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Lecture # 3

11/16/2012 Designed by Prof. Anosha Khan PGC 1

 It contains system unit

electronic
components of
the computers
used to process
data system unit

system unit

system unit


power supply drive bays
 Processor
 Memory processor

 Adapter cards
 Sound card memory
ports
 Modem card
 Ports
 Drive bays
 Power supply sound card

video card
modem card
network card


 Circuit board:
thin board containing chips—very small pieces of silicon
or other semi-conducting material onto which integrated
circuits are embedded—and other electronic components
 Mother Board
 Main circuit board in system unit
 Contains adapter cards, processor chips, and
memory chips
 Connects all components
 Allows communication between devices
 Also called system board

adapter cards
processor chip

memory chips

memory slots

Expansion
slots for
adapter cards motherboard


 Small piece of semi-
conducting material on
which integrated circuits
are etched
 Integrated circuits contain
many microscopic
pathways capable of
carrying electrical current


Processor
 Interprets and carries Control
Control Arithmetic
Arithmetic
out basic instructions Unit
Unit Logic Unit (ALU)
Logic Unit (ALU)

that operate a computer Information
Data
 Also called the Information

processor
Input Output
Devices
Data Memory Information
Devices

Information
Data
Information

Storage
Devices

 Arithmetic/Logic Unit (ALU)
 Perform two types of operations
 Arithmetic (+,-,*,/) and logic(<,>,=)
 Control Unit
 Tell the rest of the computer how to carry out a program’s
instructions
 Works with a “program counter” (address of next instruction)
 It directs the movement of electronic signals between memory,
instructions and arithmetic logic unit.
 Direct control signals between the CPU and I/O devices.


 There are four operations of Machine Cycle
Step 1. Fetch
Obtain program instruction or data item from
memory
Step 2. Decode
Translate instruction into commands
Step 3. Execute
Carry out command
Step 4. Store
Write result to memory

 CPU begins fetching second instruction before
completing machine cycle for first instruction
 Results in faster processing


 Important measurement indicating speed
 Located on a small chip
 Produces electrical beats(impulse)
 Expressed in gigahertz (1 GH=1 billion ticks
of system clock per second)
 Faster clock speed, faster computer
 the clock speed determines how many
instructions per second the processor can
execute
 Processor speed can also be measured in
millions of instructions per second (MIPS)

 Registers
 Page # 145, topic: Registers
 Cache
 System Clock
 RAM


heat sink fan
 Heat sink—component
with fins that cools
processor

 Heat pipe—smaller
device for notebook
computer


Control Processor
 Using multiple
processors
simultaneously to
Processor 1 Processor 2 Processor 3 Processor 4
execute a program Memory Memory Memory Memory
faster
 Requires special
software to divide
problem and bring
Results combined
results together


 Most Computers are digital
 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)


 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


 Three types of schemes
 ASCII - American Standard Code for Information
interchange
 EBCDIC - Extended Binary Coded Decimal
Interchange Code( used for large computers)
 Unicode ( for international languages like Chinese
and Japanese. ASCII Symbol EBCDIC
00110000 0 11110000
00110001 1 11110001
00110010 2 11110010
00110011 3 11110011

 How is a letter converted to binary form and back?
Step 1. Step 2.
The user presses An electronic signal for the
the capital letter D capital letter D is sent to the
(shift+D key) on system unit.
the keyboard.

Step 4. Step 3.
After processing, the binary The signal for the capital letter D
code for the capital letter D is is converted to its ASCII binary
converted to an image, and code (01000100) and is stored in
displayed on the output device. memory for processing.


 Electronic components that store instructions, data, and results
 Consists of one or more chips on motherboard or
other circuit board
 Before running a Program must be loaded into the memory
 Memory slots on motherboard hold memory modules
 RAM (random access memory): temporary memory that the
computer uses
 Consists of chips connected to a memory module which is
connected to the motherboard
 Hold data and program instructions while they are needed.
 RAM is volatile, its content is lost
when the computer is shut off


Memory chips that can be
 Home Task read from and written
Explore to by processor
SRAM, DRAM,
Most RAM is
SIMM, DIMM and Also called
main memory
volatile, it is lost
when computer’s
RIMM or primary
storage
power is
turned off
 Virtual Memory
Small portion of The more RAM a
hard Disk acts as computer has, the
faster it responds
RAM

 Types of Memory
Volatile , non volatile
 How is memory measured?
By number of bytes available for storage
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


RAM

Operating system Operating system
instructions interface

Step 1. When you start the computer, certain operating system
files load into RAM from the hard disk. The operating system
displays the user interface on the screen.
Word processing Word processing
program instructions program window

Step 2. When you start a word processing program, the
program’s instructions load 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.

 It helps to increase speed of computer
 It stores frequently used data and instructions
 Two types of cache
Memory Cache and Disk Cache
 Memory Cache
 L1: built directly in processor, less memory
 L2:slower but has larger capacity
ATC (advanced transfer cache) is a type of
L2 cache
 L3:it is on motherboard separate from
processor


 A register is a single storage location within the CPU
 Unlike memory, which is “outside” the CPU
 Examples of registers:
 Accumulator (ACC)
 Program counter (PC)
 Instruction register (IR)
 Memory address register (MAR)
 Memory data register (MDR)
 Status register
 General purpose registers (R0, R1, …)
 Included on some CPUs
 Used for high-speed temporary storage of program
variables

 Memory chips that store
permanent data
and instructions
 Nonvolatile memory, it is not
lost when computer’s
power is turned off
 PROM (programmable ROM)
 EEPROM (Electrically erasable read-only memory)


 Nonvolatile memory that can be erased
electronically and reprogrammed
 Used with PDAs, digital cameras, digital
cellular phones, music players, digital voice
recorders, and pagers


 CMOS stands for Complementary metal-oxide
semiconductor memory
 It is used to store configuration information
about the computer
 Uses battery
power to retain information when other power
is turned off
 Stores date, time, and computer’s startup
information

 What is an adapter card?
 Enhances system unit or provides connections to
external devices called peripherals
 Also called an expansion card
 Flash Memory Cards
 PC Cards


 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

 Port connects
external devices to
system unit
 Connector joins
cable to peripheral
 Available in one
of two genders:
male and female


 Transmits one bit of data
at a time
 Connects slow-speed
devices, such as mouse,
keyboard, modem


 Connects devices that
can transfer more than
one bit at a time, such as
a printer


 Connect parts of the CPU to each other
 Connect the CPU to other devices on the system board.
 Data roadway for traveling bits
 Measured as bus width( number of bits transmitted at one time)
 More lanes, faster traffic
 Two basic categories of Expansion BUSES
 System buses ( connect CPU to Memory)
 Expansion buses ( connect CPU to slots on the system board)
 Data Bus (Page # 148)
 Address Bus__Connects only CPU & RAM(Page # 148)
 BUS standard (chapter 4 page 148)


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System unit & its components

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