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Chapter 2
The Components The Components of the System Unitof the System Unit
Prepared By: Humeyra Saracoglu
The System Unit
What is the system unit? Case that contains
system unit
electronic components of the computer used to process datato process data Sometimes called
the chassissystem unit
system unit
system unit
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The System Unit
What are common components inside the system unit? Processor power supply drive bays Memory Adapter cards Sound card
drive bays
processor
Sound card Modem card Video card
portsmemory
Network card Ports Drive bays sound card Drive bays Power supply
video card
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video cardmodem cardnetwork card
The System Unit
What is the motherboard? Main circuit
processor chipadapter cards
board in system unitC t i d t Contains adapter cards, processor chips, and
memory chips
c ps, dmemory chips
Also calledmemory slotssystem board memory slots
motherboard
Expansionslots for adapter cards
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The System Unitd l i li
What is a chip?dual inline packages (DIP) holds memory chips
Small piece of semi-conducting p gmaterial on which integrated circuits are etched
I t t d i it t i Integrated circuits contain many microscopic pathways capable of carrying electrical
pin grid array (PGA) package h ld
current Chips are packaged so they can
be attached to a circuit board holds processor chips
Click to view animation
be attached to a circuit board
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Click to view animation
Central Processing Unit
PP
What is the central processing unit (CPU)? Interprets and carries ProcessorProcessor
Control Control UnitUnit
Arithmetic Arithmetic Logic Unit (ALU)Logic Unit (ALU)
Arithmetic Arithmetic Logic Unit (ALU)Logic Unit (ALU)
Interprets and carries out basic instructions that operate a computer
Control Control UnitUnit
Control unit directs andInformationInformation
DataDataInformationInformation
Control unit directs and coordinates operations in computer Arithmetic logic unit
InputInputDevicesDevices
OutputOutputDevicesDevicesMemoryMemoryDataData InformationInformation
Arithmetic logic unit (ALU) performs arithmetic, comparison, and logical operations
InformationInformationDataData
InformationInformation
and logical operationsAlso called the processor
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StorageStorageDevicesDevices
Central Processing Unit
What is a machine cycle? Four operations of the CPU comprise a machine cycle
Step 1. FetchObtain program instructionor data item from memory
p p y
MemoryStep 2
Processor
Step 2.DecodeTranslate instruction into commands
Step 4. StoreWrite result to memory
Processor
Control UnitALUcommands
Step 3. ExecuteCarry out command
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The CPU Machine Cycle
Fetch The program’s binary code is “fetched” from its
temporary location in RAM and moved to the CPU.D dDecode The program’s binary code is decoded into commands
that the CPU understands.Execute The ALU performs the calculations. “Inside the Chip” by
IntelStore The results are stored in the registers.
Video Clip
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall
Making Computers Faster
Pipelining: The CPU processes more than one i i iinstruction at a time
Nonpipelined CPU
Fetch Decode Execute Store
Fetch Decode Execute Store
Instruction 1
Instruction 2
Nonpipelined CPU
Fetch Decode Execute Store Instruction 1
Pipelined CPU
Fetch Decode Execute Store
Fetch Decode Execute Store
Fetch Decode Execute Store
Instruction 2
Instruction 3
Instruction 4 Fetch Decode Execute Store Instruction 4
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall
Cache Memory
Small amount of memory ylocated on or near the CPU chip Stores recent or frequently used instructions and dataUsed for quick access byUsed for quick access by the CPUDifferent levels of cachee e eve s o c c e
Copyright © 2010 Pearson Education, Inc. Publishing as Prentice Hall
Central Processing Unit
What is a register? Temporary high-speed storage area that holds p y g p g
data and instructions
Stores location Stores location from where instruction from where instruction
was fetchedwas fetchedStores Stores
instruction while it is instruction while it is being decodedbeing decoded
Stores data Stores data while ALU while ALU computes itcomputes it
Stores results Stores results of calculationof calculation
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Central Processing Unit
How do personal computer processors compare?Comparison of Widely Usedp y
Personal Computer ProcessorsName Date Clock
Introduced Speed®Itanium 2 2002 1 GHZ and up
Xeon 2001 1.4–2.4 GHZ
Itanium 2001 733–800 MHZ
P i 4 2000 1 4 2 53 GH
®
™®®Pentium 4 2000 1.4–2.53 GHZ
Pentium III Xeon 1999 500–900 MHZ
Pentium III 1999 400 MHZ–1.2 GHZ
Celeron 1998 266 MHZ 1 8 GHZ
®
® ™
®®Celeron 1998 266 MHZ–1.8 GHZ
Operon 2003 To comeAthlon MP 2002 1.53–1.6 GHZ
Athlon XP 2001 1.33–1.73 GHZ
®™
™
™Click to view video
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Athlon 1999 500 MHZ–1.4 GHZ™
Data Representation
How do computers represent data? Most computers are digital
Recognize only two discrete states: on or off
p g
discrete states: on or off Use a binary system to
recognize two statesU N b i h Use Number system with two unique digits: 0 and 1, called bits (short for (binary digits)
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Data Representation
What is a byte? Eight bits grouped together as a unitg g p g Provides enough different combinations of 0s and 1s
to represent 256 individual charactersb Numbers
Uppercase and lowercaseand lowercase letters
Punctuation marks
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Data Representation
How is a letter converted to binary form and back?Step 1.
St 2p
The user presses the capital letter D(shift+D key) on the keyboard.
Step 2.An electronic signal for the capital letter D is sent to the system unit.
Step 3S Step 3.The signal for the capital letter Dis converted to its ASCII binary code (01000100) and is stored in memory for processing.
Step 4.After processing, the binary code for the capital letter D is converted to an image, and displayed on the output device
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y p gdisplayed on the output device.
Memory
What is memory? Electronic components that
Seat #2B4 Seat #2B3
store instructions, data, and results
Consists of one or Consists of one or more chips on motherboard orth i it b dother circuit board
Each byte stored in unique location called an address, similar to addresses on a passenger train
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on a passenger train
Memory
How is memory measured? By number of bytes available for storage
Term Abbreviation Approximate Size
y y g
Kilobyte KB or K 1 thousand bytesMegabyte MB 1 million bytesGigabyte GB 1 billion bytesTerabyte TB 1 trillion bytesTerabyte TB 1 trillion bytes
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Memory
What is random access memory (RAM)?
Memory chips that can be Memory chips that can be read from and written read from and written
to by processorto by processor
Also called Also called main memorymain memory
oror primaryprimary
Most RAM is Most RAM is volatilevolatile, it is lost , it is lost when computer’s when computer’s
y py p
The more RAM aThe more RAM a
or or primary primary storagestorage power is power is
turned offturned off
The more RAM a The more RAM a computer has, the computer has, the faster it respondsfaster it responds
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Memory
How do program instructions transfer in and out of RAM?Step 1. When you start the computer, certain operating system files load into RAM from the
RAM
operating system files load into RAM from the hard disk. The operating system displays the user interface on the screen.
Operating system Operating system instructionsinstructions
Operating system Operating system interfaceinterface
Step 2. When you start a Web browser, the program’s instructions load into RAM from the
Web browser Web browser instructionsinstructions
Web browser Web browser windowwindow
hard disk. The Web browser window is displayed on the screen.
Step 3. When you start a word processing program, the program’s instructions load into RAM f th h d di k Th d i
Word processing Word processing program instructionsprogram instructions
Word processing Word processing program windowprogram window
RAM
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.
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.
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Web browser program Web browser program instructions are instructions are
removed from RAMremoved from RAM
Web browser Web browser window no longer is window no longer is
displayed on displayed on desktopdesktop
Memory
How much RAM do you need? Depends on type of applications you intend to runp yp pp y
on your computerRAM 128 to 256 MB 256 to 1 GB 1 GB and up
Use • Home and businessusers managingpersonal finance
• Using standard
• Users requiring more advanced multimedia capabilities
• Running number-intensiveaccounting, financial, or
• Power users creating professional Web sites
• Running sophisticatedCAD, 3D design, or
application softwaresuch as word processing
• Using educational or entertainment
spreadsheet programs• Using voice recognition• Working with videos, music, and
digital imaging
other graphics-intensive software
or entertainmentCD-ROMs
• Communicating with others on the Web
digital imaging• Creating Web sites• Participating in video conferences• Playing Internet games
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Memory
What is read-only memory (ROM)?M hi th t tM hi th t t ii i ii iMemory chips that store Memory chips that store
permanent data permanent data and instructionsand instructions
Nonvolatile memoryNonvolatile memory, it is not , it is not lost when computer’s lost when computer’s
power is turned offpower is turned off
Three types:Three types:
FirmwareFirmware——
EEPROMEEPROM((eelectrically lectrically
eerasable rasable pprogrammable rogrammable rreadead--oonly nly mmemory)emory)——
Type of PROMType of PROMManufactured with Manufactured with permanently written permanently written data, instructions, data, instructions, or informationor information
Type of PROM Type of PROM containing microcode containing microcode
programmer programmer can erasecan erase
PROMPROM((pprogrammable rogrammable
rreadead--oonly nly mmemory)emory)——y)y)
Blank ROM Blank ROM chip onto which chip onto which a programmer a programmer
can write permanentlycan write permanently
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Ports
What are ports and connectors? Port connects external devices to system unit Connector joins cable to peripheral
Available in one of two genders: male and female
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