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
01:16 1
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
• 01:16
The basic components
–
System board, microprocessor, memory, system clock
–
Expansion slots and cards, bus lines, ports, cables
2
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
01:16 –
PDA system units
•
All inside
3
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
01:16 4
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
01:16 5
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
• 01:16
Unicode
– –
Designed to support international languages 16-bit code
–
Support from Apple, IBM and Microsoft
6
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
01:16 7
01:16
Example of coding
8
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
01:16 9
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
01:16 10
01:16 11
Microprocessor
• 01:16
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
12
01:16
2 Sides of a CPU
13
01:16
The principal subsystem of a computer
14
A. Control Unit
Control Unit Directs and co-ordinates most of the operations in the computer.
Interprets each instruction and then initiates the action.
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 15
Instruction Interpretation
• • •
Example:ADD 800, 428,884 PC(program counter): 2200 Computer before an ADD instruction
01:16 16
•
Instruction Fetch
Move instruction from memory to the control unit
01:16 17
01:16 •
Instruction Decode
Pull apart the instruction, set up the operation in the ALU, and compute the source and destination operand addresses.
18
•
Data Fetch
Move the operands from memory to ALU
01:16 19
Instruction Execute
•
Compute the result of the operation in the ALU
01:16 20
Result Return
•
Store the result from ALU into the memory at the destination address.
01:16 21
Pipelining
the CPU begins executing the second instruction before the first one completes
•
this results in faster processing
01:16
We omit the data fetch step to decode step to explain pipelining idea.
22
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
• 01:16
Processing speed
– – – –
Millisecond: thousandth of a second Microsecond: millionth of a second Nanosecond: billionth of a second Picosecond: trillionth of a second
23
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
01:16 –
RISC chips
24
Microprocessor chips
• 01:16
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
25
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
01:16 26
01:16 B. The Arithmetic and Logic Unit ( ALU )
Performs :
arithmetic (+,-,*,/) operations
logical (if hours > 40) operations.
27
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
01:16 28
01:16
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.
29
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
01:16 30
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.
01:16 31
System Clock
•
Located on a small specialized chip
•
Produces precisely timed electrical beats or impulse
•
To coordinate and synchronize all computer operations
• 01:16
Clock speed is measured in gigahertz
–
Gigahertz: billions of beats per second
–
The faster the clock speed, the faster the computer can process information
32
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
01:16 33
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
01:16 34
Memory
• 01:16
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
•
Chips can retain data even if power is disrupted
•
A new type and more expensive
35
Memory
• 01:16
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
36
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
01:16 37
Cache 01:16
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)
38
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
01:16 –
a soft disk cache
39
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
01:16 40
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
01:16 41
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
01:16 42
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
• 01:16
PROMs are nonvolatile
43
EEPROM
• • • •
Electrically Erasable Programmable Read Only Memory, also called an E 2 PROM 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
01:16 44
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
01:16 45
01:16
Expansion slots and cards
46
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
01:16 47
01:16
Network adapter cards
48
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
01:16 49
TV Card
01:16 50
01:16
PCMCIA and PC Card
51
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
01:16 52
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
01:16 53
C P U
01:16
Bus Lines
Address Bus Data Bus Control Bus
ROM RAM
Port Input Device Port Output Device
54
Bus lines
• 01:16
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
• •
Combines with PCI bus on the system board Support several external devices
55
PCI
ISA PCI and AGP
AGP ISA
01:16 56
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
01:16 –
Connect input and output devices to the system unit via the ports
57
mouse
Ports and Cables
keyboard parallel FireWire network
Video
01:16
serial
58
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 Pentium4, examples Celeron and include Athlon.
Compare the 3 processors (speed, cost, characteristics etc).
01:16
3. What is a heat sink and what is its purpose?
59
Tutorial 1: CPU
4. What is (a) (c) cache memory ?
ROM (b) RAM 5. Distinguish between static RAM and dynamic RAM. What are the different versions of each?
6. How much, many or long is a microsecond, nanosecond, picosecond.
...
bit, byte, kilobyte, megabyte, gigabyte, terabyte, petabyte, word, millisecond,
01:16 60
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
• 01:16
115 115 105 98 108 101 46 32 77 101 108 105 115 115 97 32 74 105 97 110 103 46
61
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
01:16
and CISC technologies including the advantages and disadvantages.
62
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.
01:16 63
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
ALU
CPU
CONTROL UNIT
STEP 2: The control unit decodes the maths problem and sends it to the ALU STEP 3: The ALU executes the maths problem
IT Fundamentals 64