Processing
1. Machine Cycles
• Control unit and memory working together to perform all
instructions on computer
• Two cycles
– Instruction Cycle (Fetch instruction and translate them)
– Fetch
– Decode
– Execution Cycle (Process and Produce(store) results)
– Execute
– Store
9

Processing Sequence
2. Registers
• To execute machine cycles, the control unit needs temporary
storage spaces called “Registers”
• Part of Processor not Storage or Memory devices
• These are faster than the main memory
• Their purpose is to hold most frequent instructions carried out
by processors and therefore they eventually speeds us the
execution process
10

Stores location
from where instruction
was fetched
Processor
Stores
instruction while it is
being decoded
• What is a register?
Stores data
while ALU
computes it
Stores results
of calculation
 Temporary high-speed storage area that holds
data and instructions
11

Processor
Control Unit
Memory
ALU
Processor
What is a machine cycle?
Step 1. Fetch
Obtain program instruction
or data item from memory
Step 2.
Decode
Translate
instruction into
commands
Step 4. Store
Write result to memory
Step 3. Execute
Carry out command
 Four operations of the CPU comprise a machine cycle
13

Processor
• What is pipelining?
 CPU begins fetching second instruction before
completing machine cycle for first instruction
 Results in faster processing
15

Processor
What is the system clock?
FLOPS
Floating Point Operations
per second
Pace of system
clock is clock speed
Most clock speeds are
in the gigahertz (GHz)
range (1 GHz = one
billion ticks of system
clock per second)
Processor speed can
also be measured in
millions of instructions
per second (MIPS)
 Controls timing of all computer operations
 Generates regular electronic pulses, or ticks, that set
operating pace of components of system unit
 Each tick is a clock cycle (million to billion times in 1 sec)
16

Chip-for chip upgrade
replace the chip
Processor
• What are the types of processor
upgrades?
Piggyback upgrade
stack new chip on top of old one
Daughterboard upgrade
chip is on adapter card that plugs into motherboard
17

Processor
What is a zero-insertion force (ZIF) socket?
Step 2.
Insert the chip.
Step 1.
Lift the lever on the socket.
lever
Step 3.
Push the lever down.
lever
 Allows you to install and remove chips with no force
18

Processor
What is parallel
processing?
Control Processor
Processor 1
Memory
Processor 2
Memory
Processor 3
Memory
Processor 4
Memory
Results combined
 Using multiple
processors
simultaneously to
execute a program
faster
 Requires special
software to divide
problem and bring
results together
 SIMD v/s MIMD
19

Data Representation
How do computers represent data?
 Recognize only two
discrete states: on or off
 Use a binary system to
recognize two states
 Use Number system with
two unique digits: 0 and
1, called bits (short for
binary digits)
 Most computers are digital
20

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
 Uppercase
and lowercase
letters
 Punctuation
marks
 Encoding
21

Data Representation
What are three popular coding systems to represent
data?
 ASCII—American Standard Code for Information Interchange
 EBCDIC—Extended Binary Coded Decimal Interchange Code
 Unicode—coding scheme capable of representing all
world’s languages
ASCII Symbol EBCDIC
00110000 0 11110000
00110001 1 11110001
00110010 2 11110010
00110011 3 11110011
22

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.
23

Memory
What is memory?
 Electronic components that
store instructions, data, and
results
 Consists of one or
more chips on
motherboard or
other circuit board
 Each byte stored
in unique location
called an address,
similar to seats
on a passenger train
Seat #2B4 Seat #2B3
24

Memory
How is memory measured?
Term Abbreviation Approximate Size
Kilobyte KB or K 1 thousand bytes
Megabyte MB 1 million bytes
Gigabyte GB 1 billion bytes
Terabyte TB 1 trillion bytes
 By number of bytes available for storage
25

Memory
What is random access memory (RAM)?
The more RAM a
computer has, the
faster it responds
Also called
main memory
or primary
storage
Most RAM is
volatile, it is lost
when computer’s
power is
turned off
Memory chips that can be
read from and written
to by processor
26

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 system
instructions
Web browser
instructions
Word processing
program instructions
Operating system
interface
Web browser
window
Word processing
program window
RAM
RAM
Web browser program
instructions are
removed from RAM
Web browser
window no longer is
displayed on
desktop
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.
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 no longer
is displayed on the screen.
27

Faster
variations
of DRAM are
SDRAM and
RDRAM
Used for
special
applications
such as
cache
Most
common
type
Faster and
more reliable
than DRAM
chips
Memory
What are two basic types of RAM chips?
Dynamic
RAM
(DRAM)
• Future: Magnetoresistive RAM (MRAM)
Static
RAM
(SRAM)
28

Memory
• Where does memory
reside?
 Resides on small circuit
board called memory
module
 Memory slots on
motherboard hold memory
modules
memory chip memory slot
dual inline memory module
29

Memory
How much RAM does an application require?
 Software package
typically indicates
RAM requirements
 For optimal
performance, you
need more than
minimum specifications
System Requirements
Windows® XP Home Edition/Professional
• Intel Pentium processor at 233MHZ or higher
• AMD K6 (Athlon Duron Family processor at 233MHZ or higher
• 64 MB of RAM
30

Memory
How much RAM do you need?
 Depends on type of applications you intend to run
on your computer
RAM
Use
128 to 256 MB 256 to 1 GB 1 GB and up
• Home and business
users managing
personal finance
• Using standard
application software
such as word processing
• Using educational
or entertainment
CD-ROMs
• Communicating with
others on the Web
• Users requiring more advanced
multimedia capabilities
• 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
• Power users creating
professional Web sites
• Running sophisticated
CAD, 3D design, or
other graphics-intensive
software
31

Memory
What is cache?
 L1 cache built into processor
 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)
 256 KB of L2 for Personal computers
 2 MB of L2 for Servers
 Helps speed computer processes by storing frequently used
instructions and data
 Also called memory cache
32

Memory
What is read-only memory (ROM)?
Memory chips that store
permanent data
and instructions
Nonvolatile memory, it is not
lost when computer’s
power is turned off
Three types:
Firmware
Manufactured with
permanently written
data, instructions,
or information
EEPROM
(electrically
erasable programmable
read-only memory)—
Type of PROM
containing microcode
programmer
can erase
PROM
(programmable
read-only
memory)—
Blank ROM
chip onto which
a programmer
can write permanently 33

Memory
What is flash memory?
Step 1.
Purchase and download MP3 music tracks
from a Web site. With one end of a special
cable connected to the system unit, connect
the other end into the MP3 player.
Step 2.
Instruct the computer to copy the MP3 music track
to the flash memory chip in the MP3 player.
Step 3.
Plug the headphones into the MP3
player, push a button on the MP3
player, and listen to the music
through the headphones.
MP3 Player
Flash memory chip
Flash memory card
From computer
To headphones
 Nonvolatile memory that can be erased electronically and
reprogrammed
 Used with PDAs, digital cameras, digital cellular phones, music players,
digital voice recorders, printers, Internet receivers, and pagers
34

Memory
What is CMOS?
Uses battery
power to retain
information when
other power is
turned off
Stores date,
time, and
computer’s
startup
information
Complementary
metal-oxide
semiconductor
memory
Used in some
RAM chips, flash
memory chips, and
other types of
memory chips
35

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
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
36

Expansion Slots and Adapter Cards
What is an adapter card?
Types of Adapter Cards
 Enhances system unit or
provides connections to
external devices called
peripherals
 Also called an expansion card
37

What is an expansion slot?
 An opening, or socket,
on the motherboard
that can hold an
adapter card
 With Plug and Play,
the computer
automatically
configures cards
and other devices
as you install them
39

PCMCIA (PC Card)
• Personal Computer Memory Card
International Association
• Found on notebook computers
40

What are PC cards and flash memory cards?
 A PC card adds memory, storage,
sound, fax/modem,
communications, and other
capabilities to notebook computers
 A flash memory card allows users
to transfer data from mobile
devices to desktop computers
 Hot plugging allows you to insert
and remove cards while computer
is running 41

Ports and Connectors
What are ports and connectors?
 Port connects external devices to system unit
 Connector joins cable to peripheral
 Available in one of two genders: male and female
42

What are different types of connectors?
43

What is a serial port?
 Transmits one bit of data at a
time
 Connects slow-speed devices,
such as mouse, keyboard,
modem
44

What is a parallel port?
 Connects devices that can
transfer more than one bit at
a time, such as a printer
46

Third USB
device connects
to second USB
device, and so on
Second USB
device connects
to first USB
device
First USB
device connects
to USB port
on computer
Single USB port can
be used to attach
multiple peripherals
in a daisy chain
PCs typically have
four to eight USB ports
on front or back of
the system unit
What are USB ports?
USB (universal serial bus) port can connect
up to 127 different peripherals together
with a single connector type
47

What are special-purpose ports?
 FireWire port
 MIDI (Musical
Instrument Digital
Interface) port
 SCSI (small
computer system
interface) port
 IrDA (Infrared Data
Association) port
 Bluetooth port
 Allow users to attach specialized peripherals (digital video
cameras, color printers, scanners, and disk drives) or
transmit data to wireless devices
48

Buses
What is a bus?
 Channel that allows devices
inside computer to
communicate with each other
 System bus connects processor
and RAM
 Bus width determines number
of bits transmitted at one time
 Word size is the number of
bits processor can interpret
and execute at a given time
49

Buses
What is an expansion bus?
 Allows processor to communicate with peripherals
50

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