2. Objectives Overview
Differentiate among various styles of system units on desktop computers, notebook computers, and mobile devices
Identify chips, adapter cards, and other components of a motherboard
Describe the control unit and arithmetic logic unit components of a processor, and explain the four steps in a machine cycle
Identify characteristics of various personal computer processors on the market today, and describe the ways processors are cooled
Define a bit and describe how a series of bits represents data
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3. Discovering Computers 2012: Chapter 4
The System Unit
The system unit is a case that contains electronic components of the computer used to process data.
Made of metal or plastic to protects the internal components from damage.
All computers have a system unit. It is available in variety of shapes & sizes.
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Figure 4-1

4. Discovering Computers 2012: Chapter 4

5. Discovering Computers 2012: Chapter 4
The System Unit
The inside of the system unit on a desktop personal computer includes:
Drive bay(s)
Power supply
Sound card
Video card
Processor
Memory
Processor interprets & carries out the basic instructions that operate a computer.
Memory holds data waiting to be processed & instruction waiting to be executed.
Processor & Memory are connected to a circuit board called the motherboard.
Adapter cards are circuit boards that provide connections and functions not built into the motherboard.
Devices outside the system unit often attach to the ports.
A drive bay holds one or more disk drive.
The Power supply provide the computer with the electricity.
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Figure 4-2

6. Discovering Computers 2012: Chapter 4
Motherboard
The motherboard is the main circuit board of the system unit.
Contains expansion slots, processor chips, and memory slots
Sometimes called a system board
Many electronic components attach to the motherboard, others are built into it. Ex: adapter cards, a processor chip and a memory module.
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Figure 4-3

7. Motherboard
Most computers use integrated circuits also called chips , for their CPU and main memory.
Memory chips are installed on memory module( card) that fit in a slot on the mother board.
What is a chip?
Small piece of semi-conducting material on which integrated circuits (IC) are etched.
IC contain many microscopic pathways capable of carrying electrical current.
Each IC can contain millions of elements such as resistors, capacitors, transistors.
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8. Discovering Computers 2012: Chapter 4
Processor
The processor, also called the central processing unit (CPU), interprets and carries out the basic instructions that operate a computer
Contain a control unit and an arithmetic logic unit (ALU) that work together to perform processing operations
Multi-core processor
Dual-core processor
Quad-core processor
A dual-core processor is a single chip that contains two separate processors
A multi-core processor is a chip with two or more separate processors
Each processor on a dual-core/multi-core chip generally runs at a slower clock speed, but increase overall performance
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9. Discovering Computers 2012: Chapter 4
Processor
The operations typically performed by a CPU are:
CPUs control the reading of programs and input files.
Its activates input unit to read program and data.
Controls the transmission of program & data files from disk to main memory.
CPUs process data according to instructions in a program.
Data can be processed arithmetically- number can be added, subtracted, multiplied and divided.
Logical tests can be performed on data. E.g., comparison.
Data can be transmitted or copied from one area of primary storage to another.
CPUs control the creation of output.
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Figure 4-4

10. Discovering Computers 2012: Chapter 4
Processor
The control unit is the component of the processor that directs and coordinates most of the operations in the computer.
Handles the transmission of data into and out of the CPU and supervises its overall operations.
Its interprets each instruction issued by a program & then initiates the appropriate action to carry out the instruction.
The arithmetic logic unit (ALU) performs arithmetic, comparison, and other operations.
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11. Discovering Computers 2012: Chapter 4
Processor
For every instruction, a processor repeats a set of four basic operations, which comprise a machine cycle
For every instruction, a processor repeats a set of four basic operations:
Fetching process of obtaining a program instruction or data item from memory.
Decoding process of translating the instruction into signals the computer can execute.
Executing process of carrying out the commands.
Storing, if necessary. Means writing the result to memory.
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Figure 4-5

12. Discovering Computers 2012: Chapter 4
Processor
The processor contains registers, that temporarily hold data and instructions
The system clock controls the timing of all computer operations
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13. Discovering Computers 2012: Chapter 4
Processor
Registers
The registers are special storage areas in the CPU.
Their function is to hold instructions, data values, memory addresses of both the instructions and data.
There are 4 basic types of it: CU, ALU
Instruction register hold instruction
Address register hold address of( data , next instruction ).
Storage register store data retrieved from main memory prior to processing.
Accumulator store the results of arithmetic & logic operations
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14. Discovering Computers 2012: Chapter 4
Processor
System clock
It generates regular electronic pulses , or ticks, that control the timing of all computer operations ( i.e. set operating pace of components of system unit)
Pace of system clock is clock speed. Most clock speeds are in the gigahertz (GHz) range (1 GHz = one billion ticks of system clock per second).
Processing actions occur at each “tick” of the electronic clock.
The Speed of the clock determines the speed at which the CPU can process data.
The faster the clock speed, the more instruction the processor can execute per second (hertz).
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15. Discovering Computers 2012: Chapter 4
Processor
Most current personal computers support pipelining
Processor begins fetching a second instruction before it completes the machine cycle for the first instruction
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16. Discovering Computers 2012: Chapter 4
Processor
Parallel processing uses multiple processors simultaneously to execute a single program or task
Massively parallel processing involves hundreds or thousands of processors
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17. Discovering Computers 2012: Chapter 4
Processor
The leading manufacturers of personal computer processor chips are Intel and AMD
They often identify their processor chip by a model name or model number.
Other leading processor chip manufacturers
Transmeta
IBM
Motorola
IBM processor had a different design from the Intel-style processor.
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Figure 4-7

18. Discovering Computers 2012: Chapter 4
Processor
Determine how you plan to use a new computer before selecting a processor
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Figure 4-8

19. Discovering Computers 2012: Chapter 4
Processor
A processor chip generates heat that could cause the chip to burn up
Require additional cooling
Heat sinks
Liquid cooling technology
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Figures 4-9 – 4-10

20. Discovering Computers 2012: Chapter 4
Data Representation
Analog signals are continuous and vary in strength and quality
Digital signals are in one of two states: on or off
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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21. Discovering Computers 2012: Chapter 4
Data Representation
A computer circuit represents the 0 or the 1 electronically by the presence or absence of an electrical charge
Eight bits grouped together as a unit are called a byte. A byte represents a single character in the computer ( numbers, upper or lower case letters, or punctuation marks)
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22. Discovering Computers 2012: Chapter 4
Data Representation
The different combinations of 0s and 1s are defined by patterns called a coding schema.
There are two coding schemas used to represent data
ASCII—American Standard Code for Information Interchange [Personal Computers – PCS]
EBCDIC—Extended Binary Coded Decimal Interchange Code [Mainframes, Mini-computers]
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Figure 4-14

23. Discovering Computers 2012: Chapter 4
Data Representation
ASCII is the most widely used coding scheme to represent data
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24. Discovering Computers 2012: Chapter 4
Data Representation
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Figure 4-15