Discovering Computers
Chapter 4
The Components of the System
Unit
Ch 1 –
Introduction
Ch 2 –
Internet &
WWW
Ch 3 –
Application
Software
Ch 4
System Unit
Arithmetic
Control
Logic
Unit
Unit
(ALU)
Ports
Cards
Buses
Clock
Power
Drives
Instruction
Data
Information
Input
Devices
Ch 5
Memory
Information
Data
Instructions
Data
Information
Storage
Devices
Ch 7
Output
Devices
Ch 6
2
What is the system unit?
 Case that contains
electronic components
of the computer used
to process data
3
What is the motherboard?


Main circuit
board of the
system unit
Also called
system board
4
Components inside the system unit?




Processor
Memory
Clock
Adapter
(extension)
cards






Sound card
Video card
Drive bays
Power supply
Ports
Buses
5
Processor
The processor, also called the central
processing unit (CPU), interprets and
carries out the basic instructions that
operate a computer
Contains a control unit and an arithmetic
logic unit (ALU)
6
Control unit is the component of the
processor that directs and coordinates
most of the operations in the computer
Arithmetic logic unit (ALU)
performs arithmetic, comparison, and
other operations
7
For every instruction, a processor
repeats a set of four basic operations,
which comprise a machine cycle
8
Step 1. Fetch
Obtain program
instruction from
memory
Step 4. Store
Write result to
memory
Memory
Processor
Control Unit
ALU
Step 3. Execute
Carry out
command
Step 2.
Decode
Translate
instruction
into
commands
9
The processor contains
registers, that hold data and
instructions
The processor contains
circuits that perform
instructions using data
10
The system clock
controls the timing of
all computer operations
11
System Clock
Generates regular electronic pulses, or ticks, that set
operating pace of components of system unit
How speed of the processor is measured?
Each tick
is a
clock cycle
Pace of system
clock is clock speed
Clock speeds are
in the gigahertz (GHzbillion ticks per sec)
Processor speed
is also measured in
millions of instructions
per second (MIPS)
13
 Clock speed (GHz)
 Instructions per sec (MIPS)
Instructions per 1 watt energy
(in millions)
(MIPW)
14
What is pipelining?

CPU begins executing the second instruction
before completing the first instruction
Machine Cycle (without pipelining)
Machine Cycle (with pipelining)
Instruction 1
Instruction 2
Instruction 3
Instruction 4
15
Doing Laundry
Ann, Brian, Cathy, Dave each have one
load of clothes to wash, dry, fold, slash
A B C D
° Washer takes 30 minutes
° Dryer takes 30 minutes
° Folder takes 30 minutes
° Stasher takes 30 minutes
16
Sequential Laundry
6 PM 7
T
a
s
k
O
r
d
e
r
A
8
9
10
11
12
1
2 AM
30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30
Time
B
C
D
Sequential laundry takes 8 hours for 4 loads
17
Pipelined Laundry
6 PM 7
T
a
s
k
8
9
3030 30 30 30 30 30
10
11
12
1
2 AM
Time
A
B
C
O
D
r
d
e
r
Pipelined laundry takes 3.5 hours for 4 loads
18
What is parallel processing?


Using multiple
processors
simultaneously
to execute a
program faster
Requires special
software to
divide problem
and bring results
together
Control Processor
Processor 1
Processor 2
Processor 3
Processor 4
Memory
Memory
Memory
Memory
Results combined
19
Single-core
processor
One processor
on a chip
Multi-core
processor
More then one
processor on a chip
20
Data of various nature
are presented inside a
computer in a digital
form. We will see how.
21
Analog signals are continuous
and vary in strength and quality
Digital signals are in one of two
states: on or off
22
What is a bit?
23
Eight bits grouped together as a unit are
called a byte.
Each byte has a unique address.
Each of eight bits in a byte has a position
24
What a byte contains vs. what an
output device will convey?
Contains: A sequence of 8 binary digits
Means:
 Number






Character
Instruction
Sound pitch
Color
…
Depending on device
25
Representing numbers


Numbers have the most natural
presentation. Each bit of a byte has a
value depending on the position of the bit
in a byte.
For example byte 01010101 carries
numeric value of 64+16+4+1 = 85
26
Coding systems to represent
text data

ASCII—American Standard Code for Information
Interchange

Unicode—coding scheme capable of representing all
world’s languages
27
28
Memory
29
Memory consists of electronic components that store
instructions waiting to be executed by the processor,
data needed by those instructions, and the results of
processing the data
What has to be stored?
The operating
system and other
system software
Application
programs
Data being
processed and the
resulting
information
30
31
Memory consists of locations (bytes). Each location in
memory has an address
The number of locations in memory is memory size.
It is measured in kilobytes (KB or K), megabytes (MB),
gigabytes (GB), or terabytes (TB)
32
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: RAM
Examples: ROM,
flash memory
33
Read-only memory (ROM)
refers to memory chips storing
permanent data and
instructions
34
Adapter (Extension) Cards


A flash memory card allows
users to transfer data from
mobile devices to desktop
computers
An PC card adds various
capabilities to computers
35
Flash memory can be electronically rewritten
36
Flash memory includes:
 Memory cards, USB flash drives, and PC Cards modules
37
Memory cache speeds the processes of the
computer because it is faster than memory
and stores repeatedly used information
38
Access time is the amount
of time it takes the
processor to read from
memory. Measured in
nanoseconds
39
Expansion slot
holds an
adapter card
Adapter card
enhances
functions and
provides
connections to
peripherals
40
With Plug and Play, the computer automatically
configures adapter cards and peripherals as you
install them
41
Ports and Connectors
A port is the point at which a
peripheral attaches to or
communicates with a system unit
(sometimes referred to as a jack)
A connector joins a cable to a port
42
 Port connects external devices to system unit
43
On a notebook computer, the ports are on the back,
front, and/or sides
44
45
What are USB ports?
USB (universal serial bus) port can connect
up to 127 different peripherals together
with a single connector type
PCs typically have
several USB ports
USB 2.0
Single USB port can
be used to attach
multiple peripherals
First USB
device connects
to USB port
Third USB
device connects
to second USB,
and so on
Second USB
device connects
to first USB
46
You can attach multiple peripherals using a single
USB port with a USB hub
47
Other types of ports include:
Firewire
port
Bluetooth
port
SCSI
port
eSATA
port
IrDA
port
Serial
port
MIDI
port
48
What are special-purpose ports?
 Allow users to attach specialized peripherals or
transmit data to wireless devices
 MIDI (Musical Instrument Digital Interface) port
 IrDA (Infrared Data Association) port
 Bluetooth port
49
50
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
51
What is a serial port?


Transmits one bit of data at a
time
Connects slow-speed devices,
such as mouse, keyboard,
modem
52
What is a parallel port?

Connects devices
that can transfer
more than one bit
at a time, such as a
printer
53
Buses
What is a bus?
 Channel that allows devices
inside computer to
communicate with each other
 Bus width determines
number of bits transmitted
at one time
54
Bays
What is a bay?


Opening inside system
unit used to install
additional equipment
Drive bays typically
hold disk drives
55
Power Supply and cooling
Converts
AC Power
into
DC Power
Fan keeps
system unit
components cool
56
To see the online addition
to the book click here