1. Chapter 4 The Components of the System Unit
System unit: Case that contains electronic components
power supply
ports
drive bays
processor
memory
sound card
video card
modem card
network card
Chapter 4: System Unit

2. Motherboard Main circuit board in system unit
processor chip
adapter cards
memory chips
memory slots
motherboard
Expansion slots for adapter cards
Main circuit board in system unit
Contains adapter cards, processor chips, and memory chips
Chapter 4: System Unit
p. 128 Fig. 4-3
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3. Arithmetic Logic Unit (ALU)
Processor
Processor
Control Unit
Arithmetic Logic Unit (ALU)
CPU
Interprets and performs basic instructions
Control unit: coordinates operations
ALU: performs math functions
Control Unit
Arithmetic Logic Unit (ALU)
Instructions Data Information
Memory
Input Devices
Data
Information
Output Devices
Instructions Data Information
Storage Devices
Chapter 4: System Unit
p. 128 Fig. 4-4
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4. Pace of system clock is clock speed
Controls timing of all computer operations
Generates regular electronic pulses that set operating pace
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)
Chapter 4: System Unit
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5. Processor Faster processor, more expensive Click to view video
Chapter 4: System Unit
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6. Data Representation How do computers represent data?
Recognize only two discrete states: on or off
Use a binary system to recognize two states
Bytes: eight bits
Chapter 4: System Unit
p. 132 Fig. 4-6
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7. Data Representation What is a byte?
Eight bits grouped together as a unit
Provides enough different combinations of 0s and 1s to represent 256 individual characters
What is a byte?
Chapter 4: System Unit
p. 132 Fig. 4-7
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8. Data Representation
What are three popular coding systems to represent data?
ASCII— personal computers
EBCDIC—mainframes
ASCII Symbol EBCDIC
Chapter 4: System Unit
p. 132 Fig. 4-8
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9. Memory
Seat #2B4
Seat #2B3
What is memory?
Electronic components store instructions, data, and results
Consists of chips on motherboard
Each byte stored in unique location called an address
Chapter 4: System Unit
p. 134 Fig. 4-10
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10. Memory How is memory measured?
By number of bytes available for storage
Term Abbreviation Approximate Size
Kilobyte KB or K 1 thousand bytes
Megabyte MB 1 million bytes
Gigabyte GB 1 billion bytes
Terabyte TB 1 trillion bytes
Chapter 4: System Unit
p. 134 Fig. 4-11
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11. Memory What is random access memory (RAM)?
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
The more RAM a computer has, the faster it responds
Click to view Web Link, click Chapter 4, Click Web Link from left navigation, then click RAM below Chapter 4
Chapter 4: System Unit
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12. Memory How much RAM does an application require?
System Requirements
Windows® XP Home Edition/Professional
Intel Pentium processor at 233MHZ or higher
AMD K6 (Athlon Duron Family processor at 233MHZ or higher
64 MB of RAM
Software package indicates RAM requirements
For optimal performance, need more than minimum specifications
Chapter 4: System Unit
p. 136 Fig. 4-14
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13. Memory
What is cache?
Helps speed computer processes by storing frequently used instructions and data
L1 cache built into processor
L2 cache slower but has larger capacity
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14. Memory What is read-only memory (ROM)?
The data on most ROM chips cannot be modified
Memory chips that store permanent data and instructions
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15. Memory What is flash memory?’
Nonvolatile memory that can be erased electronically and reprogrammed
Click to view Web Link, click Chapter 4, Click Web Link from left navigation, then click Flash Memory below Chapter 4
Chapter 4: System Unit
p. 137 Fig. 4-15
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16. Stores date, time, and computer’s startup information
Memory
What is CMOS?
Uses battery power to retain information when other power is turned off
Stores date, time, and computer’s startup information
Chapter 4: System Unit
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17. Expansion Slots and Adapter Cards
What is an expansion slot?
An opening, or socket, on the motherboard that can hold an adapter card
Chapter 4: System Unit
p. 140 Fig. 4-19
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18. Ports and Connectors What is a serial port?
Transmits one bit of data at a time
Connects slow-speed devices, such as mouse, keyboard, modem
Chapter 4: System Unit
p. 142 Fig. 4-23
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19. Ports and Connectors What is a parallel port?
Connects devices that can transfer more than one bit at a time, such as a printer
Chapter 4: System Unit
p. 142 Fig. 4-24
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20. USB (universal serial bus) port
Ports and Connectors
USB (universal serial bus) port
What are USB ports?
PCs typically have four to eight USB ports on front or back of the system unit
Latest version is called USB 2.0
Can be used to attach multiple peripherals
Chapter 4: System Unit
p. 142
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21. Buses
What is a bus?
Channel allows devices to communicate with each other
Connects processor and RAM
Access times…
RAM, hard drive, floppy
Click to view Web Link, click Chapter 4, Click Web Link from left navigation, then click Buses below Chapter 4
Chapter 4: System Unit
p. 144 Fig. 4-25
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