Transcript Chapter 4

Chapter 4
The Components of the
System Unit
The System Unit
Case that contains electronic components of the computer
used to process data
The System Unit
Common components inside the system unit
Processor
Memory
Adapter cards
Ports
Drive bays
Power supply
Motherboard
Main circuit board in system unit
Contains;
CPU
Other IC’s
Expansion slots
Expansion cards
Memory slots
Memory modules
Ports
Motherboard
The Integrated Circuit (Chip)
Small piece of semi-conducting material on which integrated
circuits are etched
Motherboard
The Integrated Circuit (Chip)
Integrated circuits contain many microscopic pathways
capable of carrying electrical current
Data Representation
The basic building block of the CPU is the transistor. A CPU
can contain millions of them.
Transistors can be only two electric charge states, + or -.
This creates the binary numbering system recognize two
electronic states On and Off.
The binary
numbering system
uses two unique
digits: 0 and 1,
called bits (short for
binary digits)
Data Representation
A bit by itself is not sufficient to produce useable information.
Computers use bytes
A byte is made up of eight bits, this provides 256 different
combinations of 1’s and 0’s to create usable information.
8-bit byte for the number 3
8-bit byte for the number 5
8-bit byte for the capital letter T
Data Representation
There are three popular
coding schemes for bytes
used in computing
ASCII - American
Standard Code for
Information Interchange
EBCDIC - Extended
Binary Coded Decimal
Interchange Code
Unicode - coding scheme
capable of representing
all world’s languages
Data Representation
Converting to and from binary
Step 1.
The user presses the capital letter D
(shift+D key) on the keyboard.
Step 4.
After processing, the binary code for the
capital letter D is converted to an image,
and displayed on the output device.
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.
Central Processing Unit (CPU)
How components interact
Control Unit
CPU
Arithmetic Logic Unit
Instructions
Data
Information
Input
Devices
Data
Memory
Information
Instructions
Data
Information
Storage Devices
Output
Devices
Central Processing Unit (CPU)
The two major components of the CPU are;
CPU
Control Unit
Arithmetic/
Logic Unit
(ALU)
Central Processing Unit (CPU)
The control unit interprets and carries out basic instructions
that operate a computer
The control unit repeats four basic
operations
Fetch - obtain program
instruction or data item from
memory
Decode - translate instruction
into commands
Execute - carry out command
Store - write result to memory
Control Unit
Central Processing Unit (CPU)
The four operations of the CPU comprise a machine cycle.
Instruction time (i-time) - time taken to fetch and decode
Execution time (e-time) - time taken to execute and store
CPU speed is measured in MIPS (millions of instructions per
second)
e-time
i-time
Central Processing Unit (CPU)
The ALU (arithmetic/logic unit) executes mathematical and
logical operations requested by programs.
Comparison
(greater than,
equal to, or less
than)
Arithmetic
(addition, subtraction,
multiplication, and
division)
Logical
(AND, OR,
NOT)
Central Processing Unit (CPU)
System Clock
The system clock is a small chip on the mother board that
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
Central Processing Unit (CPU)
System Clock
There are two ways to measure the speed of a computer
clock speed
MIPS
Pace of system
clock is clock speed
Processor speed can
also be measured in
millions of instructions
per second (MIPS)
Most clock speeds are
in the gigahertz (GHz)
range (1 GHz = one
billion ticks of system
clock per second)
Central Processing Unit (CPU)
Cooling Systems
A great deal of heat is generated in the CPU and other
components of the system unit
Types of cooling devices:
Heat sink—component
with fins that cools
processor
Heat pipe—smaller
device for notebook
computers
Fans
Memory
Electronic components that store instructions, data, and
information.
Consists of one or more chips or memory modules on
motherboard
Each byte stored in unique location called an address,
similar to seats on a passenger train
Memory is measured by the number of byte of storage
available
Memory
Term
Abbreviation Approximate
memory size
Exact memory
amount
Number of
Pages of
Text
Kilobyte
Kb or K
1 thousand bytes 1024 bytes
½
Megabyte
MB
1 million bytes
1.048,576
500
Gigabytes
GB
1 billion bytes
1,073,741,824
500,00
Terabytes
TB
1 trillion bytes
1,099,511,627,776
500,000,000
Memory
512.000.000 bytes of memory (512 meg)
X
8 bits in a byte
=
4,096,000,000 transistors
Memory
There are two types of memory found on in the system unit.
volatile memory
Loses its contents
when computer's
power
is turned off
nonvolatile
memory
Does NOT lose its
contents when
computer’s power
is turned off
Memory
RAM Random Access Memory
Memory chips that can be read from and written to by
processor
Also called main memory or primary storage
Most RAM is volatile, it is lost when computer’s power is
turned off
The more RAM a computer has, the faster it responds
Memory
How Programs are transferred in and out of RAM
RAM
Operating system
instructions
Operating system
interface
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.
Memory
How Programs are transferred in and out of RAM
RAM
Web browser
instructions
Web browser
window
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.
Memory
How Programs are transferred in and out of RAM
RAM
Word processing
program
instructions
Word processing
program window
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.
Memory
How Programs are transferred in and out of RAM
RAM
Word processing
program
instructions
Word processing
program window
Web browser
program
instructions are
removed from
RAM
Web browser
window no longer
is displayed on
desktop
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.
Memory
The two basic types of RAM chips
Static
RAM
(SRAM)
Most
common
type
Faster
variations
of DRAM are
SDRAM and
RDRAM
Dynamic
RAM
(DRAM)
Used for
special
applications
such as
cache
Faster and
more reliable
than DRAM
chips
Memory
Memory Modules
RAM memory is found on
memory modules.
Memory slots on motherboard
hold memory modules
Memory modules come is
specific sizes and speeds.
Memory
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
BIOS (basic input/output system)
Stored on ROM
Sequence of instructions computer follows to load operating
system and other files when you turn on the computer
Memory
Flash memory
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
Memory
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
under Widows XP operating
system
Expansion Slots and Adapter Cards
Plug and Play
The computer automatically configures cards and other
devices as you install them
Memory
Memory Access Time
Amount of time it takes processor to read data from memory
Measured in nanoseconds (ns), one billionth of a second
When adding memory to a PC you must make sure that it
has the same access time
Term
Speed
Millisecond
Microsecond
Nanosecond
Picosecond
One-thousandth of a second
One-millionth of a second
One-billionth of a second
One-trillionth of a second
Expansion Slots and Adapter Cards
Expansion slot is an opening, or socket, where circuit board
is inserted into motherboard
Expansion card inserted in expansion slot
Expansion cards are used to improve the quality of the
existing components on the mother board including
Video Cards
Audio Cards
Port Cards
Expansion cards are being replaced by components on the
mother board and USB
Expansion Slots and Adapter Cards
PC cards
A PC card adds memory, storage, sound, fax/modem,
communications, and other capabilities to notebook
computers
Ports and Connectors
Types of Ports
USB port
USB (universal serial bus) port can connect up to 127
different peripherals together with a single connector type
PCs typically have four to eight USB ports on front or back of
the system unit
To attach multiple devices to one USB port you use a USB
hub
Ports and Connectors
Types of Ports
Firewire port
Can connect different peripherals together with a single
connector type
High speed transfer of data
First developed by Apple.
Used mostly for video transfer.
Ports and Connectors
Types of Connectors
Bays
Open area inside system
unit used to install
additional equipment
Power Supply
Converts AC Power into DC Power
Fan keeps system unit components cool
External peripherals might use an AC adapter, which is an
external power supply
Mobile Computers and Devices
Include notebook, weighing between 2.5 and 8 pounds,
or mobile device such as a PDA
Mobile Computers and Devices
The system unit of a
mobile computer
Motherboard,
processor, and
memory—also
devices such as the
keyboard,
speakers, and
display
Mobile Computers and Devices
Ports on a Notebook computer
Docking bay for notebook computers