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System Unit and its Components
Lecture # 3
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System Unit
It contains electronic components of the computers used to process data
system unit
system unit
system unit
system unit
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Components of SU
Processor Memory Adapter cards
Sound card Modem card
Ports Drive bays Power supply
power supply
ports
drive bays
processor
memory
sound card
video cardmodem cardnetwork card
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(Cont.)
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Motherboard
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
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Motherboard
processor chip adapter cards
memory chips
memory slots
motherboard
Expansionslots for adapter cards
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What is a chip?
Small piece of semi-conducting material on which integrated circuits are etched Integrated circuits contain
many microscopic pathways capable of carrying electrical current
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Central Processing Unit
Interprets and carries out basic instructions that operate a computer
Also called the processor
Processor
Control Unit
Arithmetic Logic Unit (ALU)
Arithmetic Logic Unit (ALU)
InputDevices
StorageDevices
OutputDevicesMemoryData Information
Information
DataInformatio
n
Information
DataInformatio
n
Control Unit
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Two Main components of CPU
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.
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Machine cycle
There are four operations of Machine CycleStep 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
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Pipelining
CPU begins fetching second instruction before completing machine cycle for first instruction
Results in faster processing
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System Clock
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)
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Factors affecting CPU performance
Registers Page # 145, topic: Registers Cache System Clock RAM
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Heat Sink and Heat Pipe
Heat sink—component with fins that cools processor
Heat pipe—smaller device for notebook computer
heat sink fan
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Parallel Processing
Using multiple processors simultaneously to execute a program faster
Requires special software to divide problem and bring results together
Control Processor
Processor 1
Memory
Processor 2
Memory
Processor 3
Memory
Processor 4
Memory
Results combined
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Data Representation
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)
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Byte
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
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Encoding Schemes
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 1111000000110001 1 1111000100110010 2 1111001000110011 3 11110011
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Data Representation How is a letter converted to binary form and back?
Step 1.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 3.The signal for the capital letter D is 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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Memory
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
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RAM (Random access Memory)
Home Task Explore SRAM, DRAM, SIMM, DIMM
and RIMMVirtual
Memory Small portion
of hard Disk acts as RAM
The more RAM a computer has, the faster it responds
Also called main memory
or primary storage
Most RAM is volatile, it is lost when computer’s
power is turned off
Memory chips that can be read from and written
to by processor
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Memory
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 bytesMegabyte MB 1 million bytesGigabyte GB 1 billion bytesTerabyte TB 1 trillion bytes
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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 hard disk. The operating system displays the user interface on the screen.
Operating system instructions
Operating system interface
RAM
Word processing program instructions
Word processing 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.
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Cache
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
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Registers
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
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ROM(Read Only Memory)
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)
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Flash 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
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CMOS
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
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Expansion Slots and Expansion Cards
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
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Expansion Slots and Expansion 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 cardsand other devices as you install them
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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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Serial Port
Transmits one bit of data at a time
Connects slow-speed devices, such as mouse, keyboard, modem
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Parallel Port
Connects devices that can transfer more than one bit at a time, such as a printer
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Bus
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)