Transcript The System Unit

The System Unit
• How a computer uses binary codes to
represent data
• Major system unit components
• 3 types of memory
• 4 principal types of bus lines
• 4 types of ports
From Page 10~Page 15 on Textbook
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The System Unit
• Judge how fast, powerful and versatile a
particular microcomputer is
– Speed, capacity, flexibility
– For buy or upgrade
– Evaluate whether the existing system is
powerful enough
• The basic components
– System board, microprocessor, memory,
system clock
– Expansion slots and cards, bus lines, ports,
cables
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System Unit
• System cabinet，or chasis
– Houses most of the electronic components
• 3 basic types of microcomputers
– Desktop system units
• Inside: system’s electronic components,
secondary storage devices
• Outside: input and output devices
– Notebook system units
• Inside: system’s electronic components,
secondary storage devices, input devices
• Outside: monitor
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– PDA system units
• All inside
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Electronic data and instructions
• Represented electronically with a binary,
or two-state, numbering system
– Two-state is more easy to realize
• Binary system
– Consists of only two digits: 0 and 1
– Bit: each 0 or 1
– Byte: combined into group of 8 bit
• Typically represents one character
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Binary coding schemes
• How are characters represented as 0s and 1s in the
computer?
• ASCII
– American Standard Code for Information Interchange
– Uses 8 bits to form each byte
– Most widely used binary code for microcomputers
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Binary coding schemes
• EBCDIC
– Extended Binary Coded Decimal
Interchange Code
– Use 8 bits to form each byte
– Developed by IBM
– Used primarily for large computers
• Unicode
– Designed to support international languages
– 16-bit code
– Support from Apple, IBM and Microsoft
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Binary coding schemes
• Coding schemes are very important
– Files shared by different computers or
applications
– Use same coding scheme: no problem
– Use different coding scheme
• Must be translated
• Using special conversion programs
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Example of coding
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System Board
• Also called main board/motherboard
• Every component of the system unit
connects directly to the system board
• External devices could not communicate
with the system unit without system
board
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System Board
• In desktop computer
– Located at the bottom of the system
unit
– Large flat circuit board covered with
sockets and a variety of chips
• Chip:
– silicon with tiny circuit board on it
– Also called silicon chip, semiconductor,
integrated circuit
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Microprocessor
• CPU: central processing unit / processor
– In a single chip in microcomputer
– Brain of the system
– 3 components
• Control unit
– How to carry out a program’s instructions
– How electronic signals move
• Arithmetic-logic unit(ALU)
– Arithmetic operations
» Addition, subtraction, multiplication, division
– Logical operations
» Two pieces of data are compared
» Equal to, less than, greater than
• Registers
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2 Sides of a CPU
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The principal subsystem of a
computer
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A. Control Unit
Control Unit
Directs and co-ordinates most of the operations in the
computer.
Interprets each instruction and then initiates the action.
Machine Cycle
a. Fetch the instruction
b. Decode
c. Fetch the data
d. Execute
f. Store the results
MIPS (MILLION INSTRUCTIONS PER SECOND) IS
ANOTHER MEASUREMENT OF CPU SPEED.
IT Fundamentals
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Instruction Interpretation
• Example:ADD 800, 428,884
• PC(program counter): 2200
• Computer before an ADD instruction
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Instruction Fetch
• Move instruction from memory to the
control unit
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Instruction Decode
• Pull apart the instruction, set up the
operation in the ALU, and compute the
source and destination operand
addresses.
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Data Fetch
• Move the operands from memory to ALU
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Instruction Execute
• Compute the result of the operation in
the ALU
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Result Return
• Store the result from ALU into the
memory at the destination address.
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Pipelining
the CPU begins executing the second
instruction before the first one completes
•this results in faster processing
We omit the data
fetch step to decode
step to explain
pipelining idea.
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Microprocessor chips
• Word size
– Number of bits that can be accessed at one
time by the CPU
– The more bits in a word, the more powerful
the computer is
• Processing speed
–
–
–
–
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Millisecond: thousandth of a second
Microsecond: millionth of a second
Nanosecond: billionth of a second
Picosecond: trillionth of a second
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Microprocessor chips
• 2 types of microprocessor chips
– CISC chips
• Complex instruction set computer
• Thousands of programs written specially
for it
• Examples
– Intel: Pentium III, Pentium IV
– AMD: Athlon chip
–
RISC
chips
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Microprocessor chips
• 2 types of microprocessor chips
– CISC chips
– RISC chips
• Reduced instruction set computer
• Use fewer instructions, simpler and less
costly
• Examples
– Apple computers: PowerPC
– DEC: ALPHA
– Silicon Graph: MIPS
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Microprocessor chips
• Smart card: with specialized processor chips
–
–
–
–
Size of credit card
Has embedded chip
Store more information than magnetic strip card
Offer strong security and privacy
• Information contained in chip can be encrypted
• Protected by a password or pin number
– Examples
• Visa, MasterCard
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B. The Arithmetic and Logic Unit ( ALU )
Performs :
 arithmetic (+,-,*,/) operations
 logical (if hours > 40)
operations.
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C. Registers
 High speed temporary storage locations for data and
instructions
There are three main registers:
 Accumulator (Acc) :
•Used to store the results supplied by the ALU
 Program Counter (PC) :
•Remembers the location of the next program
instruction
 Instruction Register (IR)
•Holds the instruction to be executed
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Heat Sink
• heat sink
– a component designed to lower the
temperature of an electronic device
by dissipating heat into the
surrounding air
– All modern CPUs require a heat sink
• passive heat sink:a heat sink without a
fan
• active heat sink:a heat sink with a fan
– generally made of an aluminum alloy
and often have fans.
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Heat Pipe
• a heat transfer mechanism that can
transport large quantities of heat
with a very small difference in
temperature between the hot and
cold interfaces
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Parallel Processing
• the simultaneous use of more than one
CPU to execute a program
• Ideally, parallel processing makes a
program run faster because there are
more engines (CPUs) running it.
• In practice, it is often difficult to divide a
program in such a way that separate CPUs
can execute different portions without
interfering with each other.
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System Clock
• Located on a small specialized chip
• Produces precisely timed electrical beats
or impulse
• To coordinate and synchronize all
computer operations
• Clock speed is measured in gigahertz
– Gigahertz: billions of beats per second
– The faster the clock speed, the faster the
computer can process information
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Memory
• Holds data, instructions, information
• Contained on chips connected to the
system board
• 3 well-known types of memory chips
– RAM: random-access memory
– ROM: read-only memory
– CMOS: complementary metal-oxide
semiconductor
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Types of RAM
• dynamic RAM (DRAM)
– needs to be refreshed thousands
of times per second
– Slower but cheaper
• static RAM (SRAM)
– does not need to be refreshed
– faster but more expensive
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Memory
• RAM
– Hold the program and data that the CPU is
presently processing
• Data from secondary storage must be loaded into
RAM before it can be used
– A temporary or volatile storage
• When microcomputer is turned off, everything in
RAM is lost
• Save your work in time is very important
– Flash RAM/flash memory
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• Chips can retain data even if power is disrupted
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• A new type and more expensive
Memory
• RAM
– How to describe memory capacity?
•
•
•
•
Kilobyte(KB): 1024bytes
Megabyte(MB): 1024KB
Gigabyte(GB): 1024MB
Terabyte(TB): 1024GB
– Programs need enough memory to run
– Virtual memory
• Use hard disk to save part of a program which
should be in memory
• Most today’s OS support virtual memory
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Memory
• Cache memory/RAM cache
– A temporary high-speed holding area
between the memory and the CPU
– Store the most frequently accessed
information stored in RAM
– CPU can quickly access the information
from the cache
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Cache
 Helps to speed up the computer
 Stores frequently used instructions and data
 made of high-speed static RAM (SRAM)
When the processor needs an instruction or data,
it searches memory in this order:
（1） L1 Cache:built into the architecture of
microprocessors
（2） L2 Cache:sit between the CPU and the
DRAM
（3） L3 Cache
（4） RAM
（5）Hard disk/CD/DVD(called disk cache)
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disk cache
• a portion of RAM used to speed up access
to data on a disk
• can be part of the disk drive itself
–
–
–
–
a hard disk cache or buffer
more effective
more expensive
smaller
• can be general-purpose RAM in the
computer that is reserved for use by the
disk drive
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– a soft disk cache
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Memory
• ROM
– Read-only Memory, also called firmware
– Not volatile and cannot be changed by users
• nonvolatile
– Have programs built into them at the factory
• Typically contain special instructions
– Start the computer
– Give keyboard keys their special control capabilities
– Put characters on the screen
– CPU can read from it, but cannot write on it
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Memory
• CMOS
– complementary metal-oxide semiconductor
– Provides flexibility and expandability for a
computer system
• Flexible startup instructions
–
–
–
–
–
Amount of RAM
Type of keyboard
Mouse
Monitor
Disk drives
– Powered by a battery, does not lose its content when
computer power is off
– Contents can be changed when the system changes
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Firmware
• software (programs or data) that has
been written onto read-only memory
(ROM)
• is a combination of software and
hardware
• ROMs, PROMs and EPROMs that
have data or programs recorded on
them
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PROM
• Programmable Read-Only Memory
• is a memory chip on which you can store
a program.
• manufactured as blank chips on which
data can be written with a special device
called a PROM programmer.
• once the PROM has been used, you
cannot wipe it clean and use it to store
something else
• PROMs are nonvolatile
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EEPROM
• Electrically Erasable Programmable ReadOnly Memory, also called an E2PROM
• is a special type of PROM that can be
erased by exposing it to an electrical
charge
• retains its contents even when the power
is turned off
• Not as fast as RAM
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Expansion slots and cards
• Computer’s architecture
– Closed architecture
• users cannot easily add new devices in it
– Open architecture
• Most microcomputers have open architecture
• Users can expand their system
– Insert expansion cards into slots on the system board
» Expansion card: also called: plug-in
board/controller card/ adapter card/ interface card
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Expansion slots and cards
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Expansion slots and cards
• Kinds of expansion cards
– Network adapter cards
• Network Interface cards
• Connect a computer to other computers
• To form a network to share data, programs and hardware
– Modem cards/ internal modems
• Allow distant computers to communicate
• Digital signalanalog signal
– Digital signal: electronic signals in the system unit
– Analog signal: electronic signals over telephone lines
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Network adapter cards
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Expansion slots and cards
• Kinds of expansion cards
– TV tuner cards/television boards/personal
video recorder cards contain
• A TV tuner
• A video converter: changes TV signal into one
that can be displayed on the monitor
– PC cards/PCMCIA cards
• Used in portable computers
• Credit card-sized
• Have a variety of purpose
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TV Card
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PCMCIA and PC Card
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Expansion slots and cards
• Plug and play
– After insert a card and turn on the
computer
– The system start up and search the
device automatically and configure the
system
– Many Plug and play computer systems
exist today
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Bus lines
• Also called data bus
– Connects the parts of the CPU to each
other
– Links the CPU to various other
components on the system board
– Is a roadway along which bits travel
– The greater the capacity of a bus, the
more powerful and faster the operation
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Bus Lines
Address Bus
Data Bus
Control Bus
C
P
U
ROM
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RAM
Port
Port
Input
Device
Output
Device
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Bus lines
• 4 principal bus lines
– ISA: Industry standard architecture
• Developed for the IBM PC
• 8-bit-wide data path, 16 bits wide
• Still widely used
– PCI: Peripheral component interconnect
• High-speed 32-bit or 64-bit bus
• Over 20 times faster than ISA bus
• Expected to replace ISA bus in the near future
– AGP: Accelerated graphics port
• Over twice as fast as the PCI bus
• Widely used for graphics and 3-D animations
– USB: Universal serial bus
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• Combines with PCI bus on the system board
• Support several external devices
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ISA PCI and AGP
PCI
AGP
ISA
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Ports and cables
• Ports
– Connecting sockets on the outside of the system unit
– For specific devices: eg. Mouse, keyboard
– For a variety of different devices
• Serial ports
– Send data one bit a time
– Good for sending information over a long distance
• Parallel ports
– Send or receive a lot of data over a short distance
– Send 8 bits of data simultaneously across eight parallel wires
• USB ports
– Gradually replace serial and parallel ports
– Faster, can connect several devices on one USB port
• High performance serial bus(HPSB)/FireWire ports
– 33 times faster than USB ports
• Cables
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– Connect input and output devices to the system unit via the
ports
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mouse
Ports and Cables
keyboard
parallel
FireWire
network
Video
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serial
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Tutorial 1: CPU
1. A computer company claims to
have the fastest microcomputer at
6 GHz. What does this claim mean?
2. There
are
many
different
processors on the market today.
Common
examples
include
Pentium4, Celeron and Athlon.
Compare the 3 processors (speed,
cost, characteristics etc).
3. What is a heat sink and what is its
purpose?
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Tutorial 1: CPU
4. What is (a) ROM (b) RAM
(c) cache memory ?
5. Distinguish between static RAM and
dynamic RAM. What are the different
versions of each?
6. How much, many or long is a ...
bit, byte, kilobyte, megabyte, gigabyte,
terabyte, petabyte, word, millisecond,
microsecond, nanosecond, picosecond.
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Tutorial 1: CPU
7. The ASCII coding scheme uses the
decimal number 65 to represent the letter
'A', 90 as 'Z', 97 as 'a' and 122 as 'z'. What
is the word processor operator typing if
the following codes are received from the
keyboard by the microprocessor. (See
Appendix for the ASCII code)
• 84 114 121 32 105 116 33 10 13 78 111 116
104 105 110 103 32 105 115 32 105 109
112 111
•20:39 115 115 105 98 108 101 46 32 77 101 108 61
105 115 115 97 32 74 105 97 110 103 46
Tutorial 1: CPU
8. An expansion card is a circuit board that
fits into an expansion slot in the
motherboard. What is the purpose of the
following types of expansion cards: NIC,
modem card, graphics card, accelerator,
sound card, PC to TV, memory card.
9. What are the three main factors that
influence the speed of a processor?
10. Describe the differences between RISC
and CISC technologies including the
advantages and disadvantages.
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Tutorial 1: CPU
11.Give a description of
•
(a) flash memory
•
(b) pipelining.
12.Describe the following four different
types of ports: Serial, Parallel, USB
and SCSI. Give an example of a
device which can be connected to
each particular type of port.
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Machine Cycle
STEP 1: The control
unit fetches the maths
problem from memory
MEMORY
STEP 4: The results of
the maths problem are
stored in memory
STEP 2: The control
unit decodes the maths
problem and sends it to
the ALU
CPU
ALU
CONTROL
UNIT
STEP 3: The ALU
executes the maths
problem
IT Fundamentals
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